linux-kernel - Re: [PATCH] drm/bridge: ti-sn65dsi86: Add necessary DSI flags

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Message-ID: <CAD=FV=Vkj_YnmYnDF3K+eYZ5M4fFPgGdmryHS8ijZOLZWbt6ZA@mail.gmail.com>
Date: Sat, 12 Apr 2025 18:52:03 -0700
From: Doug Anderson <dianders@...omium.org>
To: Jayesh Choudhary <j-choudhary@...com>
Cc: andrzej.hajda@...el.com, neil.armstrong@...aro.org, rfoss@...nel.org, 
	Laurent.pinchart@...asonboard.com, dri-devel@...ts.freedesktop.org, 
	jonas@...boo.se, jernej.skrabec@...il.com, maarten.lankhorst@...ux.intel.com, 
	mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com, simona@...ll.ch, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: ti-sn65dsi86: Add necessary DSI flags

Hi,

On Fri, Apr 11, 2025 at 2:23 AM Jayesh Choudhary <j-choudhary@...com> wrote:
>
> Enable NO_EOT and SYNC flags for DSI to use VIDEO_SYNC_PULSE_MODE
> with EOT disabled.

Any chance you could add some details to this commit message? Your
subject says that these flags are "necessary", but people have been
using this driver successfully for many years now. Why did these flags
suddenly become necessary and why were things working before?

I'm not saying that we shouldn't use these flags, just trying to
understand. I actually don't know a ton about these details in MIPI,
so it would help me :-).


> Signed-off-by: Jayesh Choudhary <j-choudhary@...com>
> ---
>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index f72675766e01..8e9a7eb927da 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -707,7 +707,8 @@ static int ti_sn_attach_host(struct auxiliary_device *adev, struct ti_sn65dsi86
>         /* TODO: setting to 4 MIPI lanes always for now */
>         dsi->lanes = 4;
>         dsi->format = MIPI_DSI_FMT_RGB888;
> -       dsi->mode_flags = MIPI_DSI_MODE_VIDEO;
> +       dsi->mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_NO_EOT_PACKET |
> +                         MIPI_DSI_MODE_VIDEO_SYNC_PULSE;

FWIW, I can confirm that on my board the screen still seems to light
up after this change. ...so I'd be OK w/

Tested-by: Douglas Anderson <dianders@...omium.org>

...before giving a Reviewed-by I'd want a description that helps me
understand it better.

-Doug