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Thu, 19 Mar 2026 02:55:02 -0700 (PDT) Message-ID: Date: Thu, 19 Mar 2026 15:25:22 +0530 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/2] drm: bridge: ti-sn65dsi83: Improve dual-link LVDS support To: Luca Ceresoli , Marek Vasut , 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, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, valentin@compulab.co.il, philippe.schenker@toradex.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org References: <20260312043743.261475-1-tessolveupstream@gmail.com> <9f694b2d-44bc-46ad-8aa3-b464c2f0da13@nabladev.com> <176ed865-11a6-42de-89e0-06951b59a430@gmail.com> <49b79a0d-844b-4fee-bccb-706187ed76d1@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 18-03-2026 14:21, Luca Ceresoli wrote: > Hello Sudarshan, > > On Wed Mar 18, 2026 at 6:45 AM CET, tessolveupstream wrote: >>>>> You might want to look at recently posted: >>>>> >>>>> [PATCH 2/3] drm/bridge: ti-sn65dsi83: halve horizontal syncs for dual LVDS output >>>> >>>> Thanks for pointing this out. >>>> I tried applying the patch “[PATCH 2/3] drm/bridge: ti-sn65dsi83: halve horizontal syncs for dual LVDS output” on top of the current tree and >>>> removed the changes that I had previously added in the driver. >>>> However, with this patch applied, I am currently seeing only the backlight turning on and no image on the LVDS panel. >>>> For reference, the LVDS panel used on our platform is G133HAN01.1 and the >>>> DSI-to-dual-link LVDS bridge is SN65DSI84ZXHR. >>> >>> Thanks for having tried. >>> >>> Can you please test with both the fixes in the series applied + the test >>> pattern feature and report the results you get with and without test >>> pattern enabled? >>> >>> The patches to apply are: >>> >>> - https://lore.kernel.org/all/20260226-ti-sn65dsi83-dual-lvds-fixes-and-test-pattern-v1-1-2e15f5a9a6a0@bootlin.com/ >>> - https://lore.kernel.org/all/20260226-ti-sn65dsi83-dual-lvds-fixes-and-test-pattern-v1-2-2e15f5a9a6a0@bootlin.com/ >>> - https://lore.kernel.org/lkml/20260309-ti-sn65dsi83-dual-lvds-fixes-and-test-pattern-v2-1-e6aaa7e1d181@bootlin.com/ >>> >> >> Thanks for the suggestions. >> >> I tested the three patches together as mentioned, but the LVDS panel >> still only shows the backlight and no image. I also tried removing the >> test-pattern patch and retesting with only the remaining two fixes, but >> the result remained the same — only the backlight turns on and no image >> is displayed. > > Sure, the test pattern patch does not change anything, unless you enable > the test pattern. > >>> The first thing I suggest doing on your side is testing with the 3 patches >>> mentioned above. >>> >>> If you display works, good! Let us know (you can also add your Tested-by / >>> Reviewed-by tags to the test_pattern patch too if applicable). >>> >>> If it doesn't work, compare the individual register values to find the >>> differences, try to figure out why the working setting works and how to >>> apply that change to the driver in away that keeps other boards >>> working. You're welcome to come back here to discuss it in case you can't >>> find out on your own. >>> >> >> I tested the three patches as suggested, but the panel still shows only the >> backlight with no visible image. I’m unsure how to translate the working >> register values into a generic fix based on display timings. Any guidance >> on the right direction would be helpful. > > What you should do is: > > 1. with your patches, and while the display is enabled (and working) do > > cat /sys/kernel/debug/regmap/4-002c/registers >regs.working > > 2. remove your patches, add the 3 I mentioned, and while the display is > enabled (but only backlight is working) do > > cat /sys/kernel/debug/regmap/4-002c/registers >regs.broken > > Then compare regs.working and regs.broken. Which registers differ? Can you > give a reason for the differences? > > You can come back with these values here so we may discuss them. > I followed your suggestion and captured the register dumps in both cases. ~# cat regs.working 00: 35 01: 38 02: 49 03: 53 04: 44 05: 20 06: 20 07: 20 08: 01 09: 01 0a: 85 0b: 28 0d: 01 10: 26 11: 00 12: 53 18: 6f 19: 00 1a: 03 1b: 00 20: 80 21: 07 24: 00 25: 00 28: 21 29: 00 2c: 10 2d: 00 30: 0e 31: 00 34: 28 36: 00 38: 00 3a: 00 3c: 00 e0: 00 e1: 00 e5: 00 ~# cat regs.broken 00: 35 01: 38 02: 49 03: 53 04: 44 05: 20 06: 20 07: 20 08: 01 09: 01 0a: 85 0b: 28 0d: 01 10: 26 11: 00 12: 55 18: 0f 19: 05 1a: 03 1b: 00 20: 80 21: 07 24: 38 25: 04 28: 21 29: 00 2c: 15 2d: 00 30: 0e 31: 00 34: 2c 36: 0e 38: 1d 3a: 08 3c: 00 e0: 00 e1: 00 e5: 00 In the working case, several of the timing registers remain at 0, while in the broken case they are programmed with non-zero values. > Luca > > -- > Luca Ceresoli, Bootlin > Embedded Linux and Kernel engineering > https://bootlin.com