Re: [RFC] Request API and V4L2 capabilities

From: Nicolas Dufresne <nicolas@ndufresne.ca>
To: Hans Verkuil <hverkuil@xs4all.nl>,
	Linux Media Mailing List <linux-media@vger.kernel.org>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Tomasz Figa <tfiga@chromium.org>,
	Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
	Maxime Ripard <maxime.ripard@bootlin.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>
Subject: Re: [RFC] Request API and V4L2 capabilities
Date: Thu, 23 Aug 2018 13:37:24 -0400	[thread overview]
Message-ID: <f4d1e18a6552446b092cffaa3028e0dfe5432b9a.camel@ndufresne.ca> (raw)
In-Reply-To: <b46ee744-4c00-7e73-1925-65f2122e30f0@xs4all.nl>

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Le jeudi 23 août 2018 à 16:31 +0200, Hans Verkuil a écrit :
> > I propose adding these capabilities:
> > 
> > #define V4L2_BUF_CAP_HAS_REQUESTS     0x00000001
> > #define V4L2_BUF_CAP_REQUIRES_REQUESTS        0x00000002
> > #define V4L2_BUF_CAP_HAS_MMAP         0x00000100
> > #define V4L2_BUF_CAP_HAS_USERPTR      0x00000200
> > #define V4L2_BUF_CAP_HAS_DMABUF               0x00000400
> 
> I substituted SUPPORTS for HAS and dropped the REQUIRES_REQUESTS capability.
> As Tomasz mentioned, technically (at least for stateless codecs) you could
> handle just one frame at a time without using requests. It's very inefficient,
> but it would work.

I thought the request was providing a data structure to refer back to
the frames, so each codec don't have to implement one. Do you mean that
the framework will implicitly request requests in that mode ? or simply
that there is no such helper ?

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