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

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Message-ID: <526c1714-95f1-49ea-9bf1-a778e00ad6bf@ti.com>
Date: Thu, 24 Apr 2025 16:16:58 +0530
From: Jayesh Choudhary <j-choudhary@...com>
To: Doug Anderson <dianders@...omium.org>
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

Hello Doug,

On 17/04/25 02:40, Jayesh Choudhary wrote:
> Hello Doug,
> 
> On 13/04/25 07:22, Doug Anderson wrote:
>> 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 :-).
>>
> 
> Definitely.
> I will add more details for the commit message.
> 
> For more context here, I was working with cadence dsi driver for TI
> SoCs. So to be more accurate, this is required for CDNS_DSI
> 
> I observed other bridges like lt-9211, where I have seen such flags
> being set for dsi-controller by vendors.

Upon testing with modes other than video sync pulse mode,
I found that with the upcoming fixes in cdns-dsi-core driver made by
Tomi[0], this patch is no longer necessary.

[0]: 
https://lore.kernel.org/all/20250414-cdns-dsi-impro-v3-0-4e52551d4f07@ideasonboard.com/

I apologies for the noise in the mailing list.

Warm Regards,
Jayesh

> 
>>
>>> 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