Re: [PATCH] drm/i915: Don't fail rpm suspend with -EGAIN

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Nov 17, 2015 at 10:18:41PM +0100, Daniel Vetter wrote:
> If we can't acquire dev->struct_mutex we need to fail runtime suspend,
> at least with the current design. Currently we do that using -EAGAIN,
> but that upsets the pm core, resulting in the occasional fail testcase
> in our CI with the following dmesg dirt:
> 
> pci_pm_runtime_suspend(): intel_runtime_suspend+0x0/0x240 [i915] returns -11
> 
> Chris has some ideas to improve this, but for now just shut up the
> error.
> 
> Cc: Paulo Zanoni <przanoni@gmail.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index 5a70aca71d6b..ab8ffbc48e2d 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -1497,8 +1497,7 @@ static int intel_runtime_suspend(struct device *device)
>  	 * We could deadlock here in case another thread holding struct_mutex
>  	 * calls RPM suspend concurrently, since the RPM suspend will wait
>  	 * first for this RPM suspend to finish. In this case the concurrent
> -	 * RPM resume will be followed by its RPM suspend counterpart. Still
> -	 * for consistency return -EAGAIN, which will reschedule this suspend.
> +	 * RPM resume will be followed by its RPM suspend counterpart.
>  	 */
>  	if (!mutex_trylock(&dev->struct_mutex)) {
>  		DRM_DEBUG_KMS("device lock contention, deffering suspend\n");
> @@ -1508,7 +1507,8 @@ static int intel_runtime_suspend(struct device *device)
>  		 */
>  		pm_runtime_mark_last_busy(device);
>  
> -		return -EAGAIN;
> +		/* Fail silently to avoid upsetting the pm core. */
> +		return 0;

So the core will assume we're now suspended and then resume gets called
while we're still powered on. Sounds like a bad plan to me. I'm
especially worried about VLV here with its GT no wake dance and manual
save/restore.

>  	}
>  	/*
>  	 * We are safe here against re-faults, since the fault handler takes
> -- 
> 2.5.1
> 
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-- 
Ville Syrjälä
Intel OTC
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