1 /*
2 * Thunderbolt Cactus Ridge driver - capabilities lookup
3 *
4 * Copyright (c) 2014 Andreas Noever <andreas.noever@gmail.com>
5 */
6
7 #include <linux/slab.h>
8 #include <linux/errno.h>
9
10 #include "tb.h"
11
12
13 struct tb_cap_any {
14 union {
15 struct tb_cap_basic basic;
16 struct tb_cap_extended_short extended_short;
17 struct tb_cap_extended_long extended_long;
18 };
19 } __packed;
20
tb_cap_is_basic(struct tb_cap_any * cap)21 static bool tb_cap_is_basic(struct tb_cap_any *cap)
22 {
23 /* basic.cap is u8. This checks only the lower 8 bit of cap. */
24 return cap->basic.cap != 5;
25 }
26
tb_cap_is_long(struct tb_cap_any * cap)27 static bool tb_cap_is_long(struct tb_cap_any *cap)
28 {
29 return !tb_cap_is_basic(cap)
30 && cap->extended_short.next == 0
31 && cap->extended_short.length == 0;
32 }
33
tb_cap(struct tb_cap_any * cap)34 static enum tb_cap tb_cap(struct tb_cap_any *cap)
35 {
36 if (tb_cap_is_basic(cap))
37 return cap->basic.cap;
38 else
39 /* extended_short/long have cap at the same offset. */
40 return cap->extended_short.cap;
41 }
42
tb_cap_next(struct tb_cap_any * cap,u32 offset)43 static u32 tb_cap_next(struct tb_cap_any *cap, u32 offset)
44 {
45 int next;
46 if (offset == 1) {
47 /*
48 * The first pointer is part of the switch header and always
49 * a simple pointer.
50 */
51 next = cap->basic.next;
52 } else {
53 /*
54 * Somehow Intel decided to use 3 different types of capability
55 * headers. It is not like anyone could have predicted that
56 * single byte offsets are not enough...
57 */
58 if (tb_cap_is_basic(cap))
59 next = cap->basic.next;
60 else if (!tb_cap_is_long(cap))
61 next = cap->extended_short.next;
62 else
63 next = cap->extended_long.next;
64 }
65 /*
66 * "Hey, we could terminate some capability lists with a null offset
67 * and others with a pointer to the last element." - "Great idea!"
68 */
69 if (next == offset)
70 return 0;
71 return next;
72 }
73
74 /**
75 * tb_find_cap() - find a capability
76 *
77 * Return: Returns a positive offset if the capability was found and 0 if not.
78 * Returns an error code on failure.
79 */
tb_find_cap(struct tb_port * port,enum tb_cfg_space space,enum tb_cap cap)80 int tb_find_cap(struct tb_port *port, enum tb_cfg_space space, enum tb_cap cap)
81 {
82 u32 offset = 1;
83 struct tb_cap_any header;
84 int res;
85 int retries = 10;
86 while (retries--) {
87 res = tb_port_read(port, &header, space, offset, 1);
88 if (res) {
89 /* Intel needs some help with linked lists. */
90 if (space == TB_CFG_PORT && offset == 0xa
91 && port->config.type == TB_TYPE_DP_HDMI_OUT) {
92 offset = 0x39;
93 continue;
94 }
95 return res;
96 }
97 if (offset != 1) {
98 if (tb_cap(&header) == cap)
99 return offset;
100 if (tb_cap_is_long(&header)) {
101 /* tb_cap_extended_long is 2 dwords */
102 res = tb_port_read(port, &header, space,
103 offset, 2);
104 if (res)
105 return res;
106 }
107 }
108 offset = tb_cap_next(&header, offset);
109 if (!offset)
110 return 0;
111 }
112 tb_port_WARN(port,
113 "run out of retries while looking for cap %#x in config space %d, last offset: %#x\n",
114 cap, space, offset);
115 return -EIO;
116 }
117