Re: [PATCH v2] drm/i915/backlight: Fix VESA backlight possible check condition

["Nautiyal, Ankit K" <ankit.k.nautiyal@intel.com>]

On 4/7/2026 8:37 AM, Suraj Kandpal wrote:
> VESA backlight enable is possible when
> BACKLIGHT_AUX_ENABLE_CAPABLE is true via AUX command or when
> BACKLIGHT_PIN_ENABLE_CAPABLE is true via eDP connector pin.
> Similarly, backlight brightness adjustment can be
> done via AUX-based control or PWM pin-based control.
> It means there can be three configurations:
> 1) Full AUX-based: Enable and adjustment both via AUX. We currently
>     support this (apart from the AUX luminance-based backlight control).
> 2) Hybrid: Enable via the BL_ENABLE pin, adjustment via either AUX or
>     PWM.
> 3) Fully PWM pin-based: Enable via the BL_ENABLE pin, adjustment via
>     PWM.
> Since that only 1 is supported as of now 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.
>
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/15907
> Fixes: 0fb03890d182 ("drm/i915/backlight: Check if VESA backlight is possible")
> Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
> Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>


> ---
>   drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 9 +++++++--
>   1 file changed, 7 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..a8d56ebf06a2 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 +615,13 @@ 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;
> +	/*
> +	 * Since we only support Fully AUX Based VESA Backlight interface make sure
> +	 * backlight enable is possible via AUX along with backlight adjustment
> +	 */
> +	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP &&
> +	      intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP))
> +		return false;
>   
>   	ret = drm_dp_dpcd_read_byte(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &bit_min);
>   	if (ret < 0)