1 2------- 3PHY Abstraction Layer 4(Updated 2008-04-08) 5 6Purpose 7 8 Most network devices consist of set of registers which provide an interface 9 to a MAC layer, which communicates with the physical connection through a 10 PHY. The PHY concerns itself with negotiating link parameters with the link 11 partner on the other side of the network connection (typically, an ethernet 12 cable), and provides a register interface to allow drivers to determine what 13 settings were chosen, and to configure what settings are allowed. 14 15 While these devices are distinct from the network devices, and conform to a 16 standard layout for the registers, it has been common practice to integrate 17 the PHY management code with the network driver. This has resulted in large 18 amounts of redundant code. Also, on embedded systems with multiple (and 19 sometimes quite different) ethernet controllers connected to the same 20 management bus, it is difficult to ensure safe use of the bus. 21 22 Since the PHYs are devices, and the management busses through which they are 23 accessed are, in fact, busses, the PHY Abstraction Layer treats them as such. 24 In doing so, it has these goals: 25 26 1) Increase code-reuse 27 2) Increase overall code-maintainability 28 3) Speed development time for new network drivers, and for new systems 29 30 Basically, this layer is meant to provide an interface to PHY devices which 31 allows network driver writers to write as little code as possible, while 32 still providing a full feature set. 33 34The MDIO bus 35 36 Most network devices are connected to a PHY by means of a management bus. 37 Different devices use different busses (though some share common interfaces). 38 In order to take advantage of the PAL, each bus interface needs to be 39 registered as a distinct device. 40 41 1) read and write functions must be implemented. Their prototypes are: 42 43 int write(struct mii_bus *bus, int mii_id, int regnum, u16 value); 44 int read(struct mii_bus *bus, int mii_id, int regnum); 45 46 mii_id is the address on the bus for the PHY, and regnum is the register 47 number. These functions are guaranteed not to be called from interrupt 48 time, so it is safe for them to block, waiting for an interrupt to signal 49 the operation is complete 50 51 2) A reset function is necessary. This is used to return the bus to an 52 initialized state. 53 54 3) A probe function is needed. This function should set up anything the bus 55 driver needs, setup the mii_bus structure, and register with the PAL using 56 mdiobus_register. Similarly, there's a remove function to undo all of 57 that (use mdiobus_unregister). 58 59 4) Like any driver, the device_driver structure must be configured, and init 60 exit functions are used to register the driver. 61 62 5) The bus must also be declared somewhere as a device, and registered. 63 64 As an example for how one driver implemented an mdio bus driver, see 65 drivers/net/ethernet/freescale/fsl_pq_mdio.c and an associated DTS file 66 for one of the users. (e.g. "git grep fsl,.*-mdio arch/powerpc/boot/dts/") 67 68Connecting to a PHY 69 70 Sometime during startup, the network driver needs to establish a connection 71 between the PHY device, and the network device. At this time, the PHY's bus 72 and drivers need to all have been loaded, so it is ready for the connection. 73 At this point, there are several ways to connect to the PHY: 74 75 1) The PAL handles everything, and only calls the network driver when 76 the link state changes, so it can react. 77 78 2) The PAL handles everything except interrupts (usually because the 79 controller has the interrupt registers). 80 81 3) The PAL handles everything, but checks in with the driver every second, 82 allowing the network driver to react first to any changes before the PAL 83 does. 84 85 4) The PAL serves only as a library of functions, with the network device 86 manually calling functions to update status, and configure the PHY 87 88 89Letting the PHY Abstraction Layer do Everything 90 91 If you choose option 1 (The hope is that every driver can, but to still be 92 useful to drivers that can't), connecting to the PHY is simple: 93 94 First, you need a function to react to changes in the link state. This 95 function follows this protocol: 96 97 static void adjust_link(struct net_device *dev); 98 99 Next, you need to know the device name of the PHY connected to this device. 100 The name will look something like, "0:00", where the first number is the 101 bus id, and the second is the PHY's address on that bus. Typically, 102 the bus is responsible for making its ID unique. 