linux-kernel - Re: [PATCH v3 4/5] drm/dp, drm/i915: Add support for VESA backlights using PWM for brightness control

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Date:   Tue, 12 Oct 2021 13:45:04 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Lyude Paul <lyude@...hat.com>
Cc:     Intel Graphics <intel-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "open list:DRM DRIVER FOR NVIDIA GEFORCE/QUADRO GPUS" 
        <nouveau@...ts.freedesktop.org>,
        Rajeev Nandan <rajeevny@...eaurora.org>,
        Satadru Pramanik <satadru@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Sean Paul <seanpaul@...omium.org>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 4/5] drm/dp, drm/i915: Add support for VESA backlights
 using PWM for brightness control

Hi,

On Tue, Oct 5, 2021 at 7:41 PM Lyude Paul <lyude@...hat.com> wrote:
>
> @@ -1859,8 +1859,7 @@ drm_dp_sink_can_do_video_without_timing_msa(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
>  static inline bool
>  drm_edp_backlight_supported(const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE])
>  {
> -       return (edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
> -               (edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP);
> +       return !!(edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP);
>  }

nit: I don't believe that the "!!" is needed in the above. C should
automatically handle this since the return type of the function is
"bool".

I've reviewed the generic (non-intel) code and it looks like a
reasonable approach to me.

Reviewed-by: Douglas Anderson <dianders@...omium.org>