Re: [PATCH] drm/ttm: fix incorrect TT->SYSTEM move handling

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Am 16.09.20 um 21:27 schrieb Dave Airlie:
> On Thu, 17 Sep 2020 at 00:24, Christian König
> <ckoenig.leichtzumerken@gmail.com> wrote:
>> When we move from the SYSTEM domain to the TT domain
>> we still need to potentially change the caching state.
>>
>> This is most likely the source of a bunch of problems with
>> AGP and USWC together with hibernation and swap.
> I'm going to need more commentary, because I've been staring at this
> code a lot in the past few days and I'm although I dislike this path,
> I'm not sure what this brings.
>
> The current code flow to me is for SYSTEM->TT domain
>
> ttm_tt_create
> ttm_tt_set_placement_caching (new placement)
> ttm_tt_bind (can cause populate)
> move_notify
> replace pointers
> evicted = false
> return
>
> The new flow looks like
> ttm_tt_create
> ttm_tt_set_placement_caching (new placement)
> ttm_tt_bind (can cause populate)
> move_notify
> (via ttm_bo_move_ttm)
> ttm_tt_set_placement_caching (new placement)
> ttm_tt_bind
> replace pointers
> (back to main code)
> evicted = false
> return
>
> Is the second set placement caching doing something different here? or
> is there something that happens in move notify that we need to set
> things afterwards?

Oh, I was blind. Haven't seen the call to ttm_tt_set_placement_caching() 
directly before this one.

So forget this one, need to keep searching why hibernation doesn't work :(

Christian.

>
> Dave.
>
>> Signed-off-by: Christian König <christian.koenig@amd.com>
>> CC: stable@vger.kernel.org
>> ---
>>   drivers/gpu/drm/ttm/ttm_bo.c | 8 --------
>>   1 file changed, 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
>> index ffbdc20d8e8d..5f7efc90970e 100644
>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
>> @@ -264,13 +264,6 @@ static int ttm_bo_handle_move_mem(struct ttm_buffer_object *bo,
>>                          if (ret)
>>                                  goto out_err;
>>                  }
>> -
>> -               if (bo->mem.mem_type == TTM_PL_SYSTEM) {
>> -                       if (bdev->driver->move_notify)
>> -                               bdev->driver->move_notify(bo, evict, mem);
>> -                       bo->mem = *mem;
>> -                       goto moved;
>> -               }
>>          }
>>
>>          if (bdev->driver->move_notify)
>> @@ -293,7 +286,6 @@ static int ttm_bo_handle_move_mem(struct ttm_buffer_object *bo,
>>                  goto out_err;
>>          }
>>
>> -moved:
>>          bo->evicted = false;
>>
>>          ctx->bytes_moved += bo->num_pages << PAGE_SHIFT;
>> --
>> 2.17.1
>>

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