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From:   Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Wed, 25 Nov 2020 17:28:32 +0100
Message-ID: <CAKMK7uGXfqaPUtnX=VgA3tFn3S+Gt9GV+kPguakZ6FF_n8LKuA@mail.gmail.com>
Subject: Re: [PATCH] drm/ttm: don't set page->mapping
To:     DRI Development <dri-devel@lists.freedesktop.org>
Cc:     Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
        Linux MM <linux-mm@kvack.org>, linux-xfs@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        Thomas Hellstrom <thellstrom@vmware.com>,
        Brian Paul <brianp@vmware.com>,
        Daniel Vetter <daniel.vetter@intel.com>,
        Christian Koenig <christian.koenig@amd.com>,
        Huang Rui <ray.huang@amd.com>
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On Wed, Nov 25, 2020 at 5:25 PM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>
> Random observation while trying to review Christian's patch series to
> stop looking at struct page for dma-buf imports.
>
> This was originally added in
>
> commit 58aa6622d32af7d2c08d45085f44c54554a16ed7
> Author: Thomas Hellstrom <thellstrom@vmware.com>
> Date:   Fri Jan 3 11:47:23 2014 +0100
>
>     drm/ttm: Correctly set page mapping and -index members
>
>     Needed for some vm operations; most notably unmap_mapping_range() with
>     even_cows = 0.
>
>     Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
>     Reviewed-by: Brian Paul <brianp@vmware.com>
>
> but we do not have a single caller of unmap_mapping_range with
> even_cows == 0. And all the gem drivers don't do this, so another
> small thing we could standardize between drm and ttm drivers.
>
> Plus I don't really see a need for unamp_mapping_range where we don't
> want to indiscriminately shoot down all ptes.
>
> Cc: Thomas Hellstrom <thellstrom@vmware.com>
> Cc: Brian Paul <brianp@vmware.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Christian Koenig <christian.koenig@amd.com>
> Cc: Huang Rui <ray.huang@amd.com>

Apologies again, this shouldn't have been included. But at least I
have an idea now why this patch somehow was included in the git
send-email. Lovely interface :-/
-Daniel

> ---
>  drivers/gpu/drm/ttm/ttm_tt.c | 12 ------------
>  1 file changed, 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
> index da9eeffe0c6d..5b2eb6d58bb7 100644
> --- a/drivers/gpu/drm/ttm/ttm_tt.c
> +++ b/drivers/gpu/drm/ttm/ttm_tt.c
> @@ -284,17 +284,6 @@ int ttm_tt_swapout(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
>         return ret;
>  }
>
> -static void ttm_tt_add_mapping(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
> -{
> -       pgoff_t i;
> -
> -       if (ttm->page_flags & TTM_PAGE_FLAG_SG)
> -               return;
> -
> -       for (i = 0; i < ttm->num_pages; ++i)
> -               ttm->pages[i]->mapping = bdev->dev_mapping;
> -}
> -
>  int ttm_tt_populate(struct ttm_bo_device *bdev,
>                     struct ttm_tt *ttm, struct ttm_operation_ctx *ctx)
>  {
> @@ -313,7 +302,6 @@ int ttm_tt_populate(struct ttm_bo_device *bdev,
>         if (ret)
>                 return ret;
>
> -       ttm_tt_add_mapping(bdev, ttm);
>         ttm->page_flags |= TTM_PAGE_FLAG_PRIV_POPULATED;
>         if (unlikely(ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)) {
>                 ret = ttm_tt_swapin(ttm);
> --
> 2.29.2
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch