drm/i915: Special case default context creation

Previously, the default context was special cased, and not part of the
idr. With the recent PPGTT patches it became ideal to have the default
context simply exist as any other context, and locatable within the idr.
For a future patch, I intend to make it possible to supplant the default
context (see that commit for the details).

Remember that the default context continues to be a special case as its
state is not saved/restored. Therefore if we were to destroy the default
context, and something else ended up with the default context ID, that
context would not have its state saved/restored. That is not correct
behavior.

This patch simple provides the ability to differentiate between a real
default context, and a usurper.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>

1 files changed, 21 insertions, 8 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index ebe0f67eac08..cd15add766bf 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -176,7 +176,8 @@ create_vm_for_ctx(struct drm_device *dev, struct i915_hw_context *ctx)
 
 static struct i915_hw_context *
 __create_hw_context(struct drm_device *dev,
-		  struct drm_i915_file_private *file_priv)
+		  struct drm_i915_file_private *file_priv,
+		  bool default_ctx)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct i915_hw_context *ctx;
@@ -209,8 +210,16 @@ __create_hw_context(struct drm_device *dev,
 	if (file_priv == NULL)
 		return ctx;
 
-	ret = idr_alloc(&file_priv->context_idr, ctx, DEFAULT_CONTEXT_ID, 0,
-			GFP_KERNEL);
+	if (default_ctx) {
+		ret = idr_alloc(&file_priv->context_idr, ctx,
+				DEFAULT_CONTEXT_ID, DEFAULT_CONTEXT_ID,
+				GFP_KERNEL);
+	} else {
+		ret = idr_alloc_cyclic(&file_priv->context_idr, ctx,
+				       DEFAULT_CONTEXT_ID + 1, 0,
+				       GFP_KERNEL);
+	}
+
 	if (ret < 0)
 		goto err_out;
 
@@ -241,7 +250,8 @@ static inline bool is_default_context(struct i915_hw_context *ctx)
 static struct i915_hw_context *
 i915_gem_create_context(struct drm_device *dev,
 			struct drm_i915_file_private *file_priv,
-			bool create_vm)
+			bool create_vm,
+			bool default_ctx)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct i915_hw_context *ctx;
@@ -249,7 +259,7 @@ i915_gem_create_context(struct drm_device *dev,
 
 	BUG_ON(!mutex_is_locked(&dev->struct_mutex));
 
-	ctx = __create_hw_context(dev, file_priv);
+	ctx = __create_hw_context(dev, file_priv, default_ctx);
 	if (IS_ERR(ctx))
 		return ctx;
 
@@ -371,7 +381,8 @@ int i915_gem_context_init(struct drm_device *dev)
 	}
 
 	dev_priv->ring[RCS].default_context =
-		i915_gem_create_context(dev, NULL, USES_ALIASING_PPGTT(dev));
+		i915_gem_create_context(dev, NULL, USES_ALIASING_PPGTT(dev),
+					true);
 
 	if (IS_ERR_OR_NULL(dev_priv->ring[RCS].default_context)) {
 		DRM_DEBUG_DRIVER("Disabling HW Contexts; create failed %ld\n",
@@ -498,7 +509,8 @@ int i915_gem_context_open(struct drm_device *dev, struct drm_file *file)
 
 	mutex_lock(&dev->struct_mutex);
 	file_priv->private_default_ctx =
-		i915_gem_create_context(dev, file_priv, USES_FULL_PPGTT(dev));
+		i915_gem_create_context(dev, file_priv, USES_FULL_PPGTT(dev),
+					true);
 	mutex_unlock(&dev->struct_mutex);
 
 	if (IS_ERR(file_priv->private_default_ctx)) {
@@ -746,7 +758,8 @@ int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,
 	if (ret)
 		return ret;
 
-	ctx = i915_gem_create_context(dev, file_priv, USES_FULL_PPGTT(dev));
+	ctx = i915_gem_create_context(dev, file_priv, USES_FULL_PPGTT(dev),
+				      false);
 	mutex_unlock(&dev->struct_mutex);
 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);