1.. SPDX-License-Identifier: GPL-2.0+ 2.. sectionauthor:: Simon Glass <sjg@chromium.org> 3 4Design Details 5============== 6 7This README contains high-level information about driver model, a unified 8way of declaring and accessing drivers in U-Boot. The original work was done 9by: 10 11 * Marek Vasut <marex@denx.de> 12 * Pavel Herrmann <morpheus.ibis@gmail.com> 13 * Viktor Křivák <viktor.krivak@gmail.com> 14 * Tomas Hlavacek <tmshlvck@gmail.com> 15 16This has been both simplified and extended into the current implementation 17by: 18 19 * Simon Glass <sjg@chromium.org> 20 21 22Terminology 23----------- 24 25Uclass 26 a group of devices which operate in the same way. A uclass provides 27 a way of accessing individual devices within the group, but always 28 using the same interface. For example a GPIO uclass provides 29 operations for get/set value. An I2C uclass may have 10 I2C ports, 30 4 with one driver, and 6 with another. 31 32Driver 33 some code which talks to a peripheral and presents a higher-level 34 interface to it. 35 36Device 37 an instance of a driver, tied to a particular port or peripheral. 38 39 40How to try it 41------------- 42 43Build U-Boot sandbox and run it:: 44 45 make sandbox_defconfig 46 make 47 ./u-boot -d u-boot.dtb 48 49 (type 'reset' to exit U-Boot) 50 51 52There is a uclass called 'demo'. This uclass handles 53saying hello, and reporting its status. There are two drivers in this 54uclass: 55 56 - simple: Just prints a message for hello, doesn't implement status 57 - shape: Prints shapes and reports number of characters printed as status 58 59The demo class is pretty simple, but not trivial. The intention is that it 60can be used for testing, so it will implement all driver model features and 61provide good code coverage of them. It does have multiple drivers, it 62handles parameter data and platdata (data which tells the driver how 63to operate on a particular platform) and it uses private driver data. 64 65To try it, see the example session below:: 66 67 =>demo hello 1 68 Hello '@' from 07981110: red 4 69 =>demo status 2 70 Status: 0 71 =>demo hello 2 72 g 73 r@ 74 e@@ 75 e@@@ 76 n@@@@ 77 g@@@@@ 78 =>demo status 2 79 Status: 21 80 =>demo hello 4 ^ 81 y^^^ 82 e^^^^^ 83 l^^^^^^^ 84 l^^^^^^^ 85 o^^^^^ 86 w^^^ 87 =>demo status 4 88 Status: 36 89 => 90 91 92Running the tests 93----------------- 94 95The intent with driver model is that the core portion has 100% test coverage 96in sandbox, and every uclass has its own test. As a move towards this, tests 97are provided in test/dm. To run them, try:: 98 99 ./test/py/test.py --bd sandbox --build -k ut_dm -v 100 101You should see something like this:: 102 103 (venv)$ ./test/py/test.py --bd sandbox --build -k ut_dm -v 104 +make O=/root/u-boot/build-sandbox -s sandbox_defconfig 105 +make O=/root/u-boot/build-sandbox -s -j8 106 ============================= test session starts ============================== 107 platform linux2 -- Python 2.7.5, pytest-2.9.0, py-1.4.31, pluggy-0.3.1 -- /root/u-boot/venv/bin/python 108 cachedir: .cache 109 rootdir: /root/u-boot, inifile: 110 collected 199 items 111 112 test/py/tests/test_ut.py::test_ut_dm_init PASSED 113 test/py/tests/test_ut.py::test_ut[ut_dm_adc_bind] PASSED 114 test/py/tests/test_ut.py::test_ut[ut_dm_adc_multi_channel_conversion] PASSED 115 test/py/tests/test_ut.py::test_ut[ut_dm_adc_multi_channel_shot] PASSED 116 test/py/tests/test_ut.py::test_ut[ut_dm_adc_single_channel_conversion] PASSED 117 test/py/tests/test_ut.py::test_ut[ut_dm_adc_single_channel_shot] PASSED 118 test/py/tests/test_ut.py::test_ut[ut_dm_adc_supply] PASSED 119 test/py/tests/test_ut.py::test_ut[ut_dm_adc_wrong_channel_selection] PASSED 120 test/py/tests/test_ut.py::test_ut[ut_dm_autobind] PASSED 121 test/py/tests/test_ut.py::test_ut[ut_dm_autobind_uclass_pdata_alloc] PASSED 122 test/py/tests/test_ut.py::test_ut[ut_dm_autobind_uclass_pdata_valid] PASSED 123 test/py/tests/test_ut.py::test_ut[ut_dm_autoprobe] PASSED 124 test/py/tests/test_ut.py::test_ut[ut_dm_bus_child_post_bind] PASSED 125 test/py/tests/test_ut.py::test_ut[ut_dm_bus_child_post_bind_uclass] PASSED 126 test/py/tests/test_ut.py::test_ut[ut_dm_bus_child_pre_probe_uclass] PASSED 127 test/py/tests/test_ut.py::test_ut[ut_dm_bus_children] PASSED 128 test/py/tests/test_ut.py::test_ut[ut_dm_bus_children_funcs] PASSED 129 test/py/tests/test_ut.py::test_ut[ut_dm_bus_children_iterators] PASSED 130 test/py/tests/test_ut.py::test_ut[ut_dm_bus_parent_data] PASSED 131 test/py/tests/test_ut.py::test_ut[ut_dm_bus_parent_data_uclass] PASSED 132 test/py/tests/test_ut.py::test_ut[ut_dm_bus_parent_ops] PASSED 133 test/py/tests/test_ut.py::test_ut[ut_dm_bus_parent_platdata] PASSED 134 test/py/tests/test_ut.py::test_ut[ut_dm_bus_parent_platdata_uclass] PASSED 135 test/py/tests/test_ut.py::test_ut[ut_dm_children] PASSED 136 test/py/tests/test_ut.py::test_ut[ut_dm_clk_base] PASSED 137 test/py/tests/test_ut.py::test_ut[ut_dm_clk_periph] PASSED 138 test/py/tests/test_ut.py::test_ut[ut_dm_device_get_uclass_id] PASSED 139 test/py/tests/test_ut.py::test_ut[ut_dm_eth] PASSED 140 test/py/tests/test_ut.py::test_ut[ut_dm_eth_act] PASSED 141 test/py/tests/test_ut.py::test_ut[ut_dm_eth_alias] PASSED 142 test/py/tests/test_ut.py::test_ut[ut_dm_eth_prime] PASSED 143 test/py/tests/test_ut.py::test_ut[ut_dm_eth_rotate] PASSED 144 