thunderbolt: Add thunderbolt capability handling

Thunderbolt config areas contain capability lists similar to those found
on pci devices. This patch introduces a tb_find_cap utility method to
search for capabilities.
Signed-off-by: Andreas Noever <andreas.noever@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/thunderbolt/Makefile

 obj-${CONFIG_THUNDERBOLT} := thunderbolt.o
-thunderbolt-objs := nhi.o ctl.o tb.o switch.o
+thunderbolt-objs := nhi.o ctl.o tb.o switch.o cap.o
 

drivers/thunderbolt/cap.c

+/*
+ * Thunderbolt Cactus Ridge driver - capabilities lookup
+ *
+ * Copyright (c) 2014 Andreas Noever <andreas.noever@gmail.com>
+ */
+
+#include <linux/slab.h>
+#include <linux/errno.h>
+
+#include "tb.h"
+
+
+struct tb_cap_any {
+	union {
+		struct tb_cap_basic basic;
+		struct tb_cap_extended_short extended_short;
+		struct tb_cap_extended_long extended_long;
+	};
+} __packed;
+
+static bool tb_cap_is_basic(struct tb_cap_any *cap)
+{
+	/* basic.cap is u8. This checks only the lower 8 bit of cap. */
+	return cap->basic.cap != 5;
+}
+
+static bool tb_cap_is_long(struct tb_cap_any *cap)
+{
+	return !tb_cap_is_basic(cap)
+	       && cap->extended_short.next == 0
+	       && cap->extended_short.length == 0;
+}
+
+static enum tb_cap tb_cap(struct tb_cap_any *cap)
+{
+	if (tb_cap_is_basic(cap))
+		return cap->basic.cap;
+	else
+		/* extended_short/long have cap at the same offset. */
+		return cap->extended_short.cap;
+}
+
+static u32 tb_cap_next(struct tb_cap_any *cap, u32 offset)
+{
+	int next;
+	if (offset == 1) {
+		/*
+		 * The first pointer is part of the switch header and always
+		 * a simple pointer.
+		 */
+		next = cap->basic.next;
+	} else {
+		/*
+		 * Somehow Intel decided to use 3 different types of capability
+		 * headers. It is not like anyone could have predicted that
+		 * single byte offsets are not enough...
+		 */
+		if (tb_cap_is_basic(cap))
+			next = cap->basic.next;
+		else if (!tb_cap_is_long(cap))
+			next = cap->extended_short.next;
+		else
+			next = cap->extended_long.next;
+	}
+	/*
+	 * "Hey, we could terminate some capability lists with a null offset
+	 *  and others with a pointer to the last element." - "Great idea!"
+	 */
+	if (next == offset)
+		return 0;
+	return next;
+}
+
+/**
+ * tb_find_cap() - find a capability
+ *
+ * Return: Returns a positive offset if the capability was found and 0 if not.
+ * Returns an error code on failure.
+ */
+int tb_find_cap(struct tb_port *port, enum tb_cfg_space space, enum tb_cap cap)
+{
+	u32 offset = 1;
+	struct tb_cap_any header;
+	int res;
+	int retries = 10;
+	while (retries--) {
+		res = tb_port_read(port, &header, space, offset, 1);
+		if (res) {
+			/* Intel needs some help with linked lists. */
+			if (space == TB_CFG_PORT && offset == 0xa
+			    && port->config.type == TB_TYPE_DP_HDMI_OUT) {
+				offset = 0x39;
+				continue;
+			}
+			return res;
+		}
+		if (offset != 1) {
+			if (tb_cap(&header) == cap)
+				return offset;
+			if (tb_cap_is_long(&header)) {
+				/* tb_cap_extended_long is 2 dwords */
+				res = tb_port_read(port, &header, space,
+						   offset, 2);
+				if (res)
+					return res;
+			}
+		}
+		offset = tb_cap_next(&header, offset);
+		if (!offset)
+			return 0;
+	}
+	tb_port_WARN(port,
+		     "run out of retries while looking for cap %#x in config space %d, last offset: %#x\n",
+		     cap, space, offset);
+	return -EIO;
+}

drivers/thunderbolt/tb.h

@@ -159,6 +159,8 @@ void thunderbolt_shutdown_and_free(struct tb *tb);
 struct tb_switch *tb_switch_alloc(struct tb *tb, u64 route);
 void tb_switch_free(struct tb_switch *sw);
 
+int tb_find_cap(struct tb_port *port, enum tb_cfg_space space, u32 value);
+
 
 static inline int tb_route_length(u64 route)
 {