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

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Message-ID: <7e4236cd59d1af009e23aabbd2c96735cbb379b3.camel@collabora.com>
Date: Mon, 17 Jun 2024 15:02:05 -0400
From: Nicolas Dufresne <nicolas.dufresne@...labora.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.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
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 Christian König <christian.koenig@....com>, Matthias
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 dri-devel@...ts.freedesktop.org,  linux-kernel@...r.kernel.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

Le mercredi 12 juin 2024 à 23:25 +0300, Laurent Pinchart a écrit :
> 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 ?

I believe so, yes.

> 
> > 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.
>