radeon_fence文件源码分析

drivers/gpu/drm/radeon/radeon_fence.c中：

/**
 * radeon_fence_driver_init - init the fence driver
 * for all possible rings.
 *
 * @rdev: radeon device pointer
 *
 * Init the fence driver for all possible rings (all asics).
 * Not all asics have all rings, so each asic will only
 * start the fence driver on the rings it has using
 * radeon_fence_driver_start_ring().
 * Returns 0 for success.
 */
int radeon_fence_driver_init(struct radeon_device *rdev)
{
	int ring;

	init_waitqueue_head(&rdev->fence_queue);
	for (ring = 0; ring < RADEON_NUM_RINGS; ring++) {
		radeon_fence_driver_init_ring(rdev, ring);
	}
	if (radeon_debugfs_fence_init(rdev)) {
		dev_err(rdev->dev, "fence debugfs file creation failed\n");
	}
	return 0;
}

RADEON_NUM_RINGS在drivers/gpu/drm/radeon/radeon.h中定义： 

/* max number of rings */
#define RADEON_NUM_RINGS			8

同文件中：

/**
 * radeon_fence_driver_init_ring - init the fence driver
 * for the requested ring.
 *
 * @rdev: radeon device pointer
 * @ring: ring index to start the fence driver on
 *
 * Init the fence driver for the requested ring (all asics).
 * Helper function for radeon_fence_driver_init().
 */
static void radeon_fence_driver_init_ring(struct radeon_device *rdev, int ring)
{
	int i;

	rdev->fence_drv[ring].scratch_reg = -1;
	rdev->fence_drv[ring].cpu_addr = NULL;
	rdev->fence_drv[ring].gpu_addr = 0;
	for (i = 0; i < RADEON_NUM_RINGS; ++i)
		rdev->fence_drv[ring].sync_seq[i] = 0;
	atomic64_set(&rdev->fence_drv[ring].last_seq, 0);
	rdev->fence_drv[ring].initialized = false;
	INIT_DELAYED_WORK(&rdev->fence_drv[ring].lockup_work,
			  radeon_fence_check_lockup);
	rdev->fence_drv[ring].rdev = rdev;
}

通过INIT_DELAYED_WORK函数创建了一个用于检测死锁的工作队列项，队列项的处理函数为radeon_fence_check_lockup函数。

依旧是同文件（drivers/gpu/drm/radeon/radeon_fence.c）中：

/**
 * radeon_fence_check_lockup - check for hardware lockup
 *
 * @work: delayed work item
 *
 * Checks for fence activity and if there is none probe
 * the hardware if a lockup occured.
 */
static void radeon_fence_check_lockup(struct work_struct *work)
{
	struct radeon_fence_driver *fence_drv;
	struct radeon_device *rdev;
	int ring;

	fence_drv = container_of(work, struct radeon_fence_driver,
				 lockup_work.work);
	rdev = fence_drv->rdev;
	ring = fence_drv - &rdev->fence_drv[0];

	if (!down_read_trylock(&rdev->exclusive_lock)) {
		/* just reschedule the check if a reset is going on */
		radeon_fence_schedule_check(rdev, ring);
		return;
	}

	if (fence_drv->delayed_irq && rdev->ddev->irq_enabled) {
		unsigned long irqflags;

		fence_drv->delayed_irq = false;
		spin_lock_irqsave(&rdev->irq.lock, irqflags);
		radeon_irq_set(rdev);
		spin_unlock_irqrestore(&rdev->irq.lock, irqflags);
	}

	if (radeon_fence_activity(rdev, ring))
		wake_up_all(&rdev->fence_queue);

	else if (radeon_ring_is_lockup(rdev, ring, &rdev->ring[ring])) {

		/* good news we believe it's a lockup */
		dev_warn(rdev->dev, "GPU lockup (current fence id "
			 "0x%016llx last fence id 0x%016llx on ring %d)\n",
			 (uint64_t)atomic64_read(&fence_drv->last_seq),
			 fence_drv->sync_seq[ring], ring);

		/* remember that we need an reset */
		rdev->needs_reset = true;
		wake_up_all(&rdev->fence_queue);
	}
	up_read(&rdev->exclusive_lock);
}