Re: [PATCH] drm/ttm: don't set page->mapping

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Am 05.11.20 um 10:11 schrieb Daniel Vetter:
On Thu, Nov 5, 2020 at 9:00 AM Christian König <christian.koenig@xxxxxxx> wrote:
Am 04.11.20 um 17:50 schrieb Daniel Vetter:
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@xxxxxxxxxx>
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@xxxxxxxxxx>
      Reviewed-by: Brian Paul <brianp@xxxxxxxxxx>

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.
NAK, we use this to determine if a pages belongs to the driver or not in
amdgpu for example.

Mostly used for debugging, but I would really like to keep that.
Can you pls point me at that code? A quick grep hasn't really found much at all.

See amdgpu_iomem_read() for an example:

                if (p->mapping != adev->mman.bdev.dev_mapping)
                        return -EPERM;

Christian.

-Daniel

Christian.

Cc: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
Cc: Brian Paul <brianp@xxxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Cc: Christian Koenig <christian.koenig@xxxxxxx>
Cc: Huang Rui <ray.huang@xxxxxxx>
---
   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 8861a74ac335..438ea43fd8c1 100644
--- a/drivers/gpu/drm/ttm/ttm_tt.c
+++ b/drivers/gpu/drm/ttm/ttm_tt.c
@@ -291,17 +291,6 @@ 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)
   {
@@ -320,7 +309,6 @@ 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);


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