From d8f505311717cfc2033c44a8b26ba96c66187303 Mon Sep 17 00:00:00 2001 From: Mika Kuoppala Date: Wed, 5 Dec 2018 15:46:12 +0200 Subject: [PATCH] drm/i915/icl: Forcibly evict stale csb entries Gen11 fails to deliver wrt global observation point on tail/entry updates and we sometimes see old entry. Use clflush to forcibly evict our possibly stale copy of the cacheline in hopes that we get fresh one from gpu. Obviously there is something amiss in the coherency protocol so this can be consired as a workaround until real cause is found. The working hardware will do the evict without our cue anyways, so the cost in there should be ameliorated by that fact. v2: for next pass, s/flush/evict, add reset (Chris) References: https://bugzilla.freedesktop.org/show_bug.cgi?id=108315 Cc: Chris Wilson Signed-off-by: Mika Kuoppala Reviewed-by: Chris Wilson Link: https://patchwork.freedesktop.org/patch/msgid/20181205134612.24822-1-mika.kuoppala@linux.intel.com --- drivers/gpu/drm/i915/intel_lrc.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c index 27d3a780611a..3a47a4732fae 100644 --- a/drivers/gpu/drm/i915/intel_lrc.c +++ b/drivers/gpu/drm/i915/intel_lrc.c @@ -770,6 +770,13 @@ execlists_cancel_port_requests(struct intel_engine_execlists * const execlists) execlists_clear_all_active(execlists); } +static inline void +invalidate_csb_entries(const u32 *first, const u32 *last) +{ + clflush((void *)first); + clflush((void *)last); +} + static void reset_csb_pointers(struct intel_engine_execlists *execlists) { const unsigned int reset_value = GEN8_CSB_ENTRIES - 1; @@ -785,6 +792,9 @@ static void reset_csb_pointers(struct intel_engine_execlists *execlists) */ execlists->csb_head = reset_value; WRITE_ONCE(*execlists->csb_write, reset_value); + + invalidate_csb_entries(&execlists->csb_status[0], + &execlists->csb_status[GEN8_CSB_ENTRIES - 1]); } static void nop_submission_tasklet(unsigned long data) @@ -1020,6 +1030,19 @@ static void process_csb(struct intel_engine_cs *engine) } while (head != tail); execlists->csb_head = head; + + /* + * Gen11 has proven to fail wrt global observation point between + * entry and tail update, failing on the ordering and thus + * we see an old entry in the context status buffer. + * + * Forcibly evict out entries for the next gpu csb update, + * to increase the odds that we get a fresh entries with non + * working hardware. The cost for doing so comes out mostly with + * the wash as hardware, working or not, will need to do the + * invalidation before. + */ + invalidate_csb_entries(&buf[0], &buf[GEN8_CSB_ENTRIES - 1]); } static void __execlists_submission_tasklet(struct intel_engine_cs *const engine) -- 2.11.0