drm/i915: Emphasize that ctx->id is merely a user handle

This is an Execlists preparatory patch, since they make context ID become an
overloaded term:

- In the software, it was used to distinguish which context userspace was
  trying to use.
- In the BSpec, the term is used to describe the 20-bits long field the
  hardware uses to it to discriminate the contexts that are submitted to
  the ELSP and inform the driver about their current status (via Context
  Switch Interrupts and Context Status Buffers).

Initially, I tried to make the different meanings converge, but it proved
impossible:

- The software ctx->id is per-filp, while the hardware one needs to be
  globally unique.
- Also, we multiplex several backing states objects per intel_context,
  and all of them need unique HW IDs.
- I tried adding a per-filp ID and then composing the HW context ID as:
  ctx->id + file_priv->id + ring->id, but the fact that the hardware only
  uses 20-bits means we have to artificially limit the number of filps or
  contexts the userspace can create.

The ctx->user_handle renaming bits are done with this Cocci patch (plus
manual frobbing of the struct declaration):

    @@
    struct intel_context c;
    @@
    - (c).id
    + c.user_handle

    @@
    struct intel_context *c;
    @@
    - (c)->id
    + c->user_handle

Also, while we are at it, s/DEFAULT_CONTEXT_ID/DEFAULT_CONTEXT_HANDLE and
change the type to unsigned 32 bits.

v2: s/handle/user_handle and change the type to uint32_t as suggested by
Chris Wilson.

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org> (v1)
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1876,7 +1876,7 @@ static int per_file_ctx(int id, void *ptr, void *data)
 	if (i915_gem_context_is_default(ctx))
 		seq_puts(m, "  default context:\n");
 	else
-		seq_printf(m, "  context %d:\n", ctx->id);
+		seq_printf(m, "  context %d:\n", ctx->user_handle);
 	ppgtt->debug_dump(ppgtt, m);
 
 	return 0;

drivers/gpu/drm/i915/i915_drv.h

@@ -585,10 +585,10 @@ struct i915_ctx_hang_stats {
 };
 
 /* This must match up with the value previously used for execbuf2.rsvd1. */
-#define DEFAULT_CONTEXT_ID 0
+#define DEFAULT_CONTEXT_HANDLE 0
 struct intel_context {
 	struct kref ref;
-	int id;
+	int user_handle;
 	uint8_t remap_slice;
 	struct drm_i915_file_private *file_priv;
 	struct i915_ctx_hang_stats hang_stats;
@@ -2469,7 +2469,7 @@ static inline void i915_gem_context_unreference(struct intel_context *ctx)
 
 static inline bool i915_gem_context_is_default(const struct intel_context *c)
 {
-	return c->id == DEFAULT_CONTEXT_ID;
+	return c->user_handle == DEFAULT_CONTEXT_HANDLE;
 }
 
 int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,

drivers/gpu/drm/i915/i915_gem_context.c

@@ -276,14 +276,14 @@ __create_hw_context(struct drm_device *dev,
 	/* Default context will never have a file_priv */
 	if (file_priv != NULL) {
 		ret = idr_alloc(&file_priv->context_idr, ctx,
-				DEFAULT_CONTEXT_ID, 0, GFP_KERNEL);
+				DEFAULT_CONTEXT_HANDLE, 0, GFP_KERNEL);
 		if (ret < 0)
 			goto err_out;
 	} else
-		ret = DEFAULT_CONTEXT_ID;
+		ret = DEFAULT_CONTEXT_HANDLE;
 
 	ctx->file_priv = file_priv;
-	ctx->id = ret;
+	ctx->user_handle = ret;
 	/* NB: Mark all slices as needing a remap so that when the context first
 	 * loads it will restore whatever remap state already exists. If there
 	 * is no remap info, it will be a NOP. */
@@ -793,7 +793,7 @@ int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,
 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);
 
-	args->ctx_id = ctx->id;
+	args->ctx_id = ctx->user_handle;
 	DRM_DEBUG_DRIVER("HW context %d created\n", args->ctx_id);
 
 	return 0;
@@ -807,7 +807,7 @@ int i915_gem_context_destroy_ioctl(struct drm_device *dev, void *data,
 	struct intel_context *ctx;
 	int ret;
 
-	if (args->ctx_id == DEFAULT_CONTEXT_ID)
+	if (args->ctx_id == DEFAULT_CONTEXT_HANDLE)
 		return -ENOENT;
 
 	ret = i915_mutex_lock_interruptible(dev);
@@ -820,7 +820,7 @@ int i915_gem_context_destroy_ioctl(struct drm_device *dev, void *data,
 		return PTR_ERR(ctx);
 	}
 
-	idr_remove(&ctx->file_priv->context_idr, ctx->id);
+	idr_remove(&ctx->file_priv->context_idr, ctx->user_handle);
 	i915_gem_context_unreference(ctx);
 	mutex_unlock(&dev->struct_mutex);
 

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -938,7 +938,7 @@ i915_gem_validate_context(struct drm_device *dev, struct drm_file *file,
 	struct intel_context *ctx = NULL;
 	struct i915_ctx_hang_stats *hs;
 
-	if (ring->id != RCS && ctx_id != DEFAULT_CONTEXT_ID)
+	if (ring->id != RCS && ctx_id != DEFAULT_CONTEXT_HANDLE)
 		return ERR_PTR(-EINVAL);
 
 	ctx = i915_gem_context_get(file->driver_priv, ctx_id);

drivers/gpu/drm/i915/intel_uncore.c

@@ -1010,7 +1010,7 @@ int i915_get_reset_stats_ioctl(struct drm_device *dev,
 	if (args->flags || args->pad)
 		return -EINVAL;
 
-	if (args->ctx_id == DEFAULT_CONTEXT_ID && !capable(CAP_SYS_ADMIN))
+	if (args->ctx_id == DEFAULT_CONTEXT_HANDLE && !capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
 	ret = mutex_lock_interruptible(&dev->struct_mutex);