linux-kernel - Re: [PATCH v2 4/4] drm/msm/a6xx: Use the DMA API for GMU memory objects

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Date:   Tue, 25 Feb 2020 15:54:19 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Jordan Crouse <jcrouse@...eaurora.org>
Cc:     linux-arm-msm@...r.kernel.org,
        Sharat Masetty <smasetty@...eaurora.org>,
        Sean Paul <sean@...rly.run>,
        Stephen Boyd <swboyd@...omium.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Douglas Anderson <dianders@...omium.org>,
        Rob Clark <robdclark@...il.com>,
        David Airlie <airlied@...ux.ie>,
        freedreno@...ts.freedesktop.org, Daniel Vetter <daniel@...ll.ch>,
        Todd Kjos <tkjos@...gle.com>
Subject: Re: [PATCH v2 4/4] drm/msm/a6xx: Use the DMA API for GMU memory objects

On Thu, Feb 20, 2020 at 10:27 AM Jordan Crouse <jcrouse@...eaurora.org> wrote:
>
> The GMU has very few memory allocations and uses a flat memory space so
> there is no good reason to go out of our way to bypass the DMA APIs which
> were basically designed for this exact scenario.
>
> v2: Pass force_dma false to of_dma_configure to require that the DMA
> region be set up and return error from of_dma_configure to fail probe.
>
> Signed-off-by: Jordan Crouse <jcrouse@...eaurora.org>
> ---
>
>  drivers/gpu/drm/msm/adreno/a6xx_gmu.c | 112 +++-------------------------------
>  drivers/gpu/drm/msm/adreno/a6xx_gmu.h |   5 +-
>  2 files changed, 11 insertions(+), 106 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> index 983afea..c36b38b 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
...
> -       count = bo->size >> PAGE_SHIFT;
> +       bo->virt = dma_alloc_attrs(gmu->dev, bo->size, &bo->iova, GFP_KERNEL,
> +               bo->attrs);
>
...
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.h b/drivers/gpu/drm/msm/adreno/a6xx_gmu.h
> index 2af91ed..31bd1987 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.h
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.h
> @@ -13,7 +13,7 @@ struct a6xx_gmu_bo {
>         void *virt;
>         size_t size;
>         u64 iova;
> -       struct page **pages;
> +       unsigned long attrs;
>  };

As a head up, Todd reported that this patch is causing build trouble
w/ arm32, as the iova needs to be a dma_attr_t.

I've got a patch for the android-mainline tree to fix this, but you
might want to spin a v3 to address this.
  https://android-review.googlesource.com/c/kernel/common/+/1243928

thanks
-john