[Intel-gfx] [PATCH 1/5] drm/i915: Fix condition check for backlight control via DPCD

[Puthikorn Voravootivat]

Currently the intel_dp_aux_backlight driver requires eDP panel
to support these conditions to allow the backlight adjust via
dpcd register.
1) DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP
2) DP_EDP_BACKLIGHT_AUX_ENABLE_CAP
3) not DP_EDP_BACKLIGHT_PIN_ENABLE_CAP
4) not DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP

Condition 2,3,4 are incorect because of the following reasons.
For 2), "backlight can be enabled via AUX" is not "brightness
can be adjusted via AUX". For 3) and 4), this requires panel
to not support backlight adjustment via eDP BL_PWM_DIM pin,
but there are some panels that support both AUX and eDP pin.

This patch fixes the condition by checking for these instead.
1) DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP
2) DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP

This patch also add a check to DP_EDP_BACKLIGHT_AUX_ENABLE_CAP
in set_aux_backlight_enable() since the backlight enablement
can be done via BL_ENABLE eDP connector pin in the case that
it does not support doing that via AUX.

Signed-off-by: Puthikorn Voravootivat <puthik at chromium.org>
---
 drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
index 6532e226db29..abfb09c1269f 100644
--- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
@@ -28,6 +28,10 @@ static void set_aux_backlight_enable(struct intel_dp *intel_dp, bool enable)
 {
 	uint8_t reg_val = 0;
 
+	/* Early return when display use other mechanism to enable backlight. */
+	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP))
+		return;
+
 	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
 			      &reg_val) < 0) {
 		DRM_DEBUG_KMS("Failed to read DPCD register 0x%x\n",
@@ -142,10 +146,8 @@ intel_dp_aux_display_control_capable(struct intel_connector *connector)
 	/* Check the  eDP Display control capabilities registers to determine if
 	 * the panel can support backlight control over the aux channel
 	 */
-	if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
-	    (intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
-	    !((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_PIN_ENABLE_CAP) ||
-	      (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP))) {
+	if ((intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
+	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP)) {
 		DRM_DEBUG_KMS("AUX Backlight Control Supported!\n");
 		return true;
 	}
-- 
2.12.0.246.ga2ecc84866-goog