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

[Nicolas Dufresne]

Hi,

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 ?

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

Nicolas

> 
> > 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.
>