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We require n-1 mailboxes for proper semaphore synchronization. All semaphore synchronization code relies on proper values in these mailboxes. The fact that we failed to touch the vebox ring by itself was unlikely to be an issue since the HW should be initializing the values to 0. However the error framework for testing seqno wrap introduced by Mika, in addition to the hangcheck via seqno, and i915_error_first_batchbuffer() combined caused a nice explosion. The problem is caused by seqno wrap because the wrap condition is not properly setup. The wrap code attempts to set the sync mailboxes all to 0, and then set the current seqno to one less than 0. In all cases, the vebox mailbox wasn't properly being initialized. This caused a wrap to not occur. When hangcheck kicks in with the bogus seqno values, the rest just doesn't work. It makes me wonder if we shouldn't consider a dumber version of hangcheck... How we messed this up: VECS support was written before the aforementioned other features. Upon VECS being rebased, these facts were missed. Cc: Mika Kuoppala <mika.kuoppala@intel.com> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=65387 Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67198 Signed-off-by: Ben Widawsky <ben@bwidawsk.net> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> |
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