[PATCH] [RFC] drm/i915/dp: add support for load detect Apple DP->VGA dongles

[Dave Airlie <airlied@gmail.com>]

From: Dave Airlie <airlied@redhat.com>

The DP1.2 spec has some bits for forced load sensing on VGA dongles,
however the apple dongle I have doesn't do DP 1.2 yet, so I dug into
its vendor specific area and found a register that seems to correspond
to load detected on the outputs.

The main reason I need this was at LCA this year the slide capture system
failed to provide EDID, but I realised OSX worked. Really need to add support
to nouveau, but hey i915 is a start.

The dongle also appears to use short IRQs to denote a plug/unplug event,
though something seems to be failing in reading back the dpcd values from it.
(also this is based on my MST work just because.)

Signed-off-by: Dave Airlie <airlied@redhat.com>
---
 drivers/gpu/drm/i915/intel_dp.c  | 29 +++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_drv.h |  1 +
 include/drm/drm_dp_helper.h      | 19 +++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index c500f63..49afd7d 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3173,6 +3173,16 @@ intel_dp_probe_oui(struct intel_dp *intel_dp)
 		DRM_DEBUG_KMS("Branch OUI: %02hx%02hx%02hx\n",
 			      buf[0], buf[1], buf[2]);
 
+	intel_dp->is_apple_vga = false;
+	if (drm_dp_branch_is_apple(buf)) {
+		u8 mybuf[8];
+		if (intel_dp_dpcd_read_wake(&intel_dp->aux, DP_BRANCH_OUI + 3, mybuf, 8)) {
+			if (drm_dp_apple_has_load_detect(mybuf)) {
+				DRM_DEBUG_KMS("detected Apple DP VGA dongle\n");
+				intel_dp->is_apple_vga = true;
+			}
+		}
+	}
 	edp_panel_vdd_off(intel_dp, false);
 }
 
@@ -3404,6 +3414,21 @@ intel_dp_detect_dpcd(struct intel_dp *intel_dp)
 	if (drm_probe_ddc(&intel_dp->aux.ddc))
 		return connector_status_connected;
 
+	if (intel_dp->is_apple_vga) {
+		u8 detect_buf;
+		int ret;
+		ret = drm_dp_dpcd_readb(&intel_dp->aux, DP_APPLE_LOAD_DETECT,
+					&detect_buf);
+
+		if (ret == 1) {
+			DRM_DEBUG_KMS("Apple VGA detect is 0x%x\n", detect_buf);
+			/* I suspect 4 == load, 8 == edid */
+			if (detect_buf)
+				return connector_status_connected;
+			else
+				return connector_status_disconnected;
+		}
+	}
 	/* Well we tried, say unknown for unreliable port types */
 	if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11) {
 		type = intel_dp->downstream_ports[0] & DP_DS_PORT_TYPE_MASK;
@@ -3854,6 +3879,10 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
 			 * but for short hpds we should check it now
 			 */
 			intel_dp_check_link_status(intel_dp);
+
+			/* if we get a short hpd on apple vga - its a hotplug */
+			if (intel_dp->is_apple_vga)
+				return true;
 		}
 	}
 	return false;
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 1edb38a..23f767c 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -549,6 +549,7 @@ struct intel_dp {
 	bool use_tps3;
 	bool can_mst; /* this port supports mst */
 	bool is_mst;
+	bool is_apple_vga;
 	int active_mst_links;
 	/* connector directly attached - won't be use for modeset in mst world */
 	struct intel_connector *attached_connector;
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 517d6c1..c8ebd27 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -612,4 +612,23 @@ int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link);
 int drm_dp_aux_register(struct drm_dp_aux *aux);
 void drm_dp_aux_unregister(struct drm_dp_aux *aux);
 
+#define DP_APPLE_OUI 0x10fa
+
+#define DP_APPLE_LOAD_DETECT (DP_BRANCH_OUI + 12)
+
+static inline bool drm_dp_branch_is_apple(const u8 buf[3])
+{
+	if (buf[0] == ((DP_APPLE_OUI >> 16) & 0xff) &&
+	    buf[1] == ((DP_APPLE_OUI >> 8) & 0xff) &&
+	    buf[2] == ((DP_APPLE_OUI & 0xff)))
+		return true;
+	return false;
+}
+
+static inline bool drm_dp_apple_has_load_detect(const u8 buf[8])
+{
+	if (!memcmp((const char *)buf, "mVGAa", 5))
+		return true;
+	return false;
+}
 #endif /* _DRM_DP_HELPER_H_ */
-- 
1.9.3