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
13struct 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
21static 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
27static 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
34static 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
43static 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 */
80int 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