drm/i915: check for ERR_PTR from i915_gem_object_pin_map()

The newly-introduced function i915_gem_object_pin_map() returns an
ERR_PTR (not NULL) if the pin-and-map opertaion fails, so that's what we
must check for. And it's nicer not to assign such a pointer-or-error to
a structure being filled in until after it's been validated, so we
should keep it local and avoid exporting a bogus pointer. Also, for
clarity and symmetry, we should clear 'virtual_start' along with 'vma'
when unmapping a ringbuffer.

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 85102ad75962..6f1e0f127c0a 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3018,9 +3018,11 @@ static inline void i915_gem_object_unpin_pages(struct drm_i915_gem_object *obj)
  * pages and then returns a contiguous mapping of the backing storage into
  * the kernel address space.
  *
- * The caller must hold the struct_mutex.
+ * The caller must hold the struct_mutex, and is responsible for calling
+ * i915_gem_object_unpin_map() when the mapping is no longer required.
  *
- * Returns the pointer through which to access the backing storage.
+ * Returns the pointer through which to access the mapped object, or an
+ * ERR_PTR() on error.
  */
 void *__must_check i915_gem_object_pin_map(struct drm_i915_gem_object *obj);