Re: [PATCH v12 04/11] drm/i915: Create uC runtime and system suspend/resume helpers

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

+ Michal,

On the principle of code motion first, changes second, I'd like to see
the clean split-up from Michal before touching the files much. That way
 git history will be easier to examine.

Few comments below.

On Thu, 2017-09-28 at 12:18 +0530, Sagar Arun Kamble wrote:
> Prepared generic helpers intel_uc_suspend, intel_uc_resume,
> intel_uc_runtime_suspend, intel_uc_runtime_resume. These are
> called from respective GEM functions.
> Only exception is intel_uc_resume that needs to be called
> w/ or w/o GuC loaded in i915_drm_resume path. Changes to
> add WOPCM condition check to load GuC during resume will be added
> in later patches.
> 
> v2: Rebase w.r.t removal of GuC code restructuring.
> 
> v3: Calling intel_uc_resume from i915_gem_resume post resuming
> i915 gem setup. This is symmetrical with i915_gem_suspend.
> Removed error messages from i915 suspend/resume routines as
> uC suspend/resume routines will have those. (Michal Wajdeczko)
> Declare wedged on uc_suspend failure and uc_resume failure.
> (Michał Winiarski)
> Keeping the uC suspend/resume function definitions close to other
> uC functions.
> 
> v4: Added implementation to intel_uc_resume as GuC resume is
> needed to be triggered post reloading the firmware as well. Added
> comments about semantics of GuC resume with the firmware reload.
> 
> v5: Updated return from i915_gem_runtime_suspend. Moved the comment
> about GuC reload optimization to intel_uc_init_hw. (Michal Wajdeczko)
> Updated comments as FIXME.
> 
> Signed-off-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
> Cc: Michał Winiarski <michal.winiarski@intel.com>

<SNIP>

> @@ -1698,6 +1698,18 @@ static int i915_drm_resume(struct drm_device *dev)
>  	}
>  	mutex_unlock(&dev->struct_mutex);
>  
> +	/*
> +	 * FIXME: Currently we know that at the end of suspend we have done Full

I think "beginning of resume" is the one that bites us more.

> +	 * GPU reset and GuC is loaded again during i915_gem_init_hw.
> +	 * Now, send action to GuC to resume back again as earlier call to
> +	 * intel_uc_resume from i915_gem_resume would have done nothing.
> +	 * This needs to be skipped if GuC was not loaded during resume as
> +	 * intel_uc_resume would have been already called from i915_gem_resume.
> +	 */
> +	ret = intel_uc_resume(dev_priv);
> +	if (ret)
> +		i915_gem_set_wedged(dev_priv);

I'm very sure we want to bring the system up with a backup of ELSP only
submission *even* if we used GuC when going to sleep.

> @@ -4571,7 +4573,9 @@ int i915_gem_suspend(struct drm_i915_private *dev_priv)
>  	if (WARN_ON(!intel_engines_are_idle(dev_priv)))
>  		i915_gem_set_wedged(dev_priv); /* no hope, discard everything */
>  
> -	intel_guc_suspend(dev_priv);
> +	ret = intel_uc_suspend(dev_priv);
> +	if (ret)
> +		i915_gem_set_wedged(dev_priv); /* no hope, discard everything */

Isn't that an exxaragation when we still may have functional ELSP?

It may not be a bad idea to first bring up the ELSP submission and when
GuC has loaded, switch over. To get rid of the latency.

> @@ -4619,7 +4624,16 @@ int i915_gem_resume(struct drm_i915_private *dev_priv)
>  	 */
>  	dev_priv->gt.resume(dev_priv);
>  
> -	intel_guc_resume(dev_priv);
> +	/*
> +	 * FIXME: At the end of suspend, Full GPU reset is done which unloads
> +	 * the GuC firmware. If reset is avoided there, we can check the WOPCM
> +	 * status here to see if GuC is still loaded and just do GuC resume
> +	 * without reloading the firmware back.
> +	 */

Again, we're resetting at both directions, going to suspend and on
resume too. I'd classify these bot as more of a TODOs, because we only
get some latency that can be improved on, no broken behaviour to fix.

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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