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

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Date:   Tue, 19 Oct 2021 21:09:52 +0300
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Lyude Paul <lyude@...hat.com>
Cc:     intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        nouveau@...ts.freedesktop.org, stable@...r.kernel.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Sean Paul <seanpaul@...omium.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/5] drm/i915: Add support for panels with VESA
 backlights with PWM enable/disable

On Tue, Oct 05, 2021 at 10:40:14PM -0400, Lyude Paul wrote:
> 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@...hat.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: <stable@...r.kernel.org> # 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);

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

> +
>  	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

-- 
Ville Syrjälä
Intel