test/py/tests/test_ut.py::test_ut[ut_dm_fdt] PASSED 145 test/py/tests/test_ut.py::test_ut[ut_dm_fdt_offset] PASSED 146 test/py/tests/test_ut.py::test_ut[ut_dm_fdt_pre_reloc] PASSED 147 test/py/tests/test_ut.py::test_ut[ut_dm_fdt_uclass_seq] PASSED 148 test/py/tests/test_ut.py::test_ut[ut_dm_gpio] PASSED 149 test/py/tests/test_ut.py::test_ut[ut_dm_gpio_anon] PASSED 150 test/py/tests/test_ut.py::test_ut[ut_dm_gpio_copy] PASSED 151 test/py/tests/test_ut.py::test_ut[ut_dm_gpio_leak] PASSED 152 test/py/tests/test_ut.py::test_ut[ut_dm_gpio_phandles] PASSED 153 test/py/tests/test_ut.py::test_ut[ut_dm_gpio_requestf] PASSED 154 test/py/tests/test_ut.py::test_ut[ut_dm_i2c_bytewise] PASSED 155 test/py/tests/test_ut.py::test_ut[ut_dm_i2c_find] PASSED 156 test/py/tests/test_ut.py::test_ut[ut_dm_i2c_offset] PASSED 157 test/py/tests/test_ut.py::test_ut[ut_dm_i2c_offset_len] PASSED 158 test/py/tests/test_ut.py::test_ut[ut_dm_i2c_probe_empty] PASSED 159 test/py/tests/test_ut.py::test_ut[ut_dm_i2c_read_write] PASSED 160 test/py/tests/test_ut.py::test_ut[ut_dm_i2c_speed] PASSED 161 test/py/tests/test_ut.py::test_ut[ut_dm_leak] PASSED 162 test/py/tests/test_ut.py::test_ut[ut_dm_led_base] PASSED 163 test/py/tests/test_ut.py::test_ut[ut_dm_led_gpio] PASSED 164 test/py/tests/test_ut.py::test_ut[ut_dm_led_label] PASSED 165 test/py/tests/test_ut.py::test_ut[ut_dm_lifecycle] PASSED 166 test/py/tests/test_ut.py::test_ut[ut_dm_mmc_base] PASSED 167 test/py/tests/test_ut.py::test_ut[ut_dm_net_retry] PASSED 168 test/py/tests/test_ut.py::test_ut[ut_dm_operations] PASSED 169 test/py/tests/test_ut.py::test_ut[ut_dm_ordering] PASSED 170 test/py/tests/test_ut.py::test_ut[ut_dm_pci_base] PASSED 171 test/py/tests/test_ut.py::test_ut[ut_dm_pci_busnum] PASSED 172 test/py/tests/test_ut.py::test_ut[ut_dm_pci_swapcase] PASSED 173 test/py/tests/test_ut.py::test_ut[ut_dm_platdata] PASSED 174 test/py/tests/test_ut.py::test_ut[ut_dm_power_pmic_get] PASSED 175 test/py/tests/test_ut.py::test_ut[ut_dm_power_pmic_io] PASSED 176 test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_autoset] PASSED 177 test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_autoset_list] PASSED 178 test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_get] PASSED 179 test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_set_get_current] PASSED 180 test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_set_get_enable] PASSED 181 test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_set_get_mode] PASSED 182 test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_set_get_voltage] PASSED 183 test/py/tests/test_ut.py::test_ut[ut_dm_pre_reloc] PASSED 184 test/py/tests/test_ut.py::test_ut[ut_dm_ram_base] PASSED 185 test/py/tests/test_ut.py::test_ut[ut_dm_regmap_base] PASSED 186 test/py/tests/test_ut.py::test_ut[ut_dm_regmap_syscon] PASSED 187 test/py/tests/test_ut.py::test_ut[ut_dm_remoteproc_base] PASSED 188 test/py/tests/test_ut.py::test_ut[ut_dm_remove] PASSED 189 test/py/tests/test_ut.py::test_ut[ut_dm_reset_base] PASSED 190 test/py/tests/test_ut.py::test_ut[ut_dm_reset_walk] PASSED 191 test/py/tests/test_ut.py::test_ut[ut_dm_rtc_base] PASSED 192 test/py/tests/test_ut.py::test_ut[ut_dm_rtc_dual] PASSED 193 test/py/tests/test_ut.py::test_ut[ut_dm_rtc_reset] PASSED 194 test/py/tests/test_ut.py::test_ut[ut_dm_rtc_set_get] PASSED 195 test/py/tests/test_ut.py::test_ut[ut_dm_spi_find] PASSED 196 test/py/tests/test_ut.py::test_ut[ut_dm_spi_flash] PASSED 197 test/py/tests/test_ut.py::test_ut[ut_dm_spi_xfer] PASSED 198 test/py/tests/test_ut.py::test_ut[ut_dm_syscon_base] PASSED 199 test/py/tests/test_ut.py::test_ut[ut_dm_syscon_by_driver_data] PASSED 200 test/py/tests/test_ut.py::test_ut[ut_dm_timer_base] PASSED 201 test/py/tests/test_ut.py::test_ut[ut_dm_uclass] PASSED 202 test/py/tests/test_ut.py::test_ut[ut_dm_uclass_before_ready] PASSED 203 test/py/tests/test_ut.py::test_ut[ut_dm_uclass_devices_find] PASSED 204 test/py/tests/test_ut.py::test_ut[ut_dm_uclass_devices_find_by_name] PASSED 205 test/py/tests/test_ut.py::test_ut[ut_dm_uclass_devices_get] PASSED 206 test/py/tests/test_ut.py::test_ut[ut_dm_uclass_devices_get_by_name] PASSED 207 test/py/tests/test_ut.py::test_ut[ut_dm_usb_base] PASSED 208 test/py/tests/test_ut.py::test_ut[ut_dm_usb_flash] PASSED 209 test/py/tests/test_ut.py::test_ut[ut_dm_usb_keyb] PASSED 210 test/py/tests/test_ut.py::test_ut[ut_dm_usb_multi] PASSED 211 test/py/tests/test_ut.py::test_ut[ut_dm_usb_remove] PASSED 212 test/py/tests/test_ut.py::test_ut[ut_dm_usb_tree] PASSED 213 test/py/tests/test_ut.py::test_ut[ut_dm_usb_tree_remove] PASSED 214 test/py/tests/test_ut.py::test_ut[ut_dm_usb_tree_reorder] PASSED 215 test/py/tests/test_ut.py::test_ut[ut_dm_video_base] PASSED 216 test/py/tests/test_ut.py::test_ut[ut_dm_video_bmp] PASSED 217 test/py/tests/test_ut.py::test_ut[ut_dm_video_bmp_comp] PASSED 218 test/py/tests/test_ut.py::test_ut[ut_dm_video_chars] PASSED 219 test/py/tests/test_ut.py::test_ut[ut_dm_video_context] PASSED 220 test/py/tests/test_ut.py::test_ut[ut_dm_video_rotation1] PASSED 221 test/py/tests/test_ut.py::test_ut[ut_dm_video_rotation2] PASSED 222 test/py/tests/test_ut.py::test_ut[ut_dm_video_rotation3] PASSED 223 test/py/tests/test_ut.py::test_ut[ut_dm_video_text] PASSED 224 test/py/tests/test_ut.py::test_ut[ut_dm_video_truetype] PASSED 225 