Re: [Intel-gfx] [RFC v4 08/11] drm/i915/dpcd_bl: Return early in vesa_calc_max_backlight if we can't read PWMGEN_BIT_COUNT

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Mon, Feb 08, 2021 at 06:38:58PM -0500, Lyude Paul wrote:
> If we can't read DP_EDP_PWMGEN_BIT_COUNT in
> intel_dp_aux_vesa_calc_max_backlight() but do have a valid PWM frequency
> defined in the VBT, we'll keep going in the function until we inevitably
> fail on reading DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN. There's not much point in
> doing this, so just return early.
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 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 611eb3a7cc08..a139f0e08839 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -449,11 +449,14 @@ static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connecto
>  	int freq, fxp, fxp_min, fxp_max, fxp_actual, f = 1;
>  	u8 pn, pn_min, pn_max;
>  
> -	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT, &pn) == 1) {
> -		pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> -		max_backlight = (1 << pn) - 1;
> +	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT, &pn) != 1) {
> +		drm_dbg_kms(&i915->drm, "Failed to read pwmgen bit count cap\n");
> +		return 0;
>  	}
>  
> +	pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> +	max_backlight = (1 << pn) - 1;
> +
>  	/* Find desired value of (F x P)
>  	 * Note that, if F x P is out of supported range, the maximum value or
>  	 * minimum value will applied automatically. So no need to check that.
> -- 
> 2.29.2
> 
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