[Intel-gfx] [PATCH] drm/i915: Disable mmio debugging during user access

[Chris Wilson]

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 at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at 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);
 
 	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