Re: [PATCH v2 2/2] media: imx: vdic: Introduce mem2mem VDI deinterlacer driver

On Do, 2024-10-03 at 16:57 +0200, Marek Vasut wrote:

On 9/26/24 1:16 PM, Philipp Zabel wrote:

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On Mi, 2024-09-25 at 22:45 +0200, Marek Vasut wrote:
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The driver is not taking ownership of prev_buf, only curr_buf is guaranteed to
exist until v4l2_m2m_job_finish() is called. Usespace could streamoff, allocate
new buffers, and then an old freed buffer may endup being used.

So, what should I do about this ? Is there some way to ref the buffer to
keep it around ?

Have a look how other deinterlacers with temporal filtering do it.
sunxi/sun8i-di or ti/vpe look like candidates.

I don't see exactly what those drivers are doing differently to protect 
the prev buffer during deinterlacing . Can you be more specific ?

In the EOF interrupt you are calling v4l2_m2m_buf_done() on src_buf,
which should be the same as ctx->curr_buf in the previous device_run.
Instead, you could release ctx->prev_buf and then store src_buf into
ctx->prev_buf. Storing curr_buf on the ctx doesn't seem to be necessary
at all. The mentioned deinterlacer drivers do something similar [1][2].

[1] https://elixir.bootlin.com/linux/master/source/drivers/media/platform/sunxi/sun8i-di/sun8i-di.c#L236
[2] https://elixir.bootlin.com/linux/master/source/drivers/media/platform/ti/vpe/vpe.c#L1481

regards
Philipp