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Currently we face a severe problem on Braswell that manifests as invalid ppGTT accesses. The code tries to maintain the PDP (page directory pointers) inside the context in two ways, direct write into the context and a pipelined LRI update. The direct write into the context is fundamentally racy as it is unserialised with any access (read or write) the GPU is doing. By asserting that Braswell is not used with vGPU (currently an unsupported platform) we can eliminate the dangerous direct write into the context image and solely use the pipelined update. However, the LRI of the PDP fouls up the GPU, causing it to freeze and take out the machine with "forcewake ack timeouts". This seems possible to workaround by preventing the GPU from sleeping (via means of disabling the power-state management interface, i.e. forcing each ring to remain awake) around the update. Equally, it seems an EMIT_INVALIDATE before the LRI is sufficient to prevent the forcewake errors. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108656 References: https://bugs.freedesktop.org/show_bug.cgi?id=108714 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20181207090213.14352-3-chris@chris-wilson.co.uk |
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