we see an issue where resets fails because the engine resumes from an incorrect RING_HEAD. Since the RING_HEAD doesn't point to the remaining requests to re-run, but may instead point into the uninitialised portion of the ring, the GPU may be then fed invalid instructions from a privileged context, oft pushing the GPU into an unrecoverable hang. If at first the write doesn't succeed, try, try again. v2: Avoid unnecessary timeout macro (Andi) v3: Correct comment format (Andi) v4: Make it generic for all platform as it won't impact (Chris) Link: https://gitlab.freedesktop.org/drm/intel/-/issues/5432 Testcase: igt/i915_selftest/hangcheck Signed-off-by: Chris Wilson <chris.p.wilson@xxxxxxxxxxxxxxx> Signed-off-by: Nitin Gote <nitin.r.gote@xxxxxxxxx> --- .../gpu/drm/i915/gt/intel_ring_submission.c | 31 ++++++++++++++++--- 1 file changed, 27 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/i915/gt/intel_ring_submission.c b/drivers/gpu/drm/i915/gt/intel_ring_submission.c index 72277bc8322e..b6b25fe22cb8 100644 --- a/drivers/gpu/drm/i915/gt/intel_ring_submission.c +++ b/drivers/gpu/drm/i915/gt/intel_ring_submission.c @@ -192,6 +192,7 @@ static bool stop_ring(struct intel_engine_cs *engine) static int xcs_resume(struct intel_engine_cs *engine) { struct intel_ring *ring = engine->legacy.ring; + ktime_t kt; ENGINE_TRACE(engine, "ring:{HEAD:%04x, TAIL:%04x}\n", ring->head, ring->tail); @@ -230,9 +231,27 @@ static int xcs_resume(struct intel_engine_cs *engine) set_pp_dir(engine); /* First wake the ring up to an empty/idle ring */ - ENGINE_WRITE_FW(engine, RING_HEAD, ring->head); + for ((kt) = ktime_get() + (2 * NSEC_PER_MSEC); + ktime_before(ktime_get(), (kt)); cpu_relax()) { + /* + * In case of resets fails because engine resumes from + * incorrect RING_HEAD and then GPU may be then fed + * to invalid instrcutions, which may lead to unrecoverable + * hang. So at first write doesn't succeed then try again. + */ + ENGINE_WRITE_FW(engine, RING_HEAD, ring->head); + if (ENGINE_READ_FW(engine, RING_HEAD) == ring->head) + break; + } + ENGINE_WRITE_FW(engine, RING_TAIL, ring->head); - ENGINE_POSTING_READ(engine, RING_TAIL); + if (ENGINE_READ_FW(engine, RING_HEAD) != ENGINE_READ_FW(engine, RING_TAIL)) { + ENGINE_TRACE(engine, "failed to reset empty ring: [%x, %x]: %x\n", + ENGINE_READ_FW(engine, RING_HEAD), + ENGINE_READ_FW(engine, RING_TAIL), + ring->head); + goto err; + } ENGINE_WRITE_FW(engine, RING_CTL, RING_CTL_SIZE(ring->size) | RING_VALID); @@ -241,12 +260,16 @@ static int xcs_resume(struct intel_engine_cs *engine) if (__intel_wait_for_register_fw(engine->uncore, RING_CTL(engine->mmio_base), RING_VALID, RING_VALID, - 5000, 0, NULL)) + 5000, 0, NULL)) { + ENGINE_TRACE(engine, "failed to restart\n"); goto err; + } - if (GRAPHICS_VER(engine->i915) > 2) + if (GRAPHICS_VER(engine->i915) > 2) { ENGINE_WRITE_FW(engine, RING_MI_MODE, _MASKED_BIT_DISABLE(STOP_RING)); + ENGINE_POSTING_READ(engine, RING_MI_MODE); + } /* Now awake, let it get started */ if (ring->tail != ring->head) { -- 2.25.1
