linux-kernel - Re: [PATCH v4] media: docs-rst: Document m2m stateless video decoder interface

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Date:   Wed, 17 Apr 2019 19:21:19 +0200
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Nicolas Dufresne <nicolas@...fresne.ca>,
        Alexandre Courbot <acourbot@...omium.org>,
        Tomasz Figa <tfiga@...omium.org>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Hans Verkuil <hverkuil@...all.nl>,
        Dafna Hirschfeld <dafna3@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] media: docs-rst: Document m2m stateless video
 decoder interface

Hi,

Le mercredi 17 avril 2019 à 12:17 -0400, Nicolas Dufresne a écrit :
> In general, we say stateless from a HW point of view. It simply means
> that the HW (the accelerator) can be multiplexed to process several
> independent streams. While with stateful firmware, you generally can't
> save the state, and ends up with a specific number of concurrent stream
> (scheduling happens in the firmware). There is exception to that of
> course, the newest Amlogic/Meson video decoder allow for saving the
> decoder state. The registers are undocumented, since they are filled by
> the HW parser, but it's separated in a way that we could multiplex.

That's a nice summary! I think it constitutes a good definition of what
we should call a stateless decoder. Perhaps we could write it down in
the spec somewhere?

> Of course we do have a state in our drivers. Each time you open an m2m
> device, you create an new instance which will keep track of done jobs,
> pending jobs, active format, allocated memory, etc.

Yes, definitely.

Cheers,

Paul