linux-kernel - Re: [PATCH v6,04/24] v4l: add documentation for restricted memory flag

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Message-ID: <20240612202507.GT28989@pendragon.ideasonboard.com>
Date: Wed, 12 Jun 2024 23:25:07 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Nicolas Dufresne <nicolas.dufresne@...labora.com>
Cc: Tomasz Figa <tfiga@...omium.org>,
	Yunfei Dong <yunfei.dong@...iatek.com>,
	Jeffrey Kardatzke <jkardatzke@...gle.com>,
	Nícolas F . R . A . Prado <nfraprado@...labora.com>,
	Nathan Hebert <nhebert@...omium.org>,
	Hans Verkuil <hverkuil-cisco@...all.nl>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Benjamin Gaignard <benjamin.gaignard@...labora.com>,
	Sebastian Fricke <sebastian.fricke@...labora.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Chen-Yu Tsai <wenst@...omium.org>, Yong Wu <yong.wu@...iatek.com>,
	Hsin-Yi Wang <hsinyi@...omium.org>,
	Fritz Koenig <frkoenig@...omium.org>,
	Daniel Vetter <daniel@...ll.ch>, Steve Cho <stevecho@...omium.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Brian Starkey <Brian.Starkey@....com>,
	John Stultz <jstultz@...gle.com>,
	"T . J . Mercier" <tjmercier@...gle.com>,
	Christian König <christian.koenig@....com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
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	Project_Global_Chrome_Upstream_Group@...iatek.com
Subject: Re: [PATCH v6,04/24] v4l: add documentation for restricted memory
 flag

On Wed, Jun 12, 2024 at 03:43:58PM -0400, Nicolas Dufresne wrote:
> Le mercredi 12 juin 2024 à 13:37 +0900, Tomasz Figa a écrit :
> > > Why is this flag needed ? Given that the usage model requires the V4L2
> > > device to be a dma buf importer, why would userspace set the
> > > V4L2_BUF_CAP_SUPPORTS_RESTRICTED_MEM flag and pass a non-restricted
> > > buffer to the device ?
> > 
> > Given that the flag is specified at REQBUF / CREATE_BUFS time, it's
> > actually useful to tell the driver the queue is operating in restricted
> > (aka secure) mode.
> > 
> > I suppose we could handle that at the time of a first QBUF, but that
> > would make the driver initialization and validation quite a bit of pain.
> > So I'd say that the design being proposed here makes things simpler and
> > more clear, even if it doesn't add any extra functionality.
> 
> There is few more reasons I notice in previous series (haven't read the latest):
> 
> - The driver needs to communicate through the OPTEE rather then SCP and some
> communication are needed just to figure-out things like supported profile/level
> resolutions etc.
> - The driver needs to allocate auxiliary buffers in secure heap too, allocation
> at runtime are not the best

Will the same driver support both modes on the same system ?

> Note that the discussion around this flag already took place in the very first
> iteration of the serie, it was originally using a CID and that was a proposed
> replacement from Hans.

-- 
Regards,

Laurent Pinchart