linux-kernel - Re: [v2,2/3] drm/i915: Force DPCD backlight mode on X1 Extreme 2nd Gen 4K AMOLED panel

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Date:   Tue, 03 Mar 2020 14:50:02 -0500
From:   Adam Jackson <ajax@...hat.com>
To:     Lyude Paul <lyude@...hat.com>, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        Jani Nikula <jani.nikula@...el.com>,
        linux-kernel@...r.kernel.org, Maxime Ripard <mripard@...nel.org>,
        David Airlie <airlied@...ux.ie>
Subject: Re: [v2,2/3] drm/i915: Force DPCD backlight mode on X1 Extreme 2nd
 Gen 4K AMOLED panel

On Tue, 2020-02-11 at 13:33 -0500, Lyude Paul wrote:

> -	if (!intel_dp_aux_display_control_capable(intel_connector))
> +	/*
> +	 * There are a lot of machines that don't advertise the backlight
> +	 * control interface to use properly in their VBIOS, :\
> +	 */
> +	if (dev_priv->vbt.backlight.type !=
> +	    INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE &&
> +	    !drm_dp_has_quirk(&intel_dp->desc, intel_dp->edid_quirks,
> +			      DP_QUIRK_FORCE_DPCD_BACKLIGHT)) {
> +		DRM_DEV_INFO(dev->dev,
> +			     "Panel advertises DPCD backlight support, but "
> +			     "VBT disagrees. If your backlight controls "
> +			     "don't work try booting with "
> +			     "i915.enable_dpcd_backlight=1. If your machine "
> +			     "needs this, please file a _new_ bug report on "
> +			     "bugs.freedesktop.org against DRI -> "
> +			     "DRM/Intel\n");

Bugzilla's been put out of our misery, probably this should point to
gitlab instead.

- ajax