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

[Laurent Pinchart]

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