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Shirish S authored
In amdgpu_dm_commit_tail(), wait until flip_done() is signaled before we signal hw_done(). [Why] This is to temporarily address a paging error that occurs when a nonblocking commit contends with another commit, particularly in a mirrored display configuration where at least 2 CRTCs are updated. The error occurs in drm_atomic_helper_wait_for_flip_done(), when we attempt to access the contents of new_crtc_state->commit. Here's the sequence for a mirrored 2 display setup (irrelevant steps left out for clarity): **THREAD 1** | **THREAD 2** | Initialize atomic state for flip | | Queue worker | ... | Do work for flip | | Signal hw_done() on CRTC 1 | Signal hw_done() on CRTC 2 | | Wait for flip_done() on CRTC 1 <---- **PREEMPTED BY THREAD 1** Initialize atomic state for cursor | update (1) | | Do cursor update work on both CRTCs | | Clear atomic state (2) | **DONE** | ... | | Wait for flip_done() on CRTC 2 | *ERROR* | The issue starts with (1). When the atomic state is initialized, the current CRTC states are duplicated to be the new_crtc_states, and referenced to be the old_crtc_states. (The new_crtc_states are to be filled with update data.) Some things to note: * Due to the mirrored configuration, the cursor updates on both CRTCs. * At this point, the pflip IRQ has already been handled, and flip_done signaled on all CRTCs. The cursor commit can therefore continue. * The old_crtc_states used by the cursor update are the **same states** as the new_crtc_states used by the flip worker. At (2), the old_crtc_state is freed (*), and the cursor commit completes. We then context switch back to the flip worker, where we attempt to access the new_crtc_state->commit object. This is problematic, as this state has already been freed. (*) Technically, 'state->crtcs[i].state' is freed, which was made to reference old_crtc_state in drm_atomic_helper_swap_state() [How] By moving hw_done() after wait_for_flip_done(), we're guaranteed that the new_crtc_state (from the flip worker's perspective) still exists. This is because any other commit will be blocked, waiting for the hw_done() signal. Note that both the i915 and imx drivers have this sequence flipped already, masking this problem. Signed-off-by:
Shirish S <shirish.s@amd.com> Signed-off-by:
Leo Li <sunpeng.li@amd.com> Reviewed-by:
Harry Wentland <harry.wentland@amd.com> Signed-off-by:
Alex Deucher <alexander.deucher@amd.com>
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