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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