Re: [PATCH 09/10] drm/i915: add support for checking RPM atomic sections

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

On ti, 2015-12-15 at 20:10 +0200, Imre Deak wrote:
> In some cases we want to check whether we hold an RPM wakelock
> reference
> for the whole duration of a sequence. To achieve this add a new RPM
> atomic sequence
> counter that we increment any time the wakelock refcount drops to
> zero.
> Check whether the sequence number stays the same during the atomic
> section and that we hold the wakelock at the beginning of the
> section.
> 
> Motivated by Chris.
> 
> v2-v3:
> - unchanged
> v4:
> - swap the order of atomic_read() and assert_rpm_wakelock_held() in
>   assert_rpm_atomic_begin() to avoid race
> 
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> (v3)

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/i915_drv.h         |  1 +
>  drivers/gpu/drm/i915/intel_drv.h        | 17 +++++++++++++++++
>  drivers/gpu/drm/i915/intel_pm.c         |  1 +
>  drivers/gpu/drm/i915/intel_runtime_pm.c |  3 ++-
>  4 files changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h
> b/drivers/gpu/drm/i915/i915_drv.h
> index 2894716..00ce627 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1603,6 +1603,7 @@ struct skl_wm_level {
>   */
>  struct i915_runtime_pm {
>  	atomic_t wakeref_count;
> +	atomic_t atomic_seq;
>  	bool suspended;
>  	bool irqs_enabled;
>  };
> diff --git a/drivers/gpu/drm/i915/intel_drv.h
> b/drivers/gpu/drm/i915/intel_drv.h
> index d8e4aca..88d37eb 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -1446,6 +1446,23 @@ assert_rpm_wakelock_held(struct
> drm_i915_private *dev_priv)
>  		  "RPM wakelock ref not held during HW access");
>  }
>  
> +static inline int
> +assert_rpm_atomic_begin(struct drm_i915_private *dev_priv)
> +{
> +	int seq = atomic_read(&dev_priv->pm.atomic_seq);
> +
> +	assert_rpm_wakelock_held(dev_priv);
> +
> +	return seq;
> +}
> +
> +static inline void
> +assert_rpm_atomic_end(struct drm_i915_private *dev_priv, int
> begin_seq)
> +{
> +	WARN_ONCE(atomic_read(&dev_priv->pm.atomic_seq) !=
> begin_seq,
> +		 "HW access outside of RPM atomic section\n");
> +}
> +
>  /**
>   * disable_rpm_wakeref_asserts - disable the RPM assert checks
>   * @dev_priv: i915 device instance
> diff --git a/drivers/gpu/drm/i915/intel_pm.c
> b/drivers/gpu/drm/i915/intel_pm.c
> index 6c08537..6eb9606 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -7248,4 +7248,5 @@ void intel_pm_setup(struct drm_device *dev)
>  
>  	dev_priv->pm.suspended = false;
>  	atomic_set(&dev_priv->pm.wakeref_count, 0);
> +	atomic_set(&dev_priv->pm.atomic_seq, 0);
>  }
> diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c
> b/drivers/gpu/drm/i915/intel_runtime_pm.c
> index 82c55a9..cee54ea 100644
> --- a/drivers/gpu/drm/i915/intel_runtime_pm.c
> +++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
> @@ -2283,7 +2283,8 @@ void intel_runtime_pm_put(struct
> drm_i915_private *dev_priv)
>  	struct device *device = &dev->pdev->dev;
>  
>  	assert_rpm_wakelock_held(dev_priv);
> -	atomic_dec(&dev_priv->pm.wakeref_count);
> +	if (atomic_dec_and_test(&dev_priv->pm.wakeref_count))
> +		atomic_inc(&dev_priv->pm.atomic_seq);
>  
>  	pm_runtime_mark_last_busy(device);
>  	pm_runtime_put_autosuspend(device);
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation

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