103 104 Now, to connect, just call this function: 105 106 phydev = phy_connect(dev, phy_name, &adjust_link, interface); 107 108 phydev is a pointer to the phy_device structure which represents the PHY. If 109 phy_connect is successful, it will return the pointer. dev, here, is the 110 pointer to your net_device. Once done, this function will have started the 111 PHY's software state machine, and registered for the PHY's interrupt, if it 112 has one. The phydev structure will be populated with information about the 113 current state, though the PHY will not yet be truly operational at this 114 point. 115 116 PHY-specific flags should be set in phydev->dev_flags prior to the call 117 to phy_connect() such that the underlying PHY driver can check for flags 118 and perform specific operations based on them. 119 This is useful if the system has put hardware restrictions on 120 the PHY/controller, of which the PHY needs to be aware. 121 122 interface is a u32 which specifies the connection type used 123 between the controller and the PHY. Examples are GMII, MII, 124 RGMII, and SGMII. For a full list, see include/linux/phy.h 125 126 Now just make sure that phydev->supported and phydev->advertising have any 127 values pruned from them which don't make sense for your controller (a 10/100 128 controller may be connected to a gigabit capable PHY, so you would need to 129 mask off SUPPORTED_1000baseT*). See include/linux/ethtool.h for definitions 130 for these bitfields. Note that you should not SET any bits, or the PHY may 131 get put into an unsupported state. 132 133 Lastly, once the controller is ready to handle network traffic, you call 134 phy_start(phydev). This tells the PAL that you are ready, and configures the 135 PHY to connect to the network. If you want to handle your own interrupts, 136 just set phydev->irq to PHY_IGNORE_INTERRUPT before you call phy_start. 137 Similarly, if you don't want to use interrupts, set phydev->irq to PHY_POLL. 138 139 When you want to disconnect from the network (even if just briefly), you call 140 phy_stop(phydev). 141 142Keeping Close Tabs on the PAL 143 144 It is possible that the PAL's built-in state machine needs a little help to 145 keep your network device and the PHY properly in sync. If so, you can 146 register a helper function when connecting to the PHY, which will be called 147 every second before the state machine reacts to any changes. To do this, you 148 need to manually call phy_attach() and phy_prepare_link(), and then call 149 phy_start_machine() with the second argument set to point to your special 150 handler. 151 152 Currently there are no examples of how to use this functionality, and testing 153 on it has been limited because the author does not have any drivers which use 154 it (they all use option 1). So Caveat Emptor. 155 156Doing it all yourself 157 158 There's a remote chance that the PAL's built-in state machine cannot track 159 the complex interactions between the PHY and your network device. If this is 160 so, you can simply call phy_attach(), and not call phy_start_machine or 161 phy_prepare_link(). This will mean that phydev->state is entirely yours to 162 handle (phy_start and phy_stop toggle between some of the states, so you 163 might need to avoid them). 164 165 An effort has been made to make sure that useful functionality can be 166 accessed without the state-machine running, and most of these functions are 167 descended from functions which did not interact with a complex state-machine. 168 However, again, no effort has been made so far to test running without the 169 state machine, so tryer beware. 170 171 Here is a brief rundown of the functions: 172 173 int phy_read(struct phy_device *phydev, u16 regnum); 174 int phy_write(struct phy_device *phydev, u16 regnum, u16 val); 175 176 Simple read/write primitives. They invoke the bus's read/write function 177 pointers. 178 179 void phy_print_status(struct phy_device *phydev); 180 181 A convenience function to print out the PHY status neatly. 182 183 int phy_start_interrupts(struct phy_device *phydev); 184 int phy_stop_interrupts(struct phy_device *phydev); 185 186 Requests the IRQ for the PHY interrupts, then enables them for 187 start, or disables then frees them for stop. 188 189 struct phy_device * phy_attach(struct net_device *dev, const char *phy_id, 190 phy_interface_t interface); 191 192 Attaches a network device to a particular PHY, binding the PHY to a generic 193 driver if none was found during bus initialization. 194 195 int phy_start_aneg(struct phy_device *phydev); 196 197 Using variables inside the phydev structure, either configures advertising 198 and resets autonegotiation, or disables autonegotiation, and configures 199 forced settings. 