drm/amdgpu: fix&cleanups for wb_clear

fix:
should do right shift on wb before clearing

cleanups:
1,should memset all wb buffer
2,set max wb number to 128 (total 4KB) is big enough
Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1072,7 +1072,7 @@ static inline void amdgpu_set_ib_value(struct amdgpu_cs_parser *p,
 /*
  * Writeback
  */
-#define AMDGPU_MAX_WB 512	/* Reserve at most 512 WB slots for amdgpu-owned rings. */
+#define AMDGPU_MAX_WB 128	/* Reserve at most 128 WB slots for amdgpu-owned rings. */
 
 struct amdgpu_wb {
 	struct amdgpu_bo	*wb_obj;

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

@@ -492,7 +492,7 @@ static int amdgpu_device_wb_init(struct amdgpu_device *adev)
 		memset(&adev->wb.used, 0, sizeof(adev->wb.used));
 
 		/* clear wb memory */
-		memset((char *)adev->wb.wb, 0, AMDGPU_MAX_WB * sizeof(uint32_t));
+		memset((char *)adev->wb.wb, 0, AMDGPU_MAX_WB * sizeof(uint32_t) * 8);
 	}
 
 	return 0;
@@ -530,8 +530,9 @@ int amdgpu_device_wb_get(struct amdgpu_device *adev, u32 *wb)
  */
 void amdgpu_device_wb_free(struct amdgpu_device *adev, u32 wb)
 {
+	wb >>= 3;
 	if (wb < adev->wb.num_wb)
-		__clear_bit(wb >> 3, adev->wb.used);
+		__clear_bit(wb, adev->wb.used);
 }
 
 /**