Re: [Freedreno] [PATCH 0/3] iommu/drm/msm: Allow non-coherent masters to use system cache
From: Will Deacon <will@kernel.org>
Date: 2021-08-10 09:16:32
Also in:
dri-devel, linux-arm-msm, linux-iommu, lkml
On Mon, Aug 09, 2021 at 11:17:40PM +0530, Sai Prakash Ranjan wrote:
On 2021-08-09 23:10, Will Deacon wrote:quoted
On Mon, Aug 09, 2021 at 10:18:21AM -0700, Rob Clark wrote:quoted
On Mon, Aug 9, 2021 at 10:05 AM Will Deacon [off-list ref] wrote:quoted
On Mon, Aug 09, 2021 at 09:57:08AM -0700, Rob Clark wrote:quoted
But I suppose we could call it instead IOMMU_QCOM_LLC or something like that to make it more clear that it is not necessarily something that would work with a different outer level cache implementation?... or we could just deal with the problem so that other people can reuse the code. I haven't really understood the reluctance to solve this properly. Am I missing some reason this isn't solvable?Oh, was there another way to solve it (other than foregoing setting INC_OCACHE in the pgtables)? Maybe I misunderstood, is there a corresponding setting on the MMU pgtables side of things?Right -- we just need to program the CPU's MMU with the matching memory attributes! It's a bit more fiddly if you're just using ioremap_wc() though, as it's usually the DMA API which handles the attributes under the hood. Anyway, sorry, I should've said that explicitly earlier on. We've done this sort of thing in the Android tree so I assumed Sai knew what needed to be done and then I didn't think to explain to you :(Right I was aware of that but even in the android tree there is no user :)
I'm assuming there are vendor modules using it there, otherwise we wouldn't have been asked to put it in. Since you work at Qualcomm, maybe you could talk to your colleagues (Isaac and Patrick) directly?
I think we can't have a new memory type without any user right in upstream like android tree?
Correct. But I don't think we should be adding IOMMU_* anything upstream if we don't have a user. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel