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Message-ID: <33d38919f3f94b6e1848aaee20cf52ac9c1df606.camel@collabora.com>
Subject: Re: [PATCH v6,04/24] v4l: add documentation for restricted memory
 flag
From: Nicolas Dufresne <nicolas.dufresne@collabora.com>
To: Tomasz Figa <tfiga@chromium.org>, Laurent Pinchart
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Cc: Yunfei Dong <yunfei.dong@mediatek.com>, Jeffrey Kardatzke
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Date: Wed, 12 Jun 2024 15:43:58 -0400
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Hi,

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 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 ?
>=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 restricted
> (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 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 lat=
est):

- The driver needs to communicate through the OPTEE rather then SCP and som=
e
communication are needed just to figure-out things like supported profile/l=
evel
resolutions etc.
- The driver needs to allocate auxiliary buffers in secure heap too, alloca=
tion
at runtime are not the best

Note that the discussion around this flag already took place in the very fi=
rst
iteration of the serie, it was originally using a CID and that was a propos=
ed
replacement from Hans.

regards,
Nicolas