Re: [PATCH] drm/i915/backlight: Fix VESA backlight possible check condition

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Apr 01, 2026 at 09:13:32AM +0530, Suraj Kandpal wrote:
> VESA backlight is possible through AUX only when
> BACKLIGHT_AUX_ENABLE_CAPABLE is true or when we use BL_ENABLE bit
> to enable backlight. Since that is not implemented we need to make
> sure we do not try to manipulate backlight when
> BACKLIGHT_AUX_ENABLE_CAPABLE is not set.
> Also fix return value when condition is not fulfilled.
> 
> Fixes: 40d2f5820951 ("drm/i915/backlight: Remove try_vesa_interface")
> Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>

Appears to work.
Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

I filed a bug with a dump of all platform information, mainly for posterity:
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/15907

> ---
>  drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 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 d0c76632a946..138d5b5e5482 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -615,8 +615,9 @@ check_if_vesa_backlight_possible(struct intel_dp *intel_dp)
>  	int ret;
>  	u8 bit_min, bit_max;
>  
> -	if (!(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP))
> -		return true;
> +	if (!(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP &&
> +	      intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP))
> +		return false;
>  
>  	ret = drm_dp_dpcd_read_byte(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &bit_min);
>  	if (ret < 0)
> -- 
> 2.34.1

-- 
Ville Syrjälä
Intel