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

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Message-ID: <5b6953c5afdf566c248a2da59f91d9de@codeaurora.org>
Date:   Tue, 10 Aug 2021 15:24:41 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Will Deacon <will@...nel.org>
Cc:     Rob Clark <robdclark@...il.com>,
        "Isaac J. Manjarres" <isaacm@...eaurora.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        David Airlie <airlied@...ux.ie>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "list@....net:IOMMU DRIVERS , Joerg Roedel <joro@...tes.org>," 
        <iommu@...ts.linux-foundation.org>,
        Kristian H Kristensen <hoegsberg@...gle.com>,
        Daniel Vetter <daniel@...ll.ch>, Sean Paul <sean@...rly.run>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [Freedreno] [PATCH 0/3] iommu/drm/msm: Allow non-coherent masters
 to use system cache

On 2021-08-10 14:46, Will Deacon wrote:
> On Mon, Aug 09, 2021 at 11:17:40PM +0530, Sai Prakash Ranjan wrote:
>> On 2021-08-09 23:10, Will Deacon wrote:
>> > On Mon, Aug 09, 2021 at 10:18:21AM -0700, Rob Clark wrote:
>> > > On Mon, Aug 9, 2021 at 10:05 AM Will Deacon <will@...nel.org> wrote:
>> > > > On Mon, Aug 09, 2021 at 09:57:08AM -0700, Rob Clark wrote:
>> > > > > 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?
> 

Right I will check with them regarding the vendor modules in android.

>> 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.
> 

Agreed, once we have the fix for GPU crash I can continue further on 
using
this properly.

Thanks,
Sai

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