linux-kernel - Re: [Freedreno] [PATCH 0/3] iommu/drm/msm: Allow non-coherent masters to use system cache

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Date:   Mon, 2 Aug 2021 08:08:07 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Will Deacon <will@...nel.org>
Cc:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Georgi Djakov <djakov@...nel.org>,
        "Isaac J. Manjarres" <isaacm@...eaurora.org>,
        David Airlie <airlied@...ux.ie>,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sean Paul <sean@...rly.run>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Kristian H Kristensen <hoegsberg@...gle.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Daniel Vetter <daniel@...ll.ch>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Robin Murphy <robin.murphy@....com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Freedreno] [PATCH 0/3] iommu/drm/msm: Allow non-coherent masters
 to use system cache

On Mon, Aug 2, 2021 at 3:55 AM Will Deacon <will@...nel.org> wrote:
>
> On Thu, Jul 29, 2021 at 10:08:22AM +0530, Sai Prakash Ranjan wrote:
> > On 2021-07-28 19:30, Georgi Djakov wrote:
> > > On Mon, Jan 11, 2021 at 07:45:02PM +0530, Sai Prakash Ranjan wrote:
> > > > commit ecd7274fb4cd ("iommu: Remove unused IOMMU_SYS_CACHE_ONLY flag")
> > > > removed unused IOMMU_SYS_CACHE_ONLY prot flag and along with it went
> > > > the memory type setting required for the non-coherent masters to use
> > > > system cache. Now that system cache support for GPU is added, we will
> > > > need to set the right PTE attribute for GPU buffers to be sys cached.
> > > > Without this, the system cache lines are not allocated for GPU.
> > > >
> > > > So the patches in this series introduces a new prot flag IOMMU_LLC,
> > > > renames IO_PGTABLE_QUIRK_ARM_OUTER_WBWA to IO_PGTABLE_QUIRK_PTW_LLC
> > > > and makes GPU the user of this protection flag.
> > >
> > > Thank you for the patchset! Are you planning to refresh it, as it does
> > > not apply anymore?
> > >
> >
> > I was waiting on Will's reply [1]. If there are no changes needed, then
> > I can repost the patch.
>
> I still think you need to handle the mismatched alias, no? You're adding
> a new memory type to the SMMU which doesn't exist on the CPU side. That
> can't be right.
>

Just curious, and maybe this is a dumb question, but what is your
concern about mismatched aliases?  I mean the cache hierarchy on the
GPU device side (anything beyond the LLC) is pretty different and
doesn't really care about the smmu pgtable attributes..

BR,
-R