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>

2 files changed, 13 insertions, 8 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);
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 978f0b676c68..245386e20c52 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2088,6 +2088,7 @@ void intel_unpin_ringbuffer_obj(struct intel_ringbuffer *ringbuf)
                 i915_gem_object_unpin_map(ringbuf->obj);
         else
                 iounmap(ringbuf->virtual_start);
+        ringbuf->virtual_start = NULL;
         ringbuf->vma = NULL;
         i915_gem_object_ggtt_unpin(ringbuf->obj);
 }
@@ -2100,6 +2101,7 @@ int intel_pin_and_map_ringbuffer_obj(struct drm_device *dev,
         struct drm_i915_gem_object *obj = ringbuf->obj;
         /* Ring wraparound at offset 0 sometimes hangs. No idea why. */
         unsigned flags = PIN_OFFSET_BIAS | 4096;
+        void *addr;
         int ret;
 
         if (HAS_LLC(dev_priv) && !obj->stolen) {
@@ -2111,9 +2113,9 @@ int intel_pin_and_map_ringbuffer_obj(struct drm_device *dev,
                 if (ret)
                         goto err_unpin;
 
-                ringbuf->virtual_start = i915_gem_object_pin_map(obj);
-                if (ringbuf->virtual_start == NULL) {
-                        ret = -ENOMEM;
+                addr = i915_gem_object_pin_map(obj);
+                if (IS_ERR(addr)) {
+                        ret = PTR_ERR(addr);
                         goto err_unpin;
                 }
         } else {
@@ -2129,14 +2131,15 @@ int intel_pin_and_map_ringbuffer_obj(struct drm_device *dev,
                 /* Access through the GTT requires the device to be awake. */
                 assert_rpm_wakelock_held(dev_priv);
 
-                ringbuf->virtual_start = ioremap_wc(ggtt->mappable_base +
-                                                    i915_gem_obj_ggtt_offset(obj), ringbuf->size);
-                if (ringbuf->virtual_start == NULL) {
+                addr = ioremap_wc(ggtt->mappable_base +
+                                  i915_gem_obj_ggtt_offset(obj), ringbuf->size);
+                if (addr == NULL) {
                         ret = -ENOMEM;
                         goto err_unpin;
                 }
         }
 
+        ringbuf->virtual_start = addr;
         ringbuf->vma = i915_gem_obj_to_ggtt(obj);
         return 0;