Re: [PATCH v2 13/18] media: ti: Add CSI2RX support for J721E

[Tomi Valkeinen]

Hi Pratyush,

On 26/05/2021 18:23, Pratyush Yadav wrote:
> TI's J721E uses the Cadence CSI2RX and DPHY peripherals to facilitate
> capture over a CSI-2 bus.
>
> The Cadence CSI2RX IP acts as a bridge between the TI specific parts and
> the CSI-2 protocol parts. TI then has a wrapper on top of this bridge
> called the SHIM layer. It takes in data from stream 0, repacks it, and
> sends it to memory over PSI-L DMA.
>
> This driver acts as the "front end" to V4L2 client applications. It
> implements the required ioctls and buffer operations, passes the
> necessary calls on to the bridge, programs the SHIM layer, and performs
> DMA via the dmaengine API to finally return the data to a buffer
> supplied by the application.
>
> Signed-off-by: Pratyush Yadav <p.yadav@xxxxxx>

I noticed that my test app didn't work at all with this, and I also 
wasn't able to use v4l2-ctl to set the format.

At least for my test app the problem was that this driver doesn't 
initialize the format at all. My app first calls VIDIOC_G_FMT with 
v4l2_format.type == V4L2_BUF_TYPE_VIDEO_CAPTURE, then after the call 
modifies the fields it wants to change and calls VIDIOC_S_FMT. This 
failed, as G_FMT returned uninitialized fmt, i.e. type was 0, which my 
app didn't set again.

I believe the driver should have an initial format, something that it 
will accept if an app calls G_FMT and then S_FMT.

 Tomi