Hi, On Mon, Jul 21, 2025 at 01:17:29PM +0200, Maxime Ripard wrote: > Here's another attempt at supporting user-space allocations from a > specific carved-out reserved memory region. > > The initial problem we were discussing was that I'm currently working on > a platform which has a memory layout with ECC enabled. However, enabling > the ECC has a number of drawbacks on that platform: lower performance, > increased memory usage, etc. So for things like framebuffers, the > trade-off isn't great and thus there's a memory region with ECC disabled > to allocate from for such use cases. > > After a suggestion from John, I chose to first start using heap > allocations flags to allow for userspace to ask for a particular ECC > setup. This is then backed by a new heap type that runs from reserved > memory chunks flagged as such, and the existing DT properties to specify > the ECC properties. > > After further discussion, it was considered that flags were not the > right solution, and relying on the names of the heaps would be enough to > let userspace know the kind of buffer it deals with. > > Thus, even though the uAPI part of it had been dropped in this second > version, we still needed a driver to create heaps out of carved-out memory > regions. In addition to the original usecase, a similar driver can be > found in BSPs from most vendors, so I believe it would be a useful > addition to the kernel. > > Some extra discussion with Rob Herring [1] came to the conclusion that > some specific compatible for this is not great either, and as such an > new driver probably isn't called for either. > > Some other discussions we had with John [2] also dropped some hints that > multiple CMA heaps might be a good idea, and some vendors seem to do > that too. > > So here's another attempt that doesn't affect the device tree at all and > will just create a heap for every CMA reserved memory region. > > It also falls nicely into the current plan we have to support cgroups in > DRM/KMS and v4l2, which is an additional benefit. > > Let me know what you think, > Maxime
Any chance we can get this merged? Maxime
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