drm/i915: Disable mmio debugging during user access

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.

v2: Move the fiddling of uncore internals to uncore.c

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>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170907134441.12881-1-chris@chris-wilson.co.uk

3 files changed, 72 insertions, 8 deletions

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 8d432e50a196..6338018f655d 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -1421,6 +1421,9 @@ static int i915_forcewake_domains(struct seq_file *m, void *data)
 	struct intel_uncore_forcewake_domain *fw_domain;
 	unsigned int tmp;
 
+	seq_printf(m, "user.bypass_count = %u\n",
+		   i915->uncore.user_forcewake.count);
+
 	for_each_fw_domain(fw_domain, i915, tmp)
 		seq_printf(m, "%s.wake_count = %u\n",
 			   intel_uncore_forcewake_domain_to_str(fw_domain->id),
@@ -4724,26 +4727,26 @@ static int i915_sseu_status(struct seq_file *m, void *unused)
 
 static int i915_forcewake_open(struct inode *inode, struct file *file)
 {
-	struct drm_i915_private *dev_priv = inode->i_private;
+	struct drm_i915_private *i915 = inode->i_private;
 
-	if (INTEL_GEN(dev_priv) < 6)
+	if (INTEL_GEN(i915) < 6)
 		return 0;
 
-	intel_runtime_pm_get(dev_priv);
-	intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);
+	intel_runtime_pm_get(i915);
+	intel_uncore_forcewake_user_get(i915);
 
 	return 0;
 }
 
 static int i915_forcewake_release(struct inode *inode, struct file *file)
 {
-	struct drm_i915_private *dev_priv = inode->i_private;
+	struct drm_i915_private *i915 = inode->i_private;
 
-	if (INTEL_GEN(dev_priv) < 6)
+	if (INTEL_GEN(i915) < 6)
 		return 0;
 
-	intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);
-	intel_runtime_pm_put(dev_priv);
+	intel_uncore_forcewake_user_put(i915);
+	intel_runtime_pm_put(i915);
 
 	return 0;
 }
diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index 0529af7cfbb8..1b38eb94d461 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -490,6 +490,57 @@ void intel_uncore_forcewake_get(struct drm_i915_private *dev_priv,
 }
 
 /**
+ * intel_uncore_forcewake_user_get - claim forcewake on behalf of userspace
+ * @dev_priv: i915 device instance
+ *
+ * This function is a wrapper around intel_uncore_forcewake_get() to acquire
+ * the GT powerwell and in the process disable our debugging for the
+ * duration of userspace's bypass.
+ */
+void intel_uncore_forcewake_user_get(struct drm_i915_private *dev_priv)
+{
+	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);
+}
+
+/**
+ * intel_uncore_forcewake_user_put - release forcewake on behalf of userspace
+ * @dev_priv: i915 device instance
+ *
+ * This function complements intel_uncore_forcewake_user_get() and releases
+ * the GT powerwell taken on behalf of the userspace bypass.
+ */
+void intel_uncore_forcewake_user_put(struct drm_i915_private *dev_priv)
+{
+	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,
+				 "Invalid mmio detected during user access\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_uncore_forcewake_get__locked - grab forcewake domain references
  * @dev_priv: i915 device instance
  * @fw_domains: forcewake domains to get reference on
diff --git a/drivers/gpu/drm/i915/intel_uncore.h b/drivers/gpu/drm/i915/intel_uncore.h
index 5f90278da461..03786f931905 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;
 };
 
@@ -144,6 +151,9 @@ void intel_uncore_forcewake_get__locked(struct drm_i915_private *dev_priv,
 void intel_uncore_forcewake_put__locked(struct drm_i915_private *dev_priv,
 					enum forcewake_domains domains);
 
+void intel_uncore_forcewake_user_get(struct drm_i915_private *dev_priv);
+void intel_uncore_forcewake_user_put(struct drm_i915_private *dev_priv);
+
 int intel_wait_for_register(struct drm_i915_private *dev_priv,
 			    i915_reg_t reg,
 			    u32 mask,