test/py/tests/test_ut.py::test_ut[ut_dm_video_truetype_bs] PASSED 226 test/py/tests/test_ut.py::test_ut[ut_dm_video_truetype_scroll] PASSED 227 228 ======================= 84 tests deselected by '-kut_dm' ======================= 229 ================== 115 passed, 84 deselected in 3.77 seconds =================== 230 231What is going on? 232----------------- 233 234Let's start at the top. The demo command is in common/cmd_demo.c. It does 235the usual command processing and then: 236 237.. code-block:: c 238 239 struct udevice *demo_dev; 240 241 ret = uclass_get_device(UCLASS_DEMO, devnum, &demo_dev); 242 243UCLASS_DEMO means the class of devices which implement 'demo'. Other 244classes might be MMC, or GPIO, hashing or serial. The idea is that the 245devices in the class all share a particular way of working. The class 246presents a unified view of all these devices to U-Boot. 247 248This function looks up a device for the demo uclass. Given a device 249number we can find the device because all devices have registered with 250the UCLASS_DEMO uclass. 251 252The device is automatically activated ready for use by uclass_get_device(). 253 254Now that we have the device we can do things like: 255 256.. code-block:: c 257 258 return demo_hello(demo_dev, ch); 259 260This function is in the demo uclass. It takes care of calling the 'hello' 261method of the relevant driver. Bearing in mind that there are two drivers, 262this particular device may use one or other of them. 263 264The code for demo_hello() is in drivers/demo/demo-uclass.c: 265 266.. code-block:: c 267 268 int demo_hello(struct udevice *dev, int ch) 269 { 270 const struct demo_ops *ops = device_get_ops(dev); 271 272 if (!ops->hello) 273 return -ENOSYS; 274 275 return ops->hello(dev, ch); 276 } 277 278As you can see it just calls the relevant driver method. One of these is 279in drivers/demo/demo-simple.c: 280 281.. code-block:: c 282 283 static int simple_hello(struct udevice *dev, int ch) 284 { 285 const struct dm_demo_pdata *pdata = dev_get_platdata(dev); 286 287 printf("Hello from %08x: %s %d\n", map_to_sysmem(dev), 288 pdata->colour, pdata->sides); 289 290 return 0; 291 } 292 293 294So that is a trip from top (command execution) to bottom (driver action) 295but it leaves a lot of topics to address. 296 297 298Declaring Drivers 299----------------- 300 301A driver declaration looks something like this (see 302drivers/demo/demo-shape.c): 303 304.. code-block:: c 305 306 static const struct demo_ops shape_ops = { 307 .hello = shape_hello, 308 .status = shape_status, 309 }; 310 311 U_BOOT_DRIVER(demo_shape_drv) = { 312 .name = "demo_shape_drv", 313 .id = UCLASS_DEMO, 314 .ops = &shape_ops, 315 .priv_data_size = sizeof(struct shape_data), 316 }; 317 318 319This driver has two methods (hello and status) and requires a bit of 320private data (accessible through dev_get_priv(dev) once the driver has 321been probed). It is a member of UCLASS_DEMO so will register itself 322there. 323 324In U_BOOT_DRIVER it is also possible to specify special methods for bind 325and unbind, and these are called at appropriate times. For many drivers 326it is hoped that only 'probe' and 'remove' will be needed. 327 328The U_BOOT_DRIVER macro creates a data structure accessible from C, 329so driver model can find the drivers that are available. 330 331The methods a device can provide are documented in the device.h header. 332Briefly, they are: 333 334 * bind - make the driver model aware of a device (bind it to its driver) 335 * unbind - make the driver model forget the device 336 * ofdata_to_platdata - convert device tree data to platdata - see later 337 * probe - make a device ready for use 338 * remove - remove a device so it cannot be used until probed again 339 340The sequence to get a device to work is bind, ofdata_to_platdata (if using 341device tree) and probe. 342 343 344Platform Data 345------------- 346 347Note: platform data is the old way of doing things. It is 348basically a C structure which is passed to drivers to tell them about 349platform-specific settings like the address of its registers, bus 350speed, etc. Device tree is now the preferred way of handling this. 351Unless you have a good reason not to use device tree (the main one 352being you need serial support in SPL and don't have enough SRAM for 353the cut-down device tree and libfdt libraries) you should stay away 354from platform data. 355 356Platform data is like Linux platform data, if you are familiar with that. 357It provides the board-specific information to start up a device. 358 359Why is this information not just stored in the device driver itself? The 360idea is that the device driver is generic, and can in principle operate on 361any board that has that type of device. For example, with modern 362highly-complex SoCs it is common for the IP to come from an IP vendor, and 363therefore (for example) the MMC controller may be the same on chips from 364different vendors. It makes no sense to write independent drivers for the 365MMC controller on each vendor's SoC, when they are all almost the same. 366Similarly, we may have 6 UARTs in an SoC, all of which are mostly the same, 367but lie at different addresses in the address space. 