linux-kernel - Re: [PATCH] drm/dp: drm_edp_backlight_set_level: do not always send 3-byte commands

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aKbyKwf5XyUbVwdw@linaro.org>
Date: Thu, 21 Aug 2025 13:17:15 +0300
From: Abel Vesa <abel.vesa@...aro.org>
To: Val Packett <val@...kett.cool>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Suraj Kandpal <suraj.kandpal@...el.com>,
	Arun R Murthy <arun.r.murthy@...el.com>, ankit.k.nautiyal@...el.com,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/dp: drm_edp_backlight_set_level: do not always send
 3-byte commands

On 25-07-06 17:42:24, Val Packett wrote:
> At least some panels using the LSB register are not happy with the
> unconditional increase of the command buffer to 3 bytes.
> 
> With the BOE NE14QDM in my Dell Latitude 7455, the recent patches for
> luminance based brightness have introduced a regression: the brightness
> range stopped being contiguous and became nonsensical (it probably was
> interpreting the last 2 bytes of the buffer and not the first 2).
> 
> Change from using a fixed sizeof() to a length variable that's only
> set to 3 when luminance is used. Let's leave the default as 2 even for
> the single-byte version, since that's how it worked before.
> 
> Fixes: f2db78e37fe7 ("drm/dp: Modify drm_edp_backlight_set_level")
> Signed-off-by: Val Packett <val@...kett.cool>

Tested on Dell XPS 13 9345 which has LGD 134WT1 panel.
Without this, the panel doesn't come up at all on boot.

Tested-by: Abel Vesa <abel.vesa@...aro.org>