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Subject: Re: Safety of opening up /dev/dma_heap/* to physically present
 users (udev uaccess tag) ?
From: Nicolas Dufresne <nicolas.dufresne@collabora.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>, Simon Ser
	 <contact@emersion.fr>
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Date: Wed, 22 May 2024 09:02:21 -0400
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Le jeudi 16 mai 2024 =C3=A0 14:20 +0300, Laurent Pinchart a =C3=A9crit=C2=
=A0:
> On Thu, May 16, 2024 at 07:00:31AM +0000, Simon Ser wrote:
> > On Tuesday, May 14th, 2024 at 22:42, Laurent Pinchart wrote:
> >=20
> > > My experience on Arm platforms is that the KMS drivers offer allocati=
on
> > > for scanout buffers, not render buffers, and mostly using the dumb
> > > allocator API. If the KMS device can scan out YUV natively, YUV buffe=
r
> > > allocation should be supported. Am I missing something here ?
> >=20
> > Note that dumb buffers are only intended for simple software-rendering
> > use-cases. Anything more complicated (e.g. involving GPU rendering)
> > should use another mechanism.
>=20
> Sure. Even if dumb buffers may work for GPU rendering in some cases,
> there's no guarantee they will, so they shouldn't be used.
>=20
> My comment was related to scanout buffers, as I was puzzled by Nicolas
> mentioning how "KMS drivers only offer allocation for render buffers".
> On Arm platforms the render buffers are allocated on the GPU's DRM
> device as far as I understand, while the KMS drivers allocate scanout
> buffers using the dumb buffers API.
>=20

The message is getting distorted. I'm saying that not all supported formats=
 have
an allocation API in DRM/KMS drivers. Most YUV formats needed for media han=
dling
(GPU or scannout) are not supported.

Nicolas

p.s. I feel like commenters thinks its evident for userspace application to=
 know
if they are doing scanout or GPU ... while in reality, they offload their
allocated buffer to a compositor which will have to dynamically juggle betw=
een
these two with its own heuristic.