368 369Using the UART example, we have a single driver and it is instantiated 6 370times by supplying 6 lots of platform data. Each lot of platform data 371gives the driver name and a pointer to a structure containing information 372about this instance - e.g. the address of the register space. It may be that 373one of the UARTS supports RS-485 operation - this can be added as a flag in 374the platform data, which is set for this one port and clear for the rest. 375 376Think of your driver as a generic piece of code which knows how to talk to 377a device, but needs to know where it is, any variant/option information and 378so on. Platform data provides this link between the generic piece of code 379and the specific way it is bound on a particular board. 380 381Examples of platform data include: 382 383 - The base address of the IP block's register space 384 - Configuration options, like: 385 - the SPI polarity and maximum speed for a SPI controller 386 - the I2C speed to use for an I2C device 387 - the number of GPIOs available in a GPIO device 388 389Where does the platform data come from? It is either held in a structure 390which is compiled into U-Boot, or it can be parsed from the Device Tree 391(see 'Device Tree' below). 392 393For an example of how it can be compiled in, see demo-pdata.c which 394sets up a table of driver names and their associated platform data. 395The data can be interpreted by the drivers however they like - it is 396basically a communication scheme between the board-specific code and 397the generic drivers, which are intended to work on any board. 398 399Drivers can access their data via dev->info->platdata. Here is 400the declaration for the platform data, which would normally appear 401in the board file. 402 403.. code-block:: c 404 405 static const struct dm_demo_cdata red_square = { 406 .colour = "red", 407 .sides = 4. 408 }; 409 410 static const struct driver_info info[] = { 411 { 412 .name = "demo_shape_drv", 413 .platdata = &red_square, 414 }, 415 }; 416 417 demo1 = driver_bind(root, &info[0]); 418 419 420Device Tree 421----------- 422 423While platdata is useful, a more flexible way of providing device data is 424by using device tree. In U-Boot you should use this where possible. Avoid 425sending patches which make use of the U_BOOT_DEVICE() macro unless strictly 426necessary. 427 428With device tree we replace the above code with the following device tree 429fragment: 430 431.. code-block:: c 432 433 red-square { 434 compatible = "demo-shape"; 435 colour = "red"; 436 sides = <4>; 437 }; 438 439This means that instead of having lots of U_BOOT_DEVICE() declarations in 440the board file, we put these in the device tree. This approach allows a lot 441more generality, since the same board file can support many types of boards 442(e,g. with the same SoC) just by using different device trees. An added 443benefit is that the Linux device tree can be used, thus further simplifying 444the task of board-bring up either for U-Boot or Linux devs (whoever gets to 445the board first!). 446 447The easiest way to make this work it to add a few members to the driver: 448 449.. code-block:: c 450 451 .platdata_auto_alloc_size = sizeof(struct dm_test_pdata), 452 .ofdata_to_platdata = testfdt_ofdata_to_platdata, 453 454The 'auto_alloc' feature allowed space for the platdata to be allocated 455and zeroed before the driver's ofdata_to_platdata() method is called. The 456ofdata_to_platdata() method, which the driver write supplies, should parse 457the device tree node for this device and place it in dev->platdata. Thus 458when the probe method is called later (to set up the device ready for use) 459the platform data will be present. 460 461Note that both methods are optional. If you provide an ofdata_to_platdata 462method then it will be called first (during activation). If you provide a 463probe method it will be called next. See Driver Lifecycle below for more 464details. 465 466If you don't want to have the platdata automatically allocated then you 467can leave out platdata_auto_alloc_size. In this case you can use malloc 468in your ofdata_to_platdata (or probe) method to allocate the required memory, 469and you should free it in the remove method. 470 471The driver model tree is intended to mirror that of the device tree. The 472root driver is at device tree offset 0 (the root node, '/'), and its 473children are the children of the root node. 474 475In order for a device tree to be valid, the content must be correct with 476respect to either device tree specification 477(https://www.devicetree.org/specifications/) or the device tree bindings that 478are found in the doc/device-tree-bindings directory. When not U-Boot specific 479the bindings in this directory tend to come from the Linux Kernel. As such 480certain design decisions may have been made already for us in terms of how 481specific devices are described and bound. In most circumstances we wish to 482retain compatibility without additional changes being made to the device tree 483source files. 484 485Declaring Uclasses 486------------------ 487 488The demo uclass is declared like this: 489 490.. code-block:: c 491 492 U_BOOT_CLASS(demo) = { 493 .id = UCLASS_DEMO, 494 }; 495 496It is also possible to specify special methods for probe, etc. The uclass 497numbering comes from include/dm/uclass.h. To add a new uclass, add to the 498end of the enum there, then declare your uclass as above. 