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

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Message-ID: <20200703133732.GD18953@willie-the-truck>
Date:   Fri, 3 Jul 2020 14:37:33 +0100
From:   Will Deacon <will@...nel.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.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)

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?

Will