200 201 static inline int phy_read_status(struct phy_device *phydev); 202 203 Fills the phydev structure with up-to-date information about the current 204 settings in the PHY. 205 206 int phy_ethtool_sset(struct phy_device *phydev, struct ethtool_cmd *cmd); 207 int phy_ethtool_gset(struct phy_device *phydev, struct ethtool_cmd *cmd); 208 209 Ethtool convenience functions. 210 211 int phy_mii_ioctl(struct phy_device *phydev, 212 struct mii_ioctl_data *mii_data, int cmd); 213 214 The MII ioctl. Note that this function will completely screw up the state 215 machine if you write registers like BMCR, BMSR, ADVERTISE, etc. Best to 216 use this only to write registers which are not standard, and don't set off 217 a renegotiation. 218 219 220PHY Device Drivers 221 222 With the PHY Abstraction Layer, adding support for new PHYs is 223 quite easy. In some cases, no work is required at all! However, 224 many PHYs require a little hand-holding to get up-and-running. 225 226Generic PHY driver 227 228 If the desired PHY doesn't have any errata, quirks, or special 229 features you want to support, then it may be best to not add 230 support, and let the PHY Abstraction Layer's Generic PHY Driver 231 do all of the work. 232 233Writing a PHY driver 234 235 If you do need to write a PHY driver, the first thing to do is 236 make sure it can be matched with an appropriate PHY device. 237 This is done during bus initialization by reading the device's 238 UID (stored in registers 2 and 3), then comparing it to each 239 driver's phy_id field by ANDing it with each driver's 240 phy_id_mask field. Also, it needs a name. Here's an example: 241 242 static struct phy_driver dm9161_driver = { 243 .phy_id = 0x0181b880, 244 .name = "Davicom DM9161E", 245 .phy_id_mask = 0x0ffffff0, 246 ... 247 } 248 249 Next, you need to specify what features (speed, duplex, autoneg, 250 etc) your PHY device and driver support. Most PHYs support 251 PHY_BASIC_FEATURES, but you can look in include/mii.h for other 252 features. 253 254 Each driver consists of a number of function pointers: 255 256 config_init: configures PHY into a sane state after a reset. 257 For instance, a Davicom PHY requires descrambling disabled. 258 probe: Does any setup needed by the driver 259 suspend/resume: power management 260 config_aneg: Changes the speed/duplex/negotiation settings 261 read_status: Reads the current speed/duplex/negotiation settings 262 ack_interrupt: Clear a pending interrupt 263 config_intr: Enable or disable interrupts 264 remove: Does any driver take-down 265 266 Of these, only config_aneg and read_status are required to be 267 assigned by the driver code. The rest are optional. Also, it is 268 preferred to use the generic phy driver's versions of these two 269 functions if at all possible: genphy_read_status and 270 genphy_config_aneg. If this is not possible, it is likely that 271 you only need to perform some actions before and after invoking 272 these functions, and so your functions will wrap the generic 273 ones. 274 275 Feel free to look at the Marvell, Cicada, and Davicom drivers in 276 drivers/net/phy/ for examples (the lxt and qsemi drivers have 277 not been tested as of this writing) 278 279Board Fixups 280 281 Sometimes the specific interaction between the platform and the PHY requires 282 special handling. For instance, to change where the PHY's clock input is, 283 or to add a delay to account for latency issues in the data path. In order 284 to support such contingencies, the PHY Layer allows platform code to register 285 fixups to be run when the PHY is brought up (or subsequently reset). 286 287 When the PHY Layer brings up a PHY it checks to see if there are any fixups 288 registered for it, matching based on UID (contained in the PHY device's phy_id 289 field) and the bus identifier (contained in phydev->dev.bus_id). Both must 290 match, however two constants, PHY_ANY_ID and PHY_ANY_UID, are provided as 291 wildcards for the bus ID and UID, respectively. 292 293 When a match is found, the PHY layer will invoke the run function associated 294 with the fixup. This function is passed a pointer to the phy_device of 295 interest. It should therefore only operate on that PHY. 296 297 The platform code can either register the fixup using phy_register_fixup(): 298 299 int phy_register_fixup(const char *phy_id, 300 u32 phy_uid, u32 phy_uid_mask, 301 int (*run)(struct phy_device *)); 302 303 Or using one of the two stubs, phy_register_fixup_for_uid() and 304 phy_register_fixup_for_id(): 305 306 int phy_register_fixup_for_uid(u32 phy_uid, u32 phy_uid_mask, 307 int (*run)(struct phy_device *)); 308 int phy_register_fixup_for_id(const char *phy_id, 309 int (*run)(struct phy_device *)); 310 311 The stubs set one of the two matching criteria, and set the other one to 312 match anything. 313 314