499 500 501Device Sequence Numbers 502----------------------- 503 504U-Boot numbers devices from 0 in many situations, such as in the command 505line for I2C and SPI buses, and the device names for serial ports (serial0, 506serial1, ...). Driver model supports this numbering and permits devices 507to be locating by their 'sequence'. This numbering uniquely identifies a 508device in its uclass, so no two devices within a particular uclass can have 509the same sequence number. 510 511Sequence numbers start from 0 but gaps are permitted. For example, a board 512may have I2C buses 1, 4, 5 but no 0, 2 or 3. The choice of how devices are 513numbered is up to a particular board, and may be set by the SoC in some 514cases. While it might be tempting to automatically renumber the devices 515where there are gaps in the sequence, this can lead to confusion and is 516not the way that U-Boot works. 517 518Each device can request a sequence number. If none is required then the 519device will be automatically allocated the next available sequence number. 520 521To specify the sequence number in the device tree an alias is typically 522used. Make sure that the uclass has the DM_UC_FLAG_SEQ_ALIAS flag set. 523 524.. code-block:: none 525 526 aliases { 527 serial2 = "/serial@22230000"; 528 }; 529 530This indicates that in the uclass called "serial", the named node 531("/serial@22230000") will be given sequence number 2. Any command or driver 532which requests serial device 2 will obtain this device. 533 534More commonly you can use node references, which expand to the full path: 535 536.. code-block:: none 537 538 aliases { 539 serial2 = &serial_2; 540 }; 541 ... 542 serial_2: serial@22230000 { 543 ... 544 }; 545 546The alias resolves to the same string in this case, but this version is 547easier to read. 548 549Device sequence numbers are resolved when a device is probed. Before then 550the sequence number is only a request which may or may not be honoured, 551depending on what other devices have been probed. However the numbering is 552entirely under the control of the board author so a conflict is generally 553an error. 554 555 556Bus Drivers 557----------- 558 559A common use of driver model is to implement a bus, a device which provides 560access to other devices. Example of buses include SPI and I2C. Typically 561the bus provides some sort of transport or translation that makes it 562possible to talk to the devices on the bus. 563 564Driver model provides some useful features to help with implementing buses. 565Firstly, a bus can request that its children store some 'parent data' which 566can be used to keep track of child state. Secondly, the bus can define 567methods which are called when a child is probed or removed. This is similar 568to the methods the uclass driver provides. Thirdly, per-child platform data 569can be provided to specify things like the child's address on the bus. This 570persists across child probe()/remove() cycles. 571 572For consistency and ease of implementation, the bus uclass can specify the 573per-child platform data, so that it can be the same for all children of buses 574in that uclass. There are also uclass methods which can be called when 575children are bound and probed. 576 577Here an explanation of how a bus fits with a uclass may be useful. Consider 578a USB bus with several devices attached to it, each from a different (made 579up) uclass:: 580 581 xhci_usb (UCLASS_USB) 582 eth (UCLASS_ETHERNET) 583 camera (UCLASS_CAMERA) 584 flash (UCLASS_FLASH_STORAGE) 585 586Each of the devices is connected to a different address on the USB bus. 587The bus device wants to store this address and some other information such 588as the bus speed for each device. 589 590To achieve this, the bus device can use dev->parent_platdata in each of its 591three children. This can be auto-allocated if the bus driver (or bus uclass) 592has a non-zero value for per_child_platdata_auto_alloc_size. If not, then 593the bus device or uclass can allocate the space itself before the child 594device is probed. 595 596Also the bus driver can define the child_pre_probe() and child_post_remove() 597methods to allow it to do some processing before the child is activated or 598after it is deactivated. 599 600Similarly the bus uclass can define the child_post_bind() method to obtain 601the per-child platform data from the device tree and set it up for the child. 602The bus uclass can also provide a child_pre_probe() method. Very often it is 603the bus uclass that controls these features, since it avoids each driver 604having to do the same processing. Of course the driver can still tweak and 605override these activities. 606 607Note that the information that controls this behaviour is in the bus's 608driver, not the child's. In fact it is possible that child has no knowledge 609that it is connected to a bus. The same child device may even be used on two 610different bus types. As an example. the 'flash' device shown above may also 611be connected on a SATA bus or standalone with no bus:: 612 613 xhci_usb (UCLASS_USB) 614 flash (UCLASS_FLASH_STORAGE) - parent data/methods defined by USB bus 615 616 sata (UCLASS_SATA) 617 flash (UCLASS_FLASH_STORAGE) - parent data/methods defined by SATA bus 618 619 flash (UCLASS_FLASH_STORAGE) - no parent data/methods (not on a bus) 620 621Above you can see that the driver for xhci_usb/sata controls the child's 622bus methods. In the third example the device is not on a bus, and therefore 623will not have these methods at all. Consider the case where the flash 624device defines child methods. These would be used for *its* children, and 625would be quite separate from the methods defined by the driver for the bus 626that the flash device is connetced to. The act of attaching a device to a 627parent device which is a bus, causes the device to start behaving like a 628bus device, regardless of its own views on the matter. 