Re: [PATCH v2 06/10] dma-buf: heaps: Add support for Tegra VPR

[Maxime Ripard <mripard@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 2322 bytes --]

Hi,

On Thu, Jan 22, 2026 at 05:10:05PM +0100, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
> 
> NVIDIA Tegra SoCs commonly define a Video-Protection-Region, which is a
> region of memory dedicated to content-protected video decode and
> playback. This memory cannot be accessed by the CPU and only certain
> hardware devices have access to it.
> 
> Expose the VPR as a DMA heap so that applications and drivers can
> allocate buffers from this region for use-cases that require this kind
> of protected memory.
> 
> VPR has a few very critical peculiarities. First, it must be a single
> contiguous region of memory (there is a single pair of registers that
> set the base address and size of the region), which is configured by
> calling back into the secure monitor. The memory region also needs to
> quite large for some use-cases because it needs to fit multiple video
> frames (8K video should be supported), so VPR sizes of ~2 GiB are
> expected. However, some devices cannot afford to reserve this amount
> of memory for a particular use-case, and therefore the VPR must be
> resizable.
> 
> Unfortunately, resizing the VPR is slightly tricky because the GPU found
> on Tegra SoCs must be in reset during the VPR resize operation. This is
> currently implemented by freezing all userspace processes and calling
> invoking the GPU's freeze() implementation, resizing and the thawing the
> GPU and userspace processes. This is quite heavy-handed, so eventually
> it might be better to implement thawing/freezing in the GPU driver in
> such a way that they block accesses to the GPU so that the VPR resize
> operation can happen without suspending all userspace.
> 
> In order to balance the memory usage versus the amount of resizing that
> needs to happen, the VPR is divided into multiple chunks. Each chunk is
> implemented as a CMA area that is completely allocated on first use to
> guarantee the contiguity of the VPR. Once all buffers from a chunk have
> been freed, the CMA area is deallocated and the memory returned to the
> system.
> 
> Signed-off-by: Thierry Reding <treding@nvidia.com>

Aside from the discussion on CMA, it doesn't look like the heap defines
anywhere the attributes of the allocated buffers this heap provides.

Maxime

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 273 bytes --]