[RFC PATCH v3 0/1] drm/amdgpu: MMIO TLB invalidation fallback when KIQ is wedged after S4 resume

[Denis Pisarev <pisarevden@gmail.com>]

Hi,

v3 addresses the two findings from the sashiko-bot review of v2.
Failure data and trigger isolation are unchanged (bugzilla 219492):
S4 resume on Cezanne (gmc_v9, GFXOFF) wedges KIQ TLB flushes at
80-140/hour for 9+ hours with sched.ready true throughout; holding
GFXOFF off across the S4 cycle produces zero errors.

1. [High] "VFs and interrupt contexts silently drop TLB flushes once
   the threshold is reached" - correct, and fixed. In v3 the latch
   only reroutes bare metal process context to MMIO. VFs and IRQ
   contexts keep submitting to KIQ exactly as before this patch, with
   per-failure logging, because they have no MMIO alternative; there
   is no longer any code path that drops a flush without attempting
   and logging.

2. [High] "KIQ and MMIO race on the same invalidation engine if KIQ
   recovers" - this remains the documented open question; no code
   change in v3. Our analysis: once latched, this path submits no new
   KIQ commands, so the exposure is limited to already-queued stale
   commands and the recovery transition window. The engine serializes
   requests internally, so the realistic worst case is a lost flush
   request caught by the existing ACK timeout ("Timeout waiting for VM
   flush ACK!"), not silent state corruption. If maintainers consider
   a fence necessary (or a dedicated invalidate engine for the MMIO
   path), guidance on the preferred mechanism would be welcome.

Full patch history: v1 (initial fallback+counter), v2 (GFXOFF hold,
per-instance counter, irqsave, VF/IRQ restrictions, MES error
propagation) - all from bot review; v3 (this one) fixes the VF/IRQ
drop regression the bot found in v2.

Also still open from the cover letters: the alternative direction of
fixing the S4 resume ordering itself (RLC/ME vs GFXOFF) instead of a
runtime fallback. Happy to run tracing on the affected hardware.

Patch 1/1 follows.

Denis Pisarev

Denis Pisarev (1):
  drm/amdgpu: fall back to MMIO TLB invalidation when KIQ is
    unresponsive

 drivers/gpu/drm/amd/amdgpu/amdgpu.h     |   2 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.h |   2 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c |  18 ++--
 drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h |   2 +-
 drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c   | 123 +++++++++++++++++++-----
 5 files changed, 114 insertions(+), 33 deletions(-)

-- 
2.55.0