Message-ID: <8b8e603f-5d04-44ce-91ab-85df8fe0ae94@ideasonboard.com>
Date: Wed, 21 Jan 2026 09:38:29 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Jai Luthra <jai.luthra@...asonboard.com>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>, y-abhilashchandra@...com,
 devarsht@...com, s-jain1@...com, vigneshr@...com, mchehab@...nel.org,
 robh@...nel.org, krzk+dt@...nel.org, p.zabel@...gutronix.de,
 conor+dt@...nel.org, hverkuil-cisco@...all.nl,
 changhuang.liang@...rfivetech.com, jack.zhu@...rfivetech.com,
 sjoerd@...labora.com, dan.carpenter@...aro.org, hverkuil+cisco@...nel.org,
 linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
 devicetree@...r.kernel.org, jai.luthra@...ux.dev, mripard@...nel.org,
 Rishikesh Donadkar <r-donadkar@...com>
Subject: Re: [PATCH v9 06/19] media: ti: j721e-csi2rx: add a subdev for the
 core device

Hi,

On 21/01/2026 01:25, Laurent Pinchart wrote:
> On Thu, Jan 15, 2026 at 02:56:21PM +0200, Tomi Valkeinen wrote:
>> On 15/01/2026 08:36, Jai Luthra wrote:
>>> Quoting Tomi Valkeinen (2026-01-14 20:51:49)
>>>> On 30/12/2025 10:32, Rishikesh Donadkar wrote:
>>>>> From: Jai Luthra <j-luthra@...com>
>>>>>
>>>>> With single stream capture, it was simpler to use the video device as
>>>>> the media entity representing the main TI CSI2RX device. Now with multi
>>>>> stream capture coming into the picture, the model has shifted to each
>>>>> video device having a link to the main device's subdev. The routing
>>>>> would then be set on this subdev.
>>>>>
>>>>> Add this subdev, link each context to this subdev's entity and link the
>>>>> subdev's entity to the source. Also add an array of media pads. It will
>>>>> have one sink pad and source pads equal to the number of contexts.
>>>>>
>>>>> Support the new enable_stream()/disable_stream() APIs in the subdev
>>>>> instead of s_stream() hook.
>>>>>
>>>>> Reviewed-by: Yemike Abhilash Chandra <y-abhilashchandra@...com>
>>>>> Co-developed-by: Pratyush Yadav <p.yadav@...com>
>>>>> Signed-off-by: Pratyush Yadav <p.yadav@...com>
>>>>> Signed-off-by: Jai Luthra <j-luthra@...com>
>>>>> Signed-off-by: Rishikesh Donadkar <r-donadkar@...com>
>>>>> ---
>>>
>>> [...]
>>>
>>>>> @@ -981,48 +1138,52 @@ static int ti_csi2rx_link_validate(struct media_link *link)
>>>>>       struct ti_csi2rx_ctx *ctx = container_of(vdev, struct ti_csi2rx_ctx, vdev);
>>>>>       struct ti_csi2rx_dev *csi = ctx->csi;
>>>>>       struct v4l2_pix_format *csi_fmt = &ctx->v_fmt.fmt.pix;
>>>>> -     struct v4l2_subdev_format source_fmt = {
>>>>> -             .which  = V4L2_SUBDEV_FORMAT_ACTIVE,
>>>>> -             .pad    = link->source->index,
>>>>> -     };
>>>>> +     struct v4l2_mbus_framefmt *format;
>>>>> +     struct v4l2_subdev_state *state;
>>>>>       const struct ti_csi2rx_fmt *ti_fmt;
>>>>> -     int ret;
>>>>>  
>>>>> -     ret = v4l2_subdev_call_state_active(csi->source, pad,
>>>>> -                                         get_fmt, &source_fmt);
>>>>> -     if (ret)
>>>>> -             return ret;
>>>>> +     state = v4l2_subdev_lock_and_get_active_state(&csi->subdev);
>>>>> +     format = v4l2_subdev_state_get_format(state, link->source->index, 0);
>>>>> +     v4l2_subdev_unlock_state(state);
>>>>>  
>>>>> -     if (source_fmt.format.width != csi_fmt->width) {
>>>>> +     if (!format) {
>>>>> +             dev_dbg(csi->dev,
>>>>> +                     "Skipping validation as no format present on \"%s\":%u:0\n",
>>>>> +                     link->source->entity->name, link->source->index);
>>>>> +             return 0;
>>>>
>>>> Isn't this an error?
>>>
>>> Well, the j7 shim subdev introduced here has immutable and active links to
>>> all the video nodes, for each DMA channel (taken from DT), many of which
>>> may be unused for certain setups, and thus there might not be any valid
>>> format on the subdev source pad corresponding to an unused video node.
>>>
>>> Jacopo had a similar comment on v2, see this discussion (grep for Mali):
>>> https://lore.kernel.org/linux-media/4mnlnsj4co3agvln4qsasmgvgwiyoo7yu2h5wyh4rmzzafhm5u@avhnbw7iknms/
>>>
>>> I know other drivers use a different approach with mutable links, so it
>>> would be good if you/Laurent/Sakari can give your opinions on if only one
>>> of these two approaches should be taken for multi-stream pipelines.
>>
>> I see.
>>
>> Well, I don't have a definite answer. With some thinking both options
>> make certain sense. It makes sense to keep the links immutable and
>> always enabled, as there's no configuration that can be done. On the
>> other hand, it makes sense to require the unused links to be disabled,
>> as, well, they are not used.
> 
> I'm not familiar with the implications this would have on this driver,
> but generally speaking, if a stream is added to the media pipeline by
> the pipeline build algorithm, then it is expected that applications
> would have configured it correctly. Streams that are not used are
> expected to be disabled if they would otherwise be added to the
> pipeline.
> 

I think the thing here is that the driver creates immutable
always-enabled media links between the videodevs and the first subdev.
Then, say, if only one stream is being used, only one of those links is
actually used, and for every other link the above check fails as there's
no stream, so no format.

In TI CAL driver the links were mutable, and unused links had to be
disabled. There it made sense as the links had to be configurable (there
were two PHYs). Here, there's no configuration needed, so immutable
links make sense, but then they're enabled even when actually not used.

 Tomi

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