Hi, Pierre-Eric

On Thu, 2025-11-13 at 17:05 +0100, Pierre-Eric Pelloux-Prayer wrote:

Until now ttm stored a single pipelined eviction fence which means drivers had to use a single entity for these evictions.

To lift this requirement, this commit allows up to 8 entities to be used.

Ideally a dma_resv object would have been used as a container of the eviction fences, but the locking rules makes it complex. dma_resv all have the same ww_class, which means "Attempting to lock more mutexes after ww_acquire_done." is an error.

One alternative considered was to introduced a 2nd ww_class for specific resv to hold a single "transient" lock (= the resv lock would only be held for a short period, without taking any other locks).

Wouldn't it be possible to use lockdep_set_class_and_name() to modify the resv lock class for these particular resv objects after they are allocated? Reusing the resv code certainly sounds attractive.

Thanks, Thomas