Re: [PATCH v1 0/4] msm/gpu/a6xx: use the DMA-API for GMU memory allocations

John Stultz
2020-02-20T05:48:48Z

On Wed, Feb 19, 2020 at 1:33 PM Jordan Crouse <jcrouse@codeaurora.org> wrote:
>
> When CONFIG_INIT_ON_ALLOC_DEFAULT_ON the GMU memory allocator runs afoul of
> cache coherency issues because it is mapped as write-combine without clearing
> the cache after it was zeroed.
>
> Rather than duplicate the hacky workaround we use in the GEM allocator for the
> same reason it turns out that we don't need to have a bespoke memory allocator
> for the GMU anyway. It uses a flat, global address space and there are only
> two relatively minor allocations anyway. In short, this is essentially what the
> DMA API was created for so replace a bunch of memory management code with two
> calls to allocate and free DMA memory and we're fine.
>
> The only wrinkle is that the memory allocations need to be in a very specific
> location in the GMU virtual address space so in order to get the iova allocator
> to do the right thing we need to specify the dma-ranges property in the device
> tree for the GMU node. Since we've not yet converted the GMU bindings over to
> YAML two patches quickly turn into four but at the end of it we have at least
> one bindings file converted to YAML and 99 less lines of code to worry about.
>
> Jordan Crouse (4):
> dt-bindings: display: msm: Convert GMU bindings to YAML
> dt-bindings: display: msm: Add required dma-range property
> arm64: dts: sdm845: Set the virtual address range for GMU allocations
> drm/msm/a6xx: Use the DMA API for GMU memory objects

Awesome! Thanks so much for the quick turnaround on this! This set
resolves the crashes I was seeing with
CONFIG_INIT_ON_ALLOC_DEFAULT_ON.

Tested-by: John Stultz <john.stultz@linaro.org>

thanks again!
-john