629 630The uclass for the device can also contain data private to that uclass. 631But note that each device on the bus may be a memeber of a different 632uclass, and this data has nothing to do with the child data for each child 633on the bus. It is the bus' uclass that controls the child with respect to 634the bus. 635 636 637Driver Lifecycle 638---------------- 639 640Here are the stages that a device goes through in driver model. Note that all 641methods mentioned here are optional - e.g. if there is no probe() method for 642a device then it will not be called. A simple device may have very few 643methods actually defined. 644 645Bind stage 646^^^^^^^^^^ 647 648U-Boot discovers devices using one of these two methods: 649 650- Scan the U_BOOT_DEVICE() definitions. U-Boot looks up the name specified 651 by each, to find the appropriate U_BOOT_DRIVER() definition. In this case, 652 there is no path by which driver_data may be provided, but the U_BOOT_DEVICE() 653 may provide platdata. 654 655- Scan through the device tree definitions. U-Boot looks at top-level 656 nodes in the the device tree. It looks at the compatible string in each node 657 and uses the of_match table of the U_BOOT_DRIVER() structure to find the 658 right driver for each node. In this case, the of_match table may provide a 659 driver_data value, but platdata cannot be provided until later. 660 661For each device that is discovered, U-Boot then calls device_bind() to create a 662new device, initializes various core fields of the device object such as name, 663uclass & driver, initializes any optional fields of the device object that are 664applicable such as of_offset, driver_data & platdata, and finally calls the 665driver's bind() method if one is defined. 666 667At this point all the devices are known, and bound to their drivers. There 668is a 'struct udevice' allocated for all devices. However, nothing has been 669activated (except for the root device). Each bound device that was created 670from a U_BOOT_DEVICE() declaration will hold the platdata pointer specified 671in that declaration. For a bound device created from the device tree, 672platdata will be NULL, but of_offset will be the offset of the device tree 673node that caused the device to be created. The uclass is set correctly for 674the device. 675 676The device's bind() method is permitted to perform simple actions, but 677should not scan the device tree node, not initialise hardware, nor set up 678structures or allocate memory. All of these tasks should be left for 679the probe() method. 680 681Note that compared to Linux, U-Boot's driver model has a separate step of 682probe/remove which is independent of bind/unbind. This is partly because in 683U-Boot it may be expensive to probe devices and we don't want to do it until 684they are needed, or perhaps until after relocation. 685 686Activation/probe 687^^^^^^^^^^^^^^^^ 688 689When a device needs to be used, U-Boot activates it, by following these 690steps (see device_probe()): 691 692 1. If priv_auto_alloc_size is non-zero, then the device-private space 693 is allocated for the device and zeroed. It will be accessible as 694 dev->priv. The driver can put anything it likes in there, but should use 695 it for run-time information, not platform data (which should be static 696 and known before the device is probed). 697 698 2. If platdata_auto_alloc_size is non-zero, then the platform data space 699 is allocated. This is only useful for device tree operation, since 700 otherwise you would have to specific the platform data in the 701 U_BOOT_DEVICE() declaration. The space is allocated for the device and 702 zeroed. It will be accessible as dev->platdata. 703 704 3. If the device's uclass specifies a non-zero per_device_auto_alloc_size, 705 then this space is allocated and zeroed also. It is allocated for and 706 stored in the device, but it is uclass data. owned by the uclass driver. 707 It is possible for the device to access it. 708 709 4. If the device's immediate parent specifies a per_child_auto_alloc_size 710 then this space is allocated. This is intended for use by the parent 711 device to keep track of things related to the child. For example a USB 712 flash stick attached to a USB host controller would likely use this 713 space. The controller can hold information about the USB state of each 714 of its children. 715 716 5. All parent devices are probed. It is not possible to activate a device 717 unless its predecessors (all the way up to the root device) are activated. 718 This means (for example) that an I2C driver will require that its bus 719 be activated. 