Hi, On Thu, Jan 22, 2026 at 05:10:05PM +0100, Thierry Reding wrote: > From: Thierry Reding <[email protected]> > > 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 <[email protected]>
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
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