drm/radeon: add a GPU reset counter queryable by userspace

Userspace will be able to tell whether a GPU reset occured by comparing
an old referece value of the counter with a new value.

Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Marek Olšák <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/radeon/radeon.h

···
 	atomic64_t			vram_usage;
 	atomic64_t			gtt_usage;
 	atomic64_t			num_bytes_moved;
+	atomic_t			gpu_reset_counter;
 	/* ACPI interface */
 	struct radeon_atif		atif;
 	struct radeon_atcs		atcs;

drivers/gpu/drm/radeon/radeon_device.c

···
 		return 0;
 	}
 
+	atomic_inc(&rdev->gpu_reset_counter);
+
 	radeon_save_bios_scratch_regs(rdev);
 	/* block TTM */
 	resched = ttm_bo_lock_delayed_workqueue(&rdev->mman.bdev);

drivers/gpu/drm/radeon/radeon_drv.c

···
  *            CS to GPU on >= r600
  *   2.41.0 - evergreen/cayman: Add SET_BASE/DRAW_INDIRECT command parsing support
  *   2.42.0 - Add VCE/VUI (Video Usability Information) support
+ *   2.43.0 - RADEON_INFO_GPU_RESET_COUNTER
  */
 #define KMS_DRIVER_MAJOR	2
-#define KMS_DRIVER_MINOR	42
+#define KMS_DRIVER_MINOR	43
 #define KMS_DRIVER_PATCHLEVEL	0
 int radeon_driver_load_kms(struct drm_device *dev, unsigned long flags);
 int radeon_driver_unload_kms(struct drm_device *dev);

drivers/gpu/drm/radeon/radeon_kms.c

···
 		if (radeon_get_allowed_info_register(rdev, *value, value))
 			return -EINVAL;
 		break;
+	case RADEON_INFO_GPU_RESET_COUNTER:
+		*value = atomic_read(&rdev->gpu_reset_counter);
+		break;
 	default:
 		DRM_DEBUG_KMS("Invalid request %d\n", info->request);
 		return -EINVAL;

include/uapi/drm/radeon_drm.h

···
 #define RADEON_INFO_CURRENT_GPU_SCLK	0x22
 #define RADEON_INFO_CURRENT_GPU_MCLK	0x23
 #define RADEON_INFO_READ_REG		0x24
+#define RADEON_INFO_GPU_RESET_COUNTER	0x25
 
 struct drm_radeon_info {
 	uint32_t		request;