Re: [PATCH 2/2] drm: bridge: tc358767: give VSDELAY some positive value

[Marek Vasut <marex@denx.de>]

On 6/2/23 21:15, Lucas Stach wrote:
> From: David Jander <david@protonic.nl>
> 
> The documentation is not clear about how this delay works.
> Empirical tests have shown that with a VSDELAY of 0, the first
> scanline is not properly formatted in the output stream when
> DSI->DP mode is used. The calculation spreadsheets from Toshiba
> seem to always make this value equal to the HFP + 10 for DSI->DP
> use-case. For DSI->DPI this value should be > 2 and for DPI->DP
> it seems to always be 0x64.
> 
> Signed-off-by: David Jander <david@protonic.nl>
> Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> ---
>   drivers/gpu/drm/bridge/tc358767.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
> index 46916ae30f8f..9f2c67b4a488 100644
> --- a/drivers/gpu/drm/bridge/tc358767.c
> +++ b/drivers/gpu/drm/bridge/tc358767.c
> @@ -817,7 +817,7 @@ static int tc_set_common_video_mode(struct tc_data *tc,
>   	 * sync signals
>   	 */
>   	ret = regmap_write(tc->regmap, VPCTRL0,
> -			   FIELD_PREP(VSDELAY, 0) |
> +			   FIELD_PREP(VSDELAY, right_margin + 10) |
>   			   OPXLFMT_RGB888 | FRMSYNC_DISABLED | MSF_DISABLED);
>   	if (ret)
>   		return ret;

Aren't you running into a problem due to VS timing misconfiguration on 
the scanout engine or DSI serializer side ? The VSDELAY seems to 
increase the length of VSYNC active . Which DSI bus mode do you use, 
sync events/pulses/burst ?