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Message-ID: <03aca2439ac31ec01b24233384cc8c8d5179df02.camel@collabora.com>
Subject: Re: [PATCH v6,04/24] v4l: add documentation for restricted memory
 flag
From: Nicolas Dufresne <nicolas.dufresne@collabora.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Tomasz Figa <tfiga@chromium.org>, Yunfei Dong
 <yunfei.dong@mediatek.com>,  Jeffrey Kardatzke <jkardatzke@google.com>,
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Date: Wed, 12 Jun 2024 16:58:58 -0400
In-Reply-To: <20240612202507.GT28989@pendragon.ideasonboard.com>
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Hi,

Le mercredi 12 juin 2024 =C3=A0 23:25 +0300, Laurent Pinchart a =C3=A9crit=
=C2=A0:
> On Wed, Jun 12, 2024 at 03:43:58PM -0400, Nicolas Dufresne wrote:
> > Le mercredi 12 juin 2024 =C3=A0 13:37 +0900, Tomasz Figa a =C3=A9crit=
=C2=A0:
> > > > Why is this flag needed ? Given that the usage model requires the V=
4L2
> > > > 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 ?
> > >=20
> > > Given that the flag is specified at REQBUF / CREATE_BUFS time, it's
> > > actually useful to tell the driver the queue is operating in restrict=
ed
> > > (aka secure) mode.
> > >=20
> > > 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 pa=
in.
> > > So I'd say that the design being proposed here makes things simpler a=
nd
> > > more clear, even if it doesn't add any extra functionality.
> >=20
> > There is few more reasons I notice in previous series (haven't read the=
 latest):
> >=20
> > - The driver needs to communicate through the OPTEE rather then SCP and=
 some
> > communication are needed just to figure-out things like supported profi=
le/level
> > resolutions etc.
> > - The driver needs to allocate auxiliary buffers in secure heap too, al=
location
> > at runtime are not the best
>=20
> Will the same driver support both modes on the same system ?

Yes, as per this implementation, it seems you can flip from one mode to ano=
ther
even on the same instance.

Nicolas

>=20
> > Note that the discussion around this flag already took place in the ver=
y first
> > iteration of the serie, it was originally using a CID and that was a pr=
oposed
> > replacement from Hans.
>=20