[Intel-gfx] [PATCH v3 4/4] drm/i915: Acquire PUNIT->PMIC bus for intel_uncore_forcewake_reset()

Thu Aug 17 12:22:06 UTC 2017

On Mon, Aug 14, 2017 at 09:58:32PM +0200, Hans de Goede wrote:
> intel_uncore_forcewake_reset() does forcewake puts and gets as such
> we need to make sure that no-one tries to access the PUNIT->PMIC bus
> (on systems where this bus is shared) while it runs, otherwise bad
> things happen.
> 
> Normally this is taken care of by the i915_pmic_bus_access_notifier()
> which does an intel_uncore_forcewake_get(FORCEWAKE_ALL) when some other
> driver tries to access the PMIC bus, so that later forcewake gets are
> no-ops (for the duration of the bus access).
> 
> But intel_uncore_forcewake_reset gets called in 3 cases:
> 1) Before registering the pmic_bus_access_notifier
> 2) After unregistering the pmic_bus_access_notifier
> 3) To reset forcewake state on a GPU reset
> 
> In all 3 cases the i915_pmic_bus_access_notifier() protection is
> insufficient.
> 
> This commit fixes this race by calling iosf_mbi_punit_acquire() before
> calling intel_uncore_forcewake_reset(). In the case where it is called
> directly after unregistering the pmic_bus_access_notifier, we need to
> hold the punit-lock over both calls to avoid a race where
> intel_uncore_fw_release_timer() may execute between the 2 calls.
> 
> To allow holding the lock over both calls we need an unlocked
> variant of iosf_mbi_unregister_pmic_bus_access_notifier. Since
> intel_uncore.c is the only user of this function, we simply
> modify it in this commit. Doing this in a separate commit would
> require first adding an unlocked variant, then this commit and
> then removing the unused normal variant.
> 
> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> ---
> Changes in v2:
> -Rebase on current (July 6th 2017) drm-next
> 
> Changes in v3:
> -Keep punit acquired / locked over the unregister + forcewake_reset
>  call combo to avoid a race hitting between the 2 calls
> -This requires modifying iosf_mbi_unregister_pmic_bus_access_notifier
>  to not take the lock itself, since we are the only users this is done
>  in this same commit
> ---
>  arch/x86/include/asm/iosf_mbi.h     | 10 ++++++++--
>  arch/x86/platform/intel/iosf_mbi.c  | 14 +++++---------
>  drivers/gpu/drm/i915/intel_uncore.c | 17 +++++++++++++----
>  3 files changed, 26 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/include/asm/iosf_mbi.h b/arch/x86/include/asm/iosf_mbi.h
> index c313cac36f56..f8841bb06d98 100644
> --- a/arch/x86/include/asm/iosf_mbi.h
> +++ b/arch/x86/include/asm/iosf_mbi.h
> @@ -141,9 +141,14 @@ int iosf_mbi_register_pmic_bus_access_notifier(struct notifier_block *nb);
>  /**
>   * iosf_mbi_register_pmic_bus_access_notifier - Unregister PMIC bus notifier

You missed the rename in the doc.