720 721 6. The device's sequence number is assigned, either the requested one 722 (assuming no conflicts) or the next available one if there is a conflict 723 or nothing particular is requested. 724 725 7. If the driver provides an ofdata_to_platdata() method, then this is 726 called to convert the device tree data into platform data. This should 727 do various calls like fdtdec_get_int(gd->fdt_blob, dev_of_offset(dev), ...) 728 to access the node and store the resulting information into dev->platdata. 729 After this point, the device works the same way whether it was bound 730 using a device tree node or U_BOOT_DEVICE() structure. In either case, 731 the platform data is now stored in the platdata structure. Typically you 732 will use the platdata_auto_alloc_size feature to specify the size of the 733 platform data structure, and U-Boot will automatically allocate and zero 734 it for you before entry to ofdata_to_platdata(). But if not, you can 735 allocate it yourself in ofdata_to_platdata(). Note that it is preferable 736 to do all the device tree decoding in ofdata_to_platdata() rather than 737 in probe(). (Apart from the ugliness of mixing configuration and run-time 738 data, one day it is possible that U-Boot will cache platform data for 739 devices which are regularly de/activated). 740 741 8. The device's probe() method is called. This should do anything that 742 is required by the device to get it going. This could include checking 743 that the hardware is actually present, setting up clocks for the 744 hardware and setting up hardware registers to initial values. The code 745 in probe() can access: 746 747 - platform data in dev->platdata (for configuration) 748 - private data in dev->priv (for run-time state) 749 - uclass data in dev->uclass_priv (for things the uclass stores 750 about this device) 751 752 Note: If you don't use priv_auto_alloc_size then you will need to 753 allocate the priv space here yourself. The same applies also to 754 platdata_auto_alloc_size. Remember to free them in the remove() method. 755 756 9. The device is marked 'activated' 757 758 10. The uclass's post_probe() method is called, if one exists. This may 759 cause the uclass to do some housekeeping to record the device as 760 activated and 'known' by the uclass. 761 762Running stage 763^^^^^^^^^^^^^ 764 765The device is now activated and can be used. From now until it is removed 766all of the above structures are accessible. The device appears in the 767uclass's list of devices (so if the device is in UCLASS_GPIO it will appear 768as a device in the GPIO uclass). This is the 'running' state of the device. 769 770Removal stage 771^^^^^^^^^^^^^ 772 773When the device is no-longer required, you can call device_remove() to 774remove it. This performs the probe steps in reverse: 775 776 1. The uclass's pre_remove() method is called, if one exists. This may 777 cause the uclass to do some housekeeping to record the device as 778 deactivated and no-longer 'known' by the uclass. 779 780 2. All the device's children are removed. It is not permitted to have 781 an active child device with a non-active parent. This means that 782 device_remove() is called for all the children recursively at this point. 783 784 3. The device's remove() method is called. At this stage nothing has been 785 deallocated so platform data, private data and the uclass data will all 786 still be present. This is where the hardware can be shut down. It is 787 intended that the device be completely inactive at this point, For U-Boot 788 to be sure that no hardware is running, it should be enough to remove 789 all devices. 790 791 4. The device memory is freed (platform data, private data, uclass data, 792 parent data). 793 794 Note: Because the platform data for a U_BOOT_DEVICE() is defined with a 795 static pointer, it is not de-allocated during the remove() method. For 796 a device instantiated using the device tree data, the platform data will 797 be dynamically allocated, and thus needs to be deallocated during the 798 remove() method, either: 799 800 - if the platdata_auto_alloc_size is non-zero, the deallocation 801 happens automatically within the driver model core; or 802 803 - when platdata_auto_alloc_size is 0, both the allocation (in probe() 804 or preferably ofdata_to_platdata()) and the deallocation in remove() 805 are the responsibility of the driver author. 806 807 5. The device sequence number is set to -1, meaning that it no longer 808 has an allocated sequence. If the device is later reactivated and that 809 sequence number is still free, it may well receive the name sequence 810 number again. But from this point, the sequence number previously used 811 by this device will no longer exist (think of SPI bus 2 being removed 812 and bus 2 is no longer available for use). 813 814 6. The device is marked inactive. Note that it is still bound, so the 815 device structure itself is not freed at this point. Should the device be 816 activated again, then the cycle starts again at step 2 above. 817 818Unbind stage 819^^^^^^^^^^^^ 820 821The device is unbound. This is the step that actually destroys the device. 822If a parent has children these will be destroyed first. After this point 823the device does not exist and its memory has be deallocated. 