Re: [PATCH v2 0/2] drm: bridge: ti-sn65dsi83: Improve dual-link LVDS support

["Luca Ceresoli" <luca.ceresoli@bootlin.com>]

Hello Sudarshan,

and thanks Marek for copying me, I hadn't noticed this series.

On Thu Mar 12, 2026 at 1:35 PM CET, tessolveupstream wrote:

[...]

>> +CC Luca
>>
>> 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/

> During our earlier debugging, we went through several trial-and-error
> iterations and also received support from TI. According to TI, when
> operating in dual-link mode the horizontal timing parameters must be
> divided by two before being written to the device. Without this
> adjustment, the panel either does not light up or shows corrupted output.
>
> TI also shared a set of recommended register settings for dual-link mode,
> which were derived using the TI DSI-Tuner tool. These settings helped us
> get the panel working on our hardware during testing.
> For reference, the register configuration suggested by TI is as follows:
>
> 	regmap_write(ctx->regmap, REG_RC_LVDS_PLL, 0x05);
> 	regmap_write(ctx->regmap, REG_RC_PLL_EN, 0x00);
> 	regmap_write(ctx->regmap, REG_DSI_CLK, 0x53);
> 	regmap_write(ctx->regmap, REG_LVDS_FMT, 0x6f);
> 	regmap_write(ctx->regmap, REG_LVDS_VCOM, 0x00);
> 	regmap_write(ctx->regmap,
> 		     REG_VID_CHA_VERTICAL_DISPLAY_SIZE_LOW, 0x00);
> 	regmap_write(ctx->regmap,
> 		     REG_VID_CHA_VERTICAL_DISPLAY_SIZE_HIGH, 0x00);
> 	regmap_write(ctx->regmap,
> 		     REG_VID_CHA_HSYNC_PULSE_WIDTH_LOW, 0x10);
> 	regmap_write(ctx->regmap,
> 		     REG_VID_CHA_HORIZONTAL_BACK_PORCH, 0x28);
> 	regmap_write(ctx->regmap,
> 		     REG_VID_CHA_VERTICAL_BACK_PORCH, 0x00);
> 	regmap_write(ctx->regmap,
> 		     REG_VID_CHA_HORIZONTAL_FRONT_PORCH, 0x00);
> 	regmap_write(ctx->regmap,
> 		     REG_VID_CHA_VERTICAL_FRONT_PORCH, 0x00);
>
> If it would help, we can test any proposed changes on our hardware.

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.

Hope this helps,
Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com