>   *
> + * Note the caller must call iosf_mbi_punit_acquire() before calling this
> + * to ensure the bus is inactive before unregistering (and call
> + * iosf_mbi_punit_release() afterwards).
> + *
>   * @nb: notifier_block to unregister
>   */
> -int iosf_mbi_unregister_pmic_bus_access_notifier(struct notifier_block *nb);
> +int iosf_mbi_unregister_pmic_bus_access_notifier_unlocked(
> +	struct notifier_block *nb);
>  
>  /**
>   * iosf_mbi_call_pmic_bus_access_notifier_chain - Call PMIC bus notifier chain
> @@ -191,7 +196,8 @@ int iosf_mbi_register_pmic_bus_access_notifier(struct notifier_block *nb)
>  }
>  
>  static inline
> -int iosf_mbi_unregister_pmic_bus_access_notifier(struct notifier_block *nb)
> +int iosf_mbi_unregister_pmic_bus_access_notifier_unlocked(
> +	struct notifier_block *nb)
>  {
>  	return 0;
>  }
> diff --git a/arch/x86/platform/intel/iosf_mbi.c b/arch/x86/platform/intel/iosf_mbi.c
> index a952ac199741..5596a3ec1b89 100644
> --- a/arch/x86/platform/intel/iosf_mbi.c
> +++ b/arch/x86/platform/intel/iosf_mbi.c
> @@ -218,19 +218,15 @@ int iosf_mbi_register_pmic_bus_access_notifier(struct notifier_block *nb)
>  }
>  EXPORT_SYMBOL(iosf_mbi_register_pmic_bus_access_notifier);
>  
> -int iosf_mbi_unregister_pmic_bus_access_notifier(struct notifier_block *nb)
> +int iosf_mbi_unregister_pmic_bus_access_notifier_unlocked(
> +	struct notifier_block *nb)
>  {
> -	int ret;
> +	WARN_ON(!mutex_is_locked(&iosf_mbi_punit_mutex));
>  
> -	/* Wait for the bus to go inactive before unregistering */
> -	mutex_lock(&iosf_mbi_punit_mutex);
> -	ret = blocking_notifier_chain_unregister(
> +	return blocking_notifier_chain_unregister(
>  				&iosf_mbi_pmic_bus_access_notifier, nb);
> -	mutex_unlock(&iosf_mbi_punit_mutex);
> -
> -	return ret;
>  }
> -EXPORT_SYMBOL(iosf_mbi_unregister_pmic_bus_access_notifier);
> +EXPORT_SYMBOL(iosf_mbi_unregister_pmic_bus_access_notifier_unlocked);
>  
>  int iosf_mbi_call_pmic_bus_access_notifier_chain(unsigned long val, void *v)
>  {
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 569d115918eb..7be6150520ed 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -229,6 +229,7 @@ intel_uncore_fw_release_timer(struct hrtimer *timer)
>  	return HRTIMER_NORESTART;
>  }
>  
> +/* Note callers must have acquired the PUNIT->PMIC bus, before calling this. */

Nit: could use an iosf_assert_mbi_punit_mutex_held() helper instead of
the comment. (taking CONFIG_IOSF_MBI into account)

>  static void intel_uncore_forcewake_reset(struct drm_i915_private *dev_priv,
>  					 bool restore)
>  {
> @@ -416,14 +417,18 @@ static void __intel_uncore_early_sanitize(struct drm_i915_private *dev_priv,
>  				   GT_FIFO_CTL_RC6_POLICY_STALL);
>  	}
>  
> +	iosf_mbi_punit_acquire();
>  	intel_uncore_forcewake_reset(dev_priv, restore_forcewake);
> +	iosf_mbi_punit_release();
>  }
>  
>  void intel_uncore_suspend(struct drm_i915_private *dev_priv)
>  {
> -	iosf_mbi_unregister_pmic_bus_access_notifier(
> +	iosf_mbi_punit_acquire();
> +	iosf_mbi_unregister_pmic_bus_access_notifier_unlocked(
>  		&dev_priv->uncore.pmic_bus_access_nb);
>  	intel_uncore_forcewake_reset(dev_priv, false);
> +	iosf_mbi_punit_release();
>  }
>  
>  void intel_uncore_resume_early(struct drm_i915_private *dev_priv)
> @@ -1246,12 +1251,14 @@ void intel_uncore_init(struct drm_i915_private *dev_priv)
>  
>  void intel_uncore_fini(struct drm_i915_private *dev_priv)
>  {
> -	iosf_mbi_unregister_pmic_bus_access_notifier(
> -		&dev_priv->uncore.pmic_bus_access_nb);
> -
>  	/* Paranoia: make sure we have disabled everything before we exit. */
>  	intel_uncore_sanitize(dev_priv);
> +
> +	iosf_mbi_punit_acquire();
> +	iosf_mbi_unregister_pmic_bus_access_notifier_unlocked(
> +		&dev_priv->uncore.pmic_bus_access_nb);
>  	intel_uncore_forcewake_reset(dev_priv, false);
> +	iosf_mbi_punit_release();
>  }
>  
>  #define GEN_RANGE(l, h) GENMASK((h) - 1, (l) - 1)
> @@ -1524,7 +1531,9 @@ static int gen6_reset_engines(struct drm_i915_private *dev_priv,
>  
>  	ret = gen6_hw_domain_reset(dev_priv, hw_mask);
>  
> +	iosf_mbi_punit_acquire();
>  	intel_uncore_forcewake_reset(dev_priv, true);
> +	iosf_mbi_punit_release();
>  
>  	return ret;
>  }

There is one more spot in intel_uncore_check_forcewake_domains() calling
intel_uncore_forcewake_reset() you missed.

With the above fixes and optional change for the nit looks ok:
Reviewed-by: Imre Deak <imre.deak at intel.com>

> -- 
> 2.13.4
> 