824 825 826Data Structures 827--------------- 828 829Driver model uses a doubly-linked list as the basic data structure. Some 830nodes have several lists running through them. Creating a more efficient 831data structure might be worthwhile in some rare cases, once we understand 832what the bottlenecks are. 833 834 835Changes since v1 836---------------- 837 838For the record, this implementation uses a very similar approach to the 839original patches, but makes at least the following changes: 840 841- Tried to aggressively remove boilerplate, so that for most drivers there 842 is little or no 'driver model' code to write. 843- Moved some data from code into data structure - e.g. store a pointer to 844 the driver operations structure in the driver, rather than passing it 845 to the driver bind function. 846- Rename some structures to make them more similar to Linux (struct udevice 847 instead of struct instance, struct platdata, etc.) 848- Change the name 'core' to 'uclass', meaning U-Boot class. It seems that 849 this concept relates to a class of drivers (or a subsystem). We shouldn't 850 use 'class' since it is a C++ reserved word, so U-Boot class (uclass) seems 851 better than 'core'. 852- Remove 'struct driver_instance' and just use a single 'struct udevice'. 853 This removes a level of indirection that doesn't seem necessary. 854- Built in device tree support, to avoid the need for platdata 855- Removed the concept of driver relocation, and just make it possible for 856 the new driver (created after relocation) to access the old driver data. 857 I feel that relocation is a very special case and will only apply to a few 858 drivers, many of which can/will just re-init anyway. So the overhead of 859 dealing with this might not be worth it. 860- Implemented a GPIO system, trying to keep it simple 861 862 863Pre-Relocation Support 864---------------------- 865 866For pre-relocation we simply call the driver model init function. Only 867drivers marked with DM_FLAG_PRE_RELOC or the device tree 'u-boot,dm-pre-reloc' 868property are initialised prior to relocation. This helps to reduce the driver 869model overhead. This flag applies to SPL and TPL as well, if device tree is 870enabled (CONFIG_OF_CONTROL) there. 871 872Note when device tree is enabled, the device tree 'u-boot,dm-pre-reloc' 873property can provide better control granularity on which device is bound 874before relocation. While with DM_FLAG_PRE_RELOC flag of the driver all 875devices with the same driver are bound, which requires allocation a large 876amount of memory. When device tree is not used, DM_FLAG_PRE_RELOC is the 877only way for statically declared devices via U_BOOT_DEVICE() to be bound 878prior to relocation. 879 880It is possible to limit this to specific relocation steps, by using 881the more specialized 'u-boot,dm-spl' and 'u-boot,dm-tpl' flags 882in the device tree node. For U-Boot proper you can use 'u-boot,dm-pre-proper' 883which means that it will be processed (and a driver bound) in U-Boot proper 884prior to relocation, but will not be available in SPL or TPL. 885 886To reduce the size of SPL and TPL, only the nodes with pre-relocation properties 887('u-boot,dm-pre-reloc', 'u-boot,dm-spl' or 'u-boot,dm-tpl') are keept in their 888device trees (see README.SPL for details); the remaining nodes are always bound. 889 890Then post relocation we throw that away and re-init driver model again. 891For drivers which require some sort of continuity between pre- and 892post-relocation devices, we can provide access to the pre-relocation 893device pointers, but this is not currently implemented (the root device 894pointer is saved but not made available through the driver model API). 895 896 897SPL Support 898----------- 899 900Driver model can operate in SPL. Its efficient implementation and small code 901size provide for a small overhead which is acceptable for all but the most 902constrained systems. 903 904To enable driver model in SPL, define CONFIG_SPL_DM. You might want to 905consider the following option also. See the main README for more details. 906 907 - CONFIG_SYS_MALLOC_SIMPLE 908 - CONFIG_DM_WARN 909 - CONFIG_DM_DEVICE_REMOVE 910 - CONFIG_DM_STDIO 911 912 913Enabling Driver Model 914--------------------- 915 916Driver model is being brought into U-Boot gradually. As each subsystems gets 917support, a uclass is created and a CONFIG to enable use of driver model for 918that subsystem. 919 920For example CONFIG_DM_SERIAL enables driver model for serial. With that 921defined, the old serial support is not enabled, and your serial driver must 922conform to driver model. With that undefined, the old serial support is 923enabled and driver model is not available for serial. This means that when 924you convert a driver, you must either convert all its boards, or provide for 925the driver to be compiled both with and without driver model (generally this 926is not very hard). 927 928See the main README for full details of the available driver model CONFIG 929options. 930 931 932Things to punt for later 933------------------------ 934 935Uclasses are statically numbered at compile time. It would be possible to 936change this to dynamic numbering, but then we would require some sort of 937lookup service, perhaps searching by name. This is slightly less efficient 938so has been left out for now. One small advantage of dynamic numbering might 939be fewer merge conflicts in uclass-id.h. 940