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It is a bad idea for i915_add_request() to fail. The work will already have been send to the ring and will be processed, but there will not be any tracking or management of that work. The only way the add request call can fail is if it can't write its epilogue commands to the ring (cache flushing, seqno updates, interrupt signalling). The reasons for that are mostly down to running out of ring buffer space and the problems associated with trying to get some more. This patch prevents that situation from happening in the first place. When a request is created, it marks sufficient space as reserved for the epilogue commands. Thus guaranteeing that by the time the epilogue is written, there will be plenty of space for it. Note that a ring_begin() call is required to actually reserve the space (and do any potential waiting). However, that is not currently done at request creation time. This is because the ring_begin() code can allocate a request. Hence calling begin() from the request allocation code would lead to infinite recursion! Later patches in this series remove the need for begin() to do the allocate. At that point, it becomes safe for the allocate to call begin() and really reserve the space. Until then, there is a potential for insufficient space to be available at the point of calling i915_add_request(). However, that would only be in the case where the request was created and immediately submitted without ever calling ring_begin() and adding any work to that request. Which should never happen. And even if it does, and if that request happens to fall down the tiny window of opportunity for failing due to being out of ring space then does it really matter because the request wasn't doing anything in the first place? v2: Updated the 'reserved space too small' warning to include the offending sizes. Added a 'cancel' operation to clean up when a request is abandoned. Added re-initialisation of tracking state after a buffer wrap to keep the sanity checks accurate. v3: Incremented the reserved size to accommodate Ironlake (after finally managing to run on an ILK system). Also fixed missing wrap code in LRC mode. v4: Added extra comment and removed duplicate WARN (feedback from Tomas). For: VIZ-5115 CC: Tomas Elf <tomas.elf@intel.com> Signed-off-by: John Harrison <John.C.Harrison@Intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> |
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| ipu-v3 | ||
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| Makefile | ||