drm/amdgpu: get absolute offset from doorbell index

This patch adds a helper function which converts a doorbell's
relative index in a BO to an absolute doorbell offset in the
doorbell BAR.

V2: No space between the variable name doc (Luben)

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian Koenig <christian.koenig@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Shashank Sharma <shashank.sharma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_doorbell.h

@@ -356,6 +356,9 @@ void amdgpu_mm_wdoorbell64(struct amdgpu_device *adev, u32 index, u64 v);
 int amdgpu_doorbell_init(struct amdgpu_device *adev);
 void amdgpu_doorbell_fini(struct amdgpu_device *adev);
 int amdgpu_doorbell_create_kernel_doorbells(struct amdgpu_device *adev);
+uint32_t amdgpu_doorbell_index_on_bar(struct amdgpu_device *adev,
+				       struct amdgpu_bo *db_bo,
+				       uint32_t doorbell_index);
 
 #define RDOORBELL32(index) amdgpu_mm_rdoorbell(adev, (index))
 #define WDOORBELL32(index, v) amdgpu_mm_wdoorbell(adev, (index), (v))

drivers/gpu/drm/amd/amdgpu/amdgpu_doorbell_mgr.c

@@ -108,6 +108,27 @@ void amdgpu_mm_wdoorbell64(struct amdgpu_device *adev, u32 index, u64 v)
 		DRM_ERROR("writing beyond doorbell aperture: 0x%08x!\n", index);
 }
 
+/**
+ * amdgpu_doorbell_index_on_bar - Find doorbell's absolute offset in BAR
+ *
+ * @adev: amdgpu_device pointer
+ * @db_bo: doorbell object's bo
+ * @db_index: doorbell relative index in this doorbell object
+ *
+ * returns doorbell's absolute index in BAR
+ */
+uint32_t amdgpu_doorbell_index_on_bar(struct amdgpu_device *adev,
+				       struct amdgpu_bo *db_bo,
+				       uint32_t doorbell_index)
+{
+	int db_bo_offset;
+
+	db_bo_offset = amdgpu_bo_gpu_offset_no_check(db_bo);
+
+	/* doorbell index is 32 bit but doorbell's size is 64-bit, so *2 */
+	return db_bo_offset / sizeof(u32) + doorbell_index * 2;
+}
+
 /**
  * amdgpu_doorbell_create_kernel_doorbells - Create kernel doorbells for graphics
  *