linux-kernel - Re: [PATCH v2 7/8] drm/msm/a6xx: Support split pagetables

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Message-ID: <CAF6AEGuchn7fa+8j45sCH7Sd2_dz5WokeeinR8RYr8xvY4Uq+g@mail.gmail.com>
Date:   Mon, 9 Dec 2019 12:17:53 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Jordan Crouse <jcrouse@...eaurora.org>
Cc:     "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Sean Paul <sean@...rly.run>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Mamta Shukla <mamtashukla555@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH v2 7/8] drm/msm/a6xx: Support split pagetables

On Fri, Nov 22, 2019 at 3:32 PM Jordan Crouse <jcrouse@...eaurora.org> wrote:
>
> Attempt to enable split pagetables if the arm-smmu driver supports it.
> This will move the default address space from the default region to
> the address range assigned to TTBR1. The behavior should be transparent
> to the driver for now but it gets the default buffers out of the way
> when we want to start swapping TTBR0 for context-specific pagetables.
>
> Signed-off-by: Jordan Crouse <jcrouse@...eaurora.org>
> ---
>
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 46 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 45 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index 5dc0b2c..96b3b28 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -811,6 +811,50 @@ static unsigned long a6xx_gpu_busy(struct msm_gpu *gpu)
>         return (unsigned long)busy_time;
>  }
>
> +static struct msm_gem_address_space *
> +a6xx_create_address_space(struct msm_gpu *gpu, struct platform_device *pdev)
> +{
> +       struct iommu_domain *iommu = iommu_domain_alloc(&platform_bus_type);
> +       struct msm_gem_address_space *aspace;
> +       struct msm_mmu *mmu;
> +       u64 start, size;
> +       u32 val = 1;
> +       int ret;
> +
> +       if (!iommu)
> +               return ERR_PTR(-ENOMEM);
> +
> +       /* Try to request split pagetables */
> +       iommu_domain_set_attr(iommu, DOMAIN_ATTR_SPLIT_TABLES, &val);
> +
> +       mmu = msm_iommu_new(&pdev->dev, iommu);
> +       if (IS_ERR(mmu)) {
> +               iommu_domain_free(iommu);
> +               return ERR_CAST(mmu);
> +       }
> +
> +       /* Check to see if split pagetables were successful */
> +       ret = iommu_domain_get_attr(iommu, DOMAIN_ATTR_SPLIT_TABLES, &val);

I assume the split between this and iommu_domain_set_attr() is because
attach needs to happen in between?  At any rate, if it needs to be
like this, maybe a comment is in order.  As it is it looks like
something future-self would "cleanup"..

BR,
-R

> +       if (!ret && val) {
> +               /*
> +                * The aperture start will be at the beginning of the TTBR1
> +                * space so use that as a base
> +                */
> +               start = iommu->geometry.aperture_start;
> +               size = 0xffffffff;
> +       } else {
> +               /* Otherwise use the legacy 32 bit region */
> +               start = SZ_16M;
> +               size = 0xffffffff - SZ_16M;
> +       }
> +
> +       aspace = msm_gem_address_space_create(mmu, "gpu", start, size);
> +       if (IS_ERR(aspace))
> +               iommu_domain_free(iommu);
> +
> +       return aspace;
> +}
> +
>  static const struct adreno_gpu_funcs funcs = {
>         .base = {
>                 .get_param = adreno_get_param,
> @@ -832,7 +876,7 @@ static const struct adreno_gpu_funcs funcs = {
>  #if defined(CONFIG_DRM_MSM_GPU_STATE)
>                 .gpu_state_get = a6xx_gpu_state_get,
>                 .gpu_state_put = a6xx_gpu_state_put,
> -               .create_address_space = adreno_iommu_create_address_space,
> +               .create_address_space = a6xx_create_address_space,
>  #endif
>         },
>         .get_timestamp = a6xx_get_timestamp,
> --
> 2.7.4
>