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

From: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
To: Nicolas Dufresne <nicolas@ndufresne.ca>,
	Alexandre Courbot <acourbot@chromium.org>,
	Tomasz Figa <tfiga@chromium.org>,
	Maxime Ripard <maxime.ripard@bootlin.com>,
	Hans Verkuil <hverkuil@xs4all.nl>,
	Dafna Hirschfeld <dafna3@gmail.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	linux-media@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] media: docs-rst: Document m2m stateless video decoder interface
Date: Wed, 17 Apr 2019 19:21:19 +0200	[thread overview]
Message-ID: <943166ee9799daf50615b1148f3f855aa90e9c84.camel@bootlin.com> (raw)
In-Reply-To: <ec607c4917cd205f69de9a19c13a2109ff602477.camel@ndufresne.ca>

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