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Thu, 16 Apr 2026 02:11:02 -0700 (PDT) Message-ID: Date: Thu, 16 Apr 2026 14:40:52 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/1] drm: bridge: ti-sn65dsi83: Fix DSI mode flags for stable LVDS output To: Luca Ceresoli , andrzej.hajda@intel.com, neil.armstrong@linaro.org, rfoss@kernel.org Cc: Laurent.pinchart@ideasonboard.com, jonas@kwiboo.se, jernej.skrabec@gmail.com, maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com, simona@ffwll.ch, marex@denx.de, valentin@compulab.co.il, philippe.schenker@toradex.com, alexander.stein@ew.tq-group.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20260412053811.662461-1-tessolveupstream@gmail.com> <20260412053811.662461-2-tessolveupstream@gmail.com> Content-Language: en-US From: tessolveupstream@gmail.com In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 15-04-2026 12:43, Luca Ceresoli wrote: > Hello Sudarshan, > > On Sun Apr 12, 2026 at 7:38 AM CEST, Sudarshan Shetty wrote: >> The current DSI mode configuration enables VIDEO_BURST and disables >> horizontal front porch (HFP) and back porch (HBP) transmission using >> MIPI_DSI_MODE_VIDEO_NO_HFP and MIPI_DSI_MODE_VIDEO_NO_HBP. >> >> However, the SN65DSI83/84 bridge relies on receiving full horizontal >> timing information over DSI in order to correctly reconstruct the LVDS >> output timings. When HFP and HBP are not transmitted, the bridge cannot >> recreate the required timing parameters, resulting in unstable or >> missing display output on some panels. >> >> Additionally, while burst mode is supported by the hardware, its use >> depends on continuous clock behavior from the DSI host. In practice, >> burst mode may introduce instability depending on the host controller >> implementation, as the DSI link may transition to low-power state >> between bursts. >> >> In testing, removing burst mode and ensuring full horizontal timing >> transmission results in stable LVDS output across affected panels. >> >> Update the DSI mode flags to: >> - Drop MIPI_DSI_MODE_VIDEO_BURST >> - Drop MIPI_DSI_MODE_VIDEO_NO_HFP >> - Drop MIPI_DSI_MODE_VIDEO_NO_HBP >> >> This aligns with common system configurations where non-burst mode is >> preferred and full timing information is transmitted over DSI. >> >> Signed-off-by: Sudarshan Shetty > > Thanks for having gone into the details and provide a good explanation for > the removal of these three flags. > > It would be still great to have authoritative info from TI, possibly as an > update to the documentation. > > I managed to test on a board with i.MX93, a TI SN65DSI84 and a 1920x1080p60 > panel, and: > > - no image shown with the current mainline driver > - it works by removing only MIPI_DSI_MODE_VIDEO_BURST (my current setup) > - it works with this patch applied > > Tested-by: Luca Ceresoli # imx93 1920x1080p60 > Thanks for testing the patch and for the Tested-by tag. I’ll reach out to TI for clarification on the DSI mode flag behavior and any documentation updates, and will share any feedback I receive, though I cannot guarantee a response. > Luca > > -- > Luca Ceresoli, Bootlin > Embedded Linux and Kernel engineering > https://bootlin.com