drm/amdgpu: add debugfs interface for reading MQDs

Provide a debugfs interface to access the MQD.  Useful for
debugging issues with the CP and MES hardware scheduler.

v2: fix missing unreserve/unmap when pos >= size (Alex)

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -509,6 +509,59 @@ static const struct file_operations amdgpu_debugfs_ring_fops = {
 	.llseek = default_llseek
 };
 
+static ssize_t amdgpu_debugfs_mqd_read(struct file *f, char __user *buf,
+				       size_t size, loff_t *pos)
+{
+	struct amdgpu_ring *ring = file_inode(f)->i_private;
+	volatile u32 *mqd;
+	int r;
+	uint32_t value, result;
+
+	if (*pos & 3 || size & 3)
+		return -EINVAL;
+
+	result = 0;
+
+	r = amdgpu_bo_reserve(ring->mqd_obj, false);
+	if (unlikely(r != 0))
+		return r;
+
+	r = amdgpu_bo_kmap(ring->mqd_obj, (void **)&mqd);
+	if (r) {
+		amdgpu_bo_unreserve(ring->mqd_obj);
+		return r;
+	}
+
+	while (size) {
+		if (*pos >= ring->mqd_size)
+			goto done;
+
+		value = mqd[*pos/4];
+		r = put_user(value, (uint32_t *)buf);
+		if (r)
+			goto done;
+		buf += 4;
+		result += 4;
+		size -= 4;
+		*pos += 4;
+	}
+
+done:
+	amdgpu_bo_kunmap(ring->mqd_obj);
+	mqd = NULL;
+	amdgpu_bo_unreserve(ring->mqd_obj);
+	if (r)
+		return r;
+
+	return result;
+}
+
+static const struct file_operations amdgpu_debugfs_mqd_fops = {
+	.owner = THIS_MODULE,
+	.read = amdgpu_debugfs_mqd_read,
+	.llseek = default_llseek
+};
+
 #endif
 
 void amdgpu_debugfs_ring_init(struct amdgpu_device *adev,
@@ -524,6 +577,12 @@ void amdgpu_debugfs_ring_init(struct amdgpu_device *adev,
 				 &amdgpu_debugfs_ring_fops,
 				 ring->ring_size + 12);
 
+	if (ring->mqd_obj) {
+		sprintf(name, "amdgpu_mqd_%s", ring->name);
+		debugfs_create_file_size(name, S_IFREG | S_IRUGO, root, ring,
+					 &amdgpu_debugfs_mqd_fops,
+					 ring->mqd_size);
+	}
 #endif
 }