Re: [PATCH] drm/i915/backlight: Sanitize BIOS-enabled PCH PWM in full-AUX VESA path

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 13 May 2026, Suraj Kandpal <suraj.kandpal@intel.com> wrote:
> In full-AUX VESA mode (aux_enable && aux_set) the driver never touches
> the native PCH PWM. If BIOS left PWM CTL register enabled, the PCH PWM
> keeps system alive during s2idle and blocks S0ix.
> Always run pwm_funcs->setup() so pwm_enabled reflects real HW state,
> and on first enable in full-AUX mode call pwm_funcs->disable() once to
> clear the stale bit. Runtime behaviour is otherwise unchanged.
>
> Fixes: 40d2f5820951 ("drm/i915/backlight: Remove try_vesa_interface")
> Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
> ---
>  .../drm/i915/display/intel_dp_aux_backlight.c | 32 +++++++++++++------
>  1 file changed, 23 insertions(+), 9 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 a8d56ebf06a2..c828c568fb8b 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -496,6 +496,17 @@ 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);
>  
> +	/*
> +	 * In full AUX VESA mode the native PWM is never driven by us. If BIOS
> +	 * left it enabled, the PCH PWM keeps the system alive and blocks
> +	 * S0ix. Sanitize it once via pwm_funcs->disable.
> +	 */
> +	if (panel->backlight.edp.vesa.info.aux_enable &&
> +	    panel->backlight.edp.vesa.info.aux_set &&
> +	    panel->backlight.pwm_enabled)
> +		panel->backlight.pwm_funcs->disable(conn_state,
> +						    intel_backlight_invert_pwm_level(connector, 0));
> +
>  	if (!(panel->backlight.edp.vesa.info.aux_enable ||
>  	      panel->backlight.edp.vesa.info.luminance_set)) {
>  		u32 pwm_level;
> @@ -558,15 +569,18 @@ static int intel_dp_aux_vesa_setup_backlight(struct intel_connector *connector,
>  				    panel->backlight.edp.vesa.info.luminance_set),
>  		    backlight_unit_str(panel));
>  
> -	if (!panel->backlight.edp.vesa.info.aux_set ||
> -	    !panel->backlight.edp.vesa.info.aux_enable) {
> -		ret = panel->backlight.pwm_funcs->setup(connector, pipe);
> -		if (ret < 0) {
> -			drm_err(display->drm,
> -				"[CONNECTOR:%d:%s] Failed to setup PWM backlight controls for eDP backlight: %d\n",
> -				connector->base.base.id, connector->base.name, ret);
> -			return ret;
> -		}
> +	/*
> +	 * Always probe the native PWM HW state so panel->backlight.pwm_enabled
> +	 * reflects what BIOS left behind. Required for the full-AUX VESA path
> +	 * to detect and sanitize a BIOS-enabled PCH PWM that would otherwise
> +	 * block S0ix.
> +	 */
> +	ret = panel->backlight.pwm_funcs->setup(connector, pipe);

This will log something like "Using native PWM for backlight control" in
dmesg, which is going to be wildly confusing for AUX backlight.

BR,
Jani.

> +	if (ret < 0) {
> +		drm_err(display->drm,
> +			"[CONNECTOR:%d:%s] Failed to setup PWM backlight controls for eDP backlight: %d\n",
> +			connector->base.base.id, connector->base.name, ret);
> +		return ret;
>  	}
>  
>  	if (panel->backlight.edp.vesa.info.luminance_set) {

-- 
Jani Nikula, Intel