linux-kernel - Re: [PATCHv3 7/7] drm/msm/a6xx: Add support for using system cache(LLC)

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Message-ID: <ecfda7ca80f6d7b4ff3d89b8758f4dc9@codeaurora.org>
Date:   Fri, 03 Jul 2020 20:23:07 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Will Deacon <will@...nel.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Rob Clark <robdclark@...il.com>,
        iommu@...ts.linux-foundation.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Sean Paul <sean@...rly.run>,
        Sharat Masetty <smasetty@...eaurora.org>,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        freedreno@...ts.freedesktop.org, Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Emil Velikov <emil.velikov@...labora.com>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        "Kristian H . Kristensen" <hoegsberg@...gle.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCHv3 7/7] drm/msm/a6xx: Add support for using system
 cache(LLC)

Hi Will,

On 2020-07-03 19:07, Will Deacon wrote:
> On Mon, Jun 29, 2020 at 09:22:50PM +0530, Sai Prakash Ranjan wrote:
>> diff --git a/drivers/gpu/drm/msm/msm_iommu.c 
>> b/drivers/gpu/drm/msm/msm_iommu.c
>> index f455c597f76d..bd1d58229cc2 100644
>> --- a/drivers/gpu/drm/msm/msm_iommu.c
>> +++ b/drivers/gpu/drm/msm/msm_iommu.c
>> @@ -218,6 +218,9 @@ static int msm_iommu_map(struct msm_mmu *mmu, 
>> uint64_t iova,
>>  		iova |= GENMASK_ULL(63, 49);
>> 
>> 
>> +	if (mmu->features & MMU_FEATURE_USE_SYSTEM_CACHE)
>> +		prot |= IOMMU_SYS_CACHE_ONLY;
> 
> Given that I think this is the only user of IOMMU_SYS_CACHE_ONLY, then 
> it
> looks like it should actually be a property on the domain because we 
> never
> need to configure it on a per-mapping basis within a domain, and 
> therefore
> it shouldn't be exposed by the IOMMU API as a prot flag.
> 
> Do you agree?
> 

GPU being the only user is for now, but there are other clients which 
can use this.
Plus how do we set the memory attributes if we do not expose this as 
prot flag?

Thanks,
Sai

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