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}