Re: [PATCH] drm/i915: Disable mmio debugging during user access

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> If the user bypasses i915 and accesses mmio directly, that easily
> confuses our automatic mmio debugging (any error we then detect is
> likely to be as a result of the user). Since we expect userspace to open
> debugfs/i915_forcewake_user if i915.ko is loaded and they want mmio
> access, that makes the opportune time to disable our debugging for
> duration of the bypass.
>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=102543
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c | 32 ++++++++++++++++++++++++++++++--
>  drivers/gpu/drm/i915/intel_uncore.h |  7 +++++++
>  2 files changed, 37 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 48572b157222..d63b3c5c2f83 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -4679,7 +4679,21 @@ static int i915_forcewake_open(struct inode *inode, struct file *file)
>  		return 0;
>  
>  	intel_runtime_pm_get(dev_priv);
> -	intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);
> +
> +	spin_lock_irq(&dev_priv->uncore.lock);
> +	if (!dev_priv->uncore.user_forcewake.count++) {
> +		intel_uncore_forcewake_get__locked(dev_priv, FORCEWAKE_ALL);
> +
> +		/* Save and disable mmio debugging for the user bypass */
> +		dev_priv->uncore.user_forcewake.saved_mmio_check =
> +			dev_priv->uncore.unclaimed_mmio_check;
> +		dev_priv->uncore.user_forcewake.saved_mmio_debug =
> +			i915.mmio_debug;
> +
> +		dev_priv->uncore.unclaimed_mmio_check = 0;
> +		i915.mmio_debug = 0;
> +	}
> +	spin_unlock_irq(&dev_priv->uncore.lock);

Just pondering if this should be in intel_uncore.c as a
user_mmio_bypass_on/off(). But not insisting.

Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>

>  
>  	return 0;
>  }
> @@ -4691,7 +4705,21 @@ static int i915_forcewake_release(struct inode *inode, struct file *file)
>  	if (INTEL_GEN(dev_priv) < 6)
>  		return 0;
>  
> -	intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);
> +	spin_lock_irq(&dev_priv->uncore.lock);
> +	if (!--dev_priv->uncore.user_forcewake.count) {
> +		if (intel_uncore_unclaimed_mmio(dev_priv))
> +			dev_info(dev_priv->drm.dev,
> +				 "Unclaimed mmio occurred during user acess\n");
> +
> +		dev_priv->uncore.unclaimed_mmio_check =
> +			dev_priv->uncore.user_forcewake.saved_mmio_check;
> +		i915.mmio_debug =
> +			dev_priv->uncore.user_forcewake.saved_mmio_debug;
> +
> +		intel_uncore_forcewake_put__locked(dev_priv, FORCEWAKE_ALL);
> +	}
> +	spin_unlock_irq(&dev_priv->uncore.lock);
> +
>  	intel_runtime_pm_put(dev_priv);
>  
>  	return 0;
> diff --git a/drivers/gpu/drm/i915/intel_uncore.h b/drivers/gpu/drm/i915/intel_uncore.h
> index 5f90278da461..1acf24c6e9ce 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.h
> +++ b/drivers/gpu/drm/i915/intel_uncore.h
> @@ -102,6 +102,13 @@ struct intel_uncore {
>  		i915_reg_t reg_ack;
>  	} fw_domain[FW_DOMAIN_ID_COUNT];
>  
> +	struct {
> +		unsigned int count;
> +
> +		int saved_mmio_check;
> +		int saved_mmio_debug;
> +	} user_forcewake;
> +
>  	int unclaimed_mmio_check;
>  };
>  
> -- 
> 2.14.1
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