[RFC 03/34] drm/xe: Fix display runtime_pm handling

[Matthew Auld]

On 26/01/2024 20:30, Rodrigo Vivi wrote:
> i915's intel_runtime_pm_get_if_in_use actually calls the
> pm_runtime_get_if_active() with ign_usage_count = false, but Xe
> was erroneously calling it with true because of the mem_access cases.

Good catch.

> This can lead to unbalanced references.

Is there an actual imbalance here though? Is it not just a case of being 
overzealous in keeping the device awake when it is not currently 
"in_use" vs "if_active"? If the api increments the usage count we will 
still decrement it later, regardless of active vs in-use, AFAICT.

> 
> Let's use directly the 'if_in_use' function provided by linux/pm_runtime.
> 
> Also, already start this new function protected from the runtime
> recursion, since runtime_pm will need to call for display functions
> for a proper D3Cold flow.
> 
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> ---
>   .../gpu/drm/xe/compat-i915-headers/i915_drv.h   |  2 +-
>   drivers/gpu/drm/xe/xe_pm.c                      | 17 +++++++++++++++++
>   drivers/gpu/drm/xe/xe_pm.h                      |  1 +
>   3 files changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/compat-i915-headers/i915_drv.h b/drivers/gpu/drm/xe/compat-i915-headers/i915_drv.h
> index 420eba0e4be0..ad5864d1dd74 100644
> --- a/drivers/gpu/drm/xe/compat-i915-headers/i915_drv.h
> +++ b/drivers/gpu/drm/xe/compat-i915-headers/i915_drv.h
> @@ -177,7 +177,7 @@ static inline intel_wakeref_t intel_runtime_pm_get_if_in_use(struct xe_runtime_p
>   {
>   	struct xe_device *xe = container_of(pm, struct xe_device, runtime_pm);
>   
> -	return xe_pm_runtime_get_if_active(xe);
> +	return xe_pm_runtime_get_if_in_use(xe);
>   }
>   
>   static inline void intel_runtime_pm_put_unchecked(struct xe_runtime_pm *pm)
> diff --git a/drivers/gpu/drm/xe/xe_pm.c b/drivers/gpu/drm/xe/xe_pm.c
> index bd35fe9f6227..19f88cb7715b 100644
> --- a/drivers/gpu/drm/xe/xe_pm.c
> +++ b/drivers/gpu/drm/xe/xe_pm.c
> @@ -417,6 +417,23 @@ int xe_pm_runtime_get_if_active(struct xe_device *xe)
>   	return pm_runtime_get_if_active(xe->drm.dev, true);
>   }
>   
> +/**
> + * xe_pm_runtime_get_if_in_use - Get a runtime_pm reference and resume if needed
> + * @xe: xe device instance
> + *
> + * Returns: True if device is awake and the reference was taken, false otherwise.
> + */
> +bool xe_pm_runtime_get_if_in_use(struct xe_device *xe)
> +{
> +	if (xe_pm_read_callback_task(xe) == current) {
> +		/* The device is awake, grab the ref and move on */
> +		pm_runtime_get_noresume(xe->drm.dev);
> +		return true;
> +	}
> +
> +	return pm_runtime_get_if_in_use(xe->drm.dev) >= 0;

This is doing atomic_inc_not_zero() underneath for the "in_use" case 
AFAICT. If the usage count is zero it doesn't increment it and returns 
0. Does that not lead to an imbalance? Should this rather be > 0?

> +}
> +
>   /**
>    * xe_pm_assert_unbounded_bridge - Disable PM on unbounded pcie parent bridge
>    * @xe: xe device instance
> diff --git a/drivers/gpu/drm/xe/xe_pm.h b/drivers/gpu/drm/xe/xe_pm.h
> index 64a97c6726a7..9d372cbf388b 100644
> --- a/drivers/gpu/drm/xe/xe_pm.h
> +++ b/drivers/gpu/drm/xe/xe_pm.h
> @@ -28,6 +28,7 @@ int xe_pm_runtime_resume(struct xe_device *xe);
>   int xe_pm_runtime_get(struct xe_device *xe);
>   int xe_pm_runtime_put(struct xe_device *xe);
>   int xe_pm_runtime_get_if_active(struct xe_device *xe);
> +bool xe_pm_runtime_get_if_in_use(struct xe_device *xe);
>   void xe_pm_assert_unbounded_bridge(struct xe_device *xe);
>   int xe_pm_set_vram_threshold(struct xe_device *xe, u32 threshold);
>   void xe_pm_d3cold_allowed_toggle(struct xe_device *xe);