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Thu, 21 Aug 2025 03:17:17 -0700 (PDT) Date: Thu, 21 Aug 2025 13:17:15 +0300 From: Abel Vesa To: Val Packett Cc: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Suraj Kandpal , Arun R Murthy , ankit.k.nautiyal@intel.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] drm/dp: drm_edp_backlight_set_level: do not always send 3-byte commands Message-ID: References: <20250706204446.8918-1-val@packett.cool> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250706204446.8918-1-val@packett.cool> 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 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