drm/dp/mst: dump branch OUI in debugfs (v2)

It appears some MST docks are worse than other, but the only
way to know is to see the sw revisions in here, so dump
the branch OUI so we can look at the sw revision.

v2: Thierry made me feel guilty, so I parsed the branch
OUI.
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -2631,6 +2631,16 @@ void drm_dp_mst_dump_topology(struct seq_file *m,
 			seq_printf(m, "%02x ", buf[i]);
 		seq_printf(m, "\n");
 
+		/* dump the standard OUI branch header */
+		ret = drm_dp_dpcd_read(mgr->aux, DP_BRANCH_OUI, buf, DP_BRANCH_OUI_HEADER_SIZE);
+		seq_printf(m, "branch oui: ");
+		for (i = 0; i < 0x3; i++)
+			seq_printf(m, "%02x", buf[i]);
+		seq_printf(m, " devid: ");
+		for (i = 0x3; i < 0x8; i++)
+			seq_printf(m, "%c", buf[i]);
+		seq_printf(m, " revision: hw: %x.%x sw: %x.%x", buf[0x9] >> 4, buf[0x9] & 0xf, buf[0xa], buf[0xb]);
+		seq_printf(m, "\n");
 		bret = dump_dp_payload_table(mgr, buf);
 		if (bret == true) {
 			seq_printf(m, "payload table: ");

include/drm/drm_dp_helper.h

@@ -578,6 +578,7 @@ u8 drm_dp_get_adjust_request_voltage(const u8 link_status[DP_LINK_STATUS_SIZE],
 u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SIZE],
 					  int lane);
 
+#define DP_BRANCH_OUI_HEADER_SIZE	0xc
 #define DP_RECEIVER_CAP_SIZE		0xf
 #define EDP_PSR_RECEIVER_CAP_SIZE	2