linux-kernel - Re: [PATCH 07/13] drm/msm: Use sychronized interface of the IOMMU-API

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Date:   Sat, 19 Aug 2017 11:39:35 -0400
From:   Rob Clark <robdclark@...il.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        Joerg Roedel <jroedel@...e.de>,
        David Airlie <airlied@...ux.ie>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>
Subject: Re: [PATCH 07/13] drm/msm: Use sychronized interface of the IOMMU-API

On Thu, Aug 17, 2017 at 8:56 AM, Joerg Roedel <joro@...tes.org> wrote:
> From: Joerg Roedel <jroedel@...e.de>
>
> The map and unmap functions of the IOMMU-API changed their
> semantics: They do no longer guarantee that the hardware
> TLBs are synchronized with the page-table updates they made.
>
> To make conversion easier, new synchronized functions have
> been introduced which give these guarantees again until the
> code is converted to use the new TLB-flush interface of the
> IOMMU-API, which allows certain optimizations.
>
> But for now, just convert this code to use the synchronized
> functions so that it will behave as before.


I like the idea of decoupling tlb inv with map (well that doesn't
really effect any recent hw) and unmap (which does need tlb flush)..
and for a gpu driver it should be pretty easy to back up unmaps.

I did slightly prefer adding a new iommu_{map,unmap}_async() rather
than changing semantics of existing API, but either way:

Acked-by: Rob Clark <robdclark@...il.com>

> Cc: Rob Clark <robdclark@...il.com>
> Cc: David Airlie <airlied@...ux.ie>
> Cc: linux-arm-msm@...r.kernel.org
> Cc: dri-devel@...ts.freedesktop.org
> Cc: freedreno@...ts.freedesktop.org
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
>  drivers/gpu/drm/msm/msm_iommu.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c
> index b23d336..b3525b7 100644
> --- a/drivers/gpu/drm/msm/msm_iommu.c
> +++ b/drivers/gpu/drm/msm/msm_iommu.c
> @@ -64,7 +64,8 @@ static int msm_iommu_map(struct msm_mmu *mmu, uint64_t iova,
>         size_t ret;
>
>  //     pm_runtime_get_sync(mmu->dev);
> -       ret = iommu_map_sg(iommu->domain, iova, sgt->sgl, sgt->nents, prot);
> +       ret = iommu_map_sg_sync(iommu->domain, iova, sgt->sgl,
> +                               sgt->nents, prot);
>  //     pm_runtime_put_sync(mmu->dev);
>         WARN_ON(ret < 0);
>
> @@ -77,7 +78,7 @@ static int msm_iommu_unmap(struct msm_mmu *mmu, uint64_t iova,
>         struct msm_iommu *iommu = to_msm_iommu(mmu);
>
>         pm_runtime_get_sync(mmu->dev);
> -       iommu_unmap(iommu->domain, iova, len);
> +       iommu_unmap_sync(iommu->domain, iova, len);
>         pm_runtime_put_sync(mmu->dev);
>
>         return 0;
> --
> 2.7.4
>