Re: [PATCH v2 0/2] drm/xe: flush engine buffers before signalling user fence on all engines

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Tue, 2024-06-04 at 11:38 +0200, Andrzej Hajda wrote:
> According to the discussion result on my previous patch I have
> prepared
> new patchset, which reverts previous patch and adds barrier before
> user fence signalling.
> Remarks:
> - I was not able to test it yet, hopefully CI will do it and me also
> after fixing LNL issue,
> - I am not sure about MI_FLUSH_DW flags, bspec says:
>   "After this command is completed with a Store DWord enabled, CPU
> access to graphics memory will be coherent"
>   Shouldn't we use "Store DWord" then?

It's not impossible that "store dword" needs to be enabled to act as a
write barrier. but it also says "The parser pauses on an internal flush
until all drawing engines have completed any pending operations."

If it turns out a store dword is indeed needed as a post sync
operation, we could perhaps use the "store dword" functionality of this
command to store the user-fence value and replace the posted write.

/Thomas

> 
> [1]:
> https://lore.kernel.org/intel-xe/Zl5DcuZeZiFgxVdJ@DUT025-TGLU.fm.intel.com/T/#m0b4420045908bac70426728d460108c0b2b65dca
> 
> Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
> ---
> - Link to v1:
> https://lore.kernel.org/r/20240603-fix_user_fence_posted-v1-1-61c76ef69cea@intel.com
> 
> ---
> Andrzej Hajda (2):
>       Revert "drm/xe: flush gtt before signalling user fence on all
> engines"
>       drm/xe: flush engine buffers before signalling user fence on
> all engines
> 
>  drivers/gpu/drm/xe/xe_ring_ops.c | 26 ++++++++++++++++++++------
>  1 file changed, 20 insertions(+), 6 deletions(-)
> ---
> base-commit: fe3d637a9c72b22297da0c731fa5e217bd182d2d
> change-id: 20240603-fix_user_fence_posted-ca56c79c0662
> 
> Best regards,