[PATCH v3 1/2] drm/i915: Fix negative value passed as remaining time

[Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>]

Commit b97060a99b01 ("drm/i915/guc: Update intel_gt_wait_for_idle to work
with GuC") extended the API of intel_gt_retire_requests_timeout() with an
extra argument 'remaining_timeout', intended for passing back unconsumed
portion of requested timeout when 0 (success) is returned.  However, when
request retirement happens to succeed despite an error returned by a call
to dma_fence_wait_timeout(), that error code (a negative value) is passed
back instead of remaining time.  If we then pass that negative value
forward as requested timeout to intel_uc_wait_for_idle(), an explicit BUG
will be triggered.

If request retirement succeeds but an error code is passed back via
remaininig_timeout, we may have no clue on how much of the initial timeout
might have been left for spending it on waiting for GuC to become idle.
OTOH, since all pending requests have been successfully retired, that
error code has been already ignored by intel_gt_retire_requests_timeout(),
then we shouldn't fail.

Assume no more time has been left on error and pass 0 timeout value to
intel_uc_wait_for_idle() to give it a chance to return success if GuC is
already idle.

v3: Don't fail on any error passed back via remaining_timeout.

v2: Fix the issue on the caller side, not the provider.

Fixes: b97060a99b01 ("drm/i915/guc: Update intel_gt_wait_for_idle to work with GuC")
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Cc: stable@vger.kernel.org # v5.15+
---
 drivers/gpu/drm/i915/gt/intel_gt.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c b/drivers/gpu/drm/i915/gt/intel_gt.c
index b5ad9caa55372..7ef0edb2e37cd 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt.c
@@ -677,8 +677,13 @@ int intel_gt_wait_for_idle(struct intel_gt *gt, long timeout)
 			return -EINTR;
 	}
 
-	return timeout ? timeout : intel_uc_wait_for_idle(&gt->uc,
-							  remaining_timeout);
+	if (timeout)
+		return timeout;
+
+	if (remaining_timeout < 0)
+		remaining_timeout = 0;
+
+	return intel_uc_wait_for_idle(&gt->uc, remaining_timeout);
 }
 
 int intel_gt_init(struct intel_gt *gt)
-- 
2.25.1