[RFC v2 1/8] drm/i915/dp: Program source OUI on eDP panels

[Lyude Paul]

Since we're about to start adding support for Intel's magic HDR
backlight interface over DPCD, we need to ensure we're properly
programming this field so that Intel specific sink services are exposed.
Otherwise, 0x300-0x3ff will just read zeroes.

We also take care not to reprogram the source OUI if it already matches
what we expect. This is just to be careful so that we don't accidentally
take the panel out of any backlight control modes we found it in.

v2:
* Add careful parameter to intel_edp_init_source_oui() to avoid
  re-writing the source OUI if it's already been set during driver
  initialization

Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
Cc: thaytan@xxxxxxxxxxxx
Cc: Vasily Khoruzhick <anarsoul@xxxxxxxxx>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 33 +++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 4bd10456ad188..7db2b6a3cd52e 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -3424,6 +3424,29 @@ void intel_dp_sink_set_decompression_state(struct intel_dp *intel_dp,
 			    enable ? "enable" : "disable");
 }
 
+static void
+intel_edp_init_source_oui(struct intel_dp *intel_dp, bool careful)
+{
+	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+	u8 oui[] = { 0x00, 0xaa, 0x01 };
+	u8 buf[3] = { 0 };
+
+	/*
+	 * During driver init, we want to be careful and avoid changing the source OUI if it's
+	 * already set to what we want, so as to avoid clearing any state by accident
+	 */
+	if (careful) {
+		if (drm_dp_dpcd_read(&intel_dp->aux, DP_SOURCE_OUI, buf, sizeof(buf)) < 0)
+			drm_err(&i915->drm, "Failed to read source OUI\n");
+
+		if (memcmp(oui, buf, sizeof(oui)) == 0)
+			return;
+	}
+
+	if (drm_dp_dpcd_write(&intel_dp->aux, DP_SOURCE_OUI, oui, sizeof(oui)) < 0)
+		drm_err(&i915->drm, "Failed to write source OUI\n");
+}
+
 /* If the sink supports it, try to set the power state appropriately */
 void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode)
 {
@@ -3443,6 +3466,10 @@ void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode)
 	} else {
 		struct intel_lspcon *lspcon = dp_to_lspcon(intel_dp);
 
+		/* Write the source OUI as early as possible */
+		if (intel_dp_is_edp(intel_dp))
+			intel_edp_init_source_oui(intel_dp, false);
+
 		/*
 		 * When turning on, we need to retry for 1ms to give the sink
 		 * time to wake up.
@@ -4607,6 +4634,12 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
 	if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv))
 		intel_dp_get_dsc_sink_cap(intel_dp);
 
+	/*
+	 * If needed, program our source OUI so we can make various Intel-specific AUX services
+	 * available (such as HDR backlight controls)
+	 */
+	intel_edp_init_source_oui(intel_dp, true);
+
 	return true;
 }
 
-- 
2.26.2