[PATCH v3 1/5] drm/i915: Add support for panels with VESA backlights with PWM enable/disable

This simply adds proper support for panel backlights that can be controlled
via VESA's backlight control protocol, but which also require that we
enable and disable the backlight via PWM instead of via the DPCD interface.
We also enable this by default, in order to fix some people's backlights
that were broken by not having this enabled.

For reference, backlights that require this and use VESA's backlight
interface tend to be laptops with hybrid GPUs, but this very well may
change in the future.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://gitlab.freedesktop.org/drm/intel/-/issues/3680
Fixes: fe7d52bccab6 ("drm/i915/dp: Don't use DPCD backlights that need PWM enable/disable")
Cc: <redacted> # v5.12+
---
 .../drm/i915/display/intel_dp_aux_backlight.c | 24 ++++++++++++++-----
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
index 569d17b4d00f..594fdc7453ca 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c

@@ -293,6 +293,10 @@ intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
 	struct intel_panel *panel = &connector->panel;
 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
 
+	if (!panel->backlight.edp.vesa.info.aux_enable)
+		panel->backlight.pwm_funcs->enable(crtc_state, conn_state,
+						   panel->backlight.pwm_level_max);
+
 	drm_edp_backlight_enable(&intel_dp->aux, &panel->backlight.edp.vesa.info, level);
 }
 

@@ -304,6 +308,10 @@ static void intel_dp_aux_vesa_disable_backlight(const struct drm_connector_state
 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
 
 	drm_edp_backlight_disable(&intel_dp->aux, &panel->backlight.edp.vesa.info);
+
+	if (!panel->backlight.edp.vesa.info.aux_enable)
+		panel->backlight.pwm_funcs->disable(old_conn_state,
+						    intel_backlight_invert_pwm_level(connector, 0));
 }
 
 static int intel_dp_aux_vesa_setup_backlight(struct intel_connector *connector, enum pipe pipe)

@@ -321,6 +329,15 @@ static int intel_dp_aux_vesa_setup_backlight(struct intel_connector *connector,
 	if (ret < 0)
 		return ret;
 
+	if (!panel->backlight.edp.vesa.info.aux_enable) {
+		ret = panel->backlight.pwm_funcs->setup(connector, pipe);
+		if (ret < 0) {
+			drm_err(&i915->drm,
+				"Failed to setup PWM backlight controls for eDP backlight: %d\n",
+				ret);
+			return ret;
+		}
+	}
 	panel->backlight.max = panel->backlight.edp.vesa.info.max;
 	panel->backlight.min = 0;
 	if (current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {

@@ -340,12 +357,7 @@ intel_dp_aux_supports_vesa_backlight(struct intel_connector *connector)
 	struct intel_dp *intel_dp = intel_attached_dp(connector);
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 
-	/* TODO: We currently only support AUX only backlight configurations, not backlights which
-	 * require a mix of PWM and AUX controls to work. In the mean time, these machines typically
-	 * work just fine using normal PWM controls anyway.
-	 */
-	if ((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
-	    drm_edp_backlight_supported(intel_dp->edp_dpcd)) {
+	if (drm_edp_backlight_supported(intel_dp->edp_dpcd)) {
 		drm_dbg_kms(&i915->drm, "AUX Backlight Control Supported!\n");
 		return true;
 	}

-- 
2.31.1

On Tue, Oct 05, 2021 at 10:40:14PM -0400, Lyude Paul wrote:

What't the story here with the non-inverted max vs. pontetially inverted
0 in the counterpart?

-- 
Ville Syrjälä
Intel

On Tue, 2021-10-19 at 21:09 +0300, Ville Syrjälä wrote:

On Tue, Oct 05, 2021 at 10:40:14PM -0400, Lyude Paul wrote:

quoted

This simply adds proper support for panel backlights that can be
controlled
via VESA's backlight control protocol, but which also require that we
enable and disable the backlight via PWM instead of via the DPCD
interface.
We also enable this by default, in order to fix some people's backlights
that were broken by not having this enabled.

For reference, backlights that require this and use VESA's backlight
interface tend to be laptops with hybrid GPUs, but this very well may
change in the future.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://gitlab.freedesktop.org/drm/intel/-/issues/3680
Fixes: fe7d52bccab6 ("drm/i915/dp: Don't use DPCD backlights that need PWM
enable/disable")
Cc: <redacted> # v5.12+
---
 .../drm/i915/display/intel_dp_aux_backlight.c | 24 ++++++++++++++-----
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c

b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
index 569d17b4d00f..594fdc7453ca 100644

--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c

@@ -293,6 +293,10 @@ intel_dp_aux_vesa_enable_backlight(const struct

intel_crtc_state *crtc_state,
        struct intel_panel *panel = &connector->panel;
        struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
 
+       if (!panel->backlight.edp.vesa.info.aux_enable)
+               panel->backlight.pwm_funcs->enable(crtc_state, conn_state,
+                                                  panel-

quoted

backlight.pwm_level_max);

What't the story here with the non-inverted max vs. pontetially inverted
0 in the counterpart?

OH! Nice catch,  I wonder if this explains some of the weirdness with samus-
fi-bdw…

Anyway-unfortunately I don't know the precise answer to if we're supposed to
be inverting the panel backlight level or not, so I'd say we should probably
just go with whatever the Intel HDR AUX interface is currently doing - which
is inverting the panel PWM level when needed. Will fix this in a respin
shortly

quoted

+
        drm_edp_backlight_enable(&intel_dp->aux, &panel-

quoted

backlight.edp.vesa.info, level);

 }
 

@@ -304,6 +308,10 @@ static void intel_dp_aux_vesa_disable_backlight(const

struct drm_connector_state
        struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
 
        drm_edp_backlight_disable(&intel_dp->aux, &panel-

quoted

backlight.edp.vesa.info);

+
+       if (!panel->backlight.edp.vesa.info.aux_enable)
+               panel->backlight.pwm_funcs->disable(old_conn_state,
+                                                  
intel_backlight_invert_pwm_level(connector, 0));
 }
 
 static int intel_dp_aux_vesa_setup_backlight(struct intel_connector
*connector, enum pipe pipe)

@@ -321,6 +329,15 @@ static int intel_dp_aux_vesa_setup_backlight(struct

intel_connector *connector,
        if (ret < 0)
                return ret;
 
+       if (!panel->backlight.edp.vesa.info.aux_enable) {
+               ret = panel->backlight.pwm_funcs->setup(connector, pipe);
+               if (ret < 0) {
+                       drm_err(&i915->drm,
+                               "Failed to setup PWM backlight controls
for eDP backlight: %d\n",
+                               ret);
+                       return ret;
+               }
+       }
        panel->backlight.max = panel->backlight.edp.vesa.info.max;
        panel->backlight.min = 0;
        if (current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {

@@ -340,12 +357,7 @@ intel_dp_aux_supports_vesa_backlight(struct

intel_connector *connector)
        struct intel_dp *intel_dp = intel_attached_dp(connector);
        struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 
-       /* TODO: We currently only support AUX only backlight
configurations, not backlights which
-        * require a mix of PWM and AUX controls to work. In the mean
time, these machines typically
-        * work just fine using normal PWM controls anyway.
-        */
-       if ((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
-           drm_edp_backlight_supported(intel_dp->edp_dpcd)) {
+       if (drm_edp_backlight_supported(intel_dp->edp_dpcd)) {
                drm_dbg_kms(&i915->drm, "AUX Backlight Control
Supported!\n");
                return true;
        }
-- 
2.31.1

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat