[Intel-gfx] [PATCH v2 1/2] drm/i915: Fix negative value passed as remaining time

[Janusz Krzysztofik]

On Friday, 18 November 2022 11:42:21 CET Janusz Krzysztofik wrote:
> 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 other than -ETIME is
> passed back via remaininig_timeout, we have no clue on how much of
> the initial timeout might have been left for spending it on waiting for
> GuC to become idle.  Then, we have no choice other than fail in that case
> -- do it.  

Looking at this again, I think we should ignore those errors, like they have 
been already ignored by intel_gt_retire_requests_timeout() returning 0, and 
call intel_uc_wait_for_idle() with 0 timeout.

I'll submit new version if you agree.

Thanks,
Janusz

> However, if -ETIME is returned via remaining_timeout then we
> know that no more time has been left.  Then, pass 0 timeout value to
> intel_uc_wait_for_idle() to give it a chance to return success if GuC is
> already idle.
> 
> 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 at linux.intel.com>
> Cc: stable at vger.kernel.org # v5.15+
> ---
>  drivers/gpu/drm/i915/gt/intel_gt.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c b/drivers/gpu/drm/i915/gt/
intel_gt.c
> index 0325f071046ca..5d612ba547d23 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt.c
> @@ -677,8 +677,15 @@ 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 == -ETIME)
> +		remaining_timeout = 0;
> +	else if (remaining_timeout < 0)
> +		return remaining_timeout;
> +
> +	return intel_uc_wait_for_idle(&gt->uc, remaining_timeout);
>  }
>  
>  int intel_gt_init(struct intel_gt *gt)
>