整理uvc驱动相关函数的调用流程

1、uvc_video.c

// uvc_video.c
uvc_video_encode_header
uvc_video_encode_data
uvc_video_encode_bulk
uvc_video_encode_isoc
uvcg_video_ep_queue
uvc_video_complete
uvc_video_free_requests  //释放video请求
uvc_video_alloc_requests  //分配video请求
uvcg_video_pump  //Pump video data into the USB requests
uvcg_video_enable  //Enable or disable the video stream
uvcg_video_init  //Initialize UVC video stream

初始化函数的调用关系

uvc_function_bind //f_uvc.c
	uvcg_video_init(&uvc->video, uvc) //f_uvc.c   Initialise video
		uvcg_queue_init  //uvc_video.c Initialize the video buffers queue
			vb2_queue_init // videobuf2-v4l2.c
				vb2_core_queue_init //videobuf2-core.c

2、uvc_queue.c

uvc_queue_setup
uvc_buffer_prepare
uvc_buffer_queue
uvcg_queue_init
uvcg_free_buffers
uvcg_alloc_buffers
uvcg_query_buffer
uvcg_dequeue_buffer
uvcg_queue_poll
uvcg_queue_mmap
uvcg_queue_get_unmapped_area
uvcg_queue_cancel
uvcg_queue_enable
uvcg_queue_next_buffer
uvcg_queue_head

3、uvc_v4l2.c

uvc_send_response
uvc_v4l2_querycap
uvc_v4l2_get_format
uvc_v4l2_set_format
uvc_v4l2_reqbufs
uvc_v4l2_querybuf
uvc_v4l2_qbuf
uvc_v4l2_dqbuf
uvc_v4l2_streamon
uvc_v4l2_streamoff
uvc_v4l2_subscribe_event
uvc_v4l2_unsubscribe_event
uvc_v4l2_extend_configuration
uvc_v4l2_ioctl_default
uvc_v4l2_open
uvc_v4l2_release
uvc_v4l2_mmap
uvc_v4l2_poll
uvcg_v4l2_get_unmapped_area

#define call_qop(q, op, args...)					\
({									\
	int err;							\
									\
	log_qop(q, op);							\
	err = (q)->ops->op ? (q)->ops->op(args) : 0;			\
	if (!err)							\
		(q)->cnt_ ## op++;					\
	err;								\
})

uvc_function_bind //f_uvc.c
	uvc_register_video //f_uvc.c 
		结构体uvc_v4l2_ioctl_ops  //uvc_v4l2.c
			uvc_v4l2_streamon  //uvc_v4l2.c
				uvcg_video_enable  //uvc_video.c
					uvcg_queue_enable  //uvc_queue.c
						vb2_streamon //videobuf2-v4l2.c
							vb2_core_streamon //videobuf2-core.c
								vb2_start_streaming //videobuf2-core.c
									call_qop(q, start_streaming, q,atomic_read(&q->owned_by_drv_count)) videobuf2-core.c
	

4、v4l2-core

参考文章：https://blog.csdn.net/u013836909/article/details/125360024

//drivers\media\v4l2-core\v4l2-dev.c
static const struct file_operations v4l2_fops = {
	.owner = THIS_MODULE,
	.read = v4l2_read,
	.write = v4l2_write,
	.open = v4l2_open,
	.get_unmapped_area = v4l2_get_unmapped_area,
	.mmap = v4l2_mmap,
	.unlocked_ioctl = v4l2_ioctl,
#ifdef CONFIG_COMPAT
	.compat_ioctl = v4l2_compat_ioctl32,
#endif
	.release = v4l2_release,
	.poll = v4l2_poll,
	.llseek = no_llseek,
};

video_register_device //include/media/v4l2-dev.h
	__video_register_device //drivers/media/v4l2-core/v4l2-dev.c
		//自动创建设备节点
		device_register //drivers/media/v4l2-core/v4l2-dev.c	

// include\media\v4l2-dev.h
/**
 * struct v4l2_file_operations - fs operations used by a V4L2 device
 *
 * @owner: pointer to struct module
 * @read: operations needed to implement the read() syscall
 * @write: operations needed to implement the write() syscall
 * @poll: operations needed to implement the poll() syscall
 * @unlocked_ioctl: operations needed to implement the ioctl() syscall
 * @compat_ioctl32: operations needed to implement the ioctl() syscall for
 *	the special case where the Kernel uses 64 bits instructions, but
 *	the userspace uses 32 bits.
 * @get_unmapped_area: called by the mmap() syscall, used when %!CONFIG_MMU
 * @mmap: operations needed to implement the mmap() syscall
 * @open: operations needed to implement the open() syscall
 * @release: operations needed to implement the release() syscall
 *
 * .. note::
 *
 *	Those operations are used to implemente the fs struct file_operations
 *	at the V4L2 drivers. The V4L2 core overrides the fs ops with some
 *	extra logic needed by the subsystem.
 */
struct v4l2_file_operations {
	struct module *owner;
	ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
	__poll_t (*poll) (struct file *, struct poll_table_struct *);
	long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
#ifdef CONFIG_COMPAT
	long (*compat_ioctl32) (struct file *, unsigned int, unsigned long);
#endif
	unsigned long (*get_unmapped_area) (struct file *, unsigned long,
				unsigned long, unsigned long, unsigned long);
	int (*mmap) (struct file *, struct vm_area_struct *);
	int (*open) (struct file *);
	int (*release) (struct file *);
};

static const struct file_operations v4l2_fops = {
	.owner = THIS_MODULE,
	.read = v4l2_read,
	.write = v4l2_write,
	.open = v4l2_open,
	.get_unmapped_area = v4l2_get_unmapped_area,
	.mmap = v4l2_mmap,
	.unlocked_ioctl = v4l2_ioctl,
#ifdef CONFIG_COMPAT
	.compat_ioctl = v4l2_compat_ioctl32,
#endif
	.release = v4l2_release,
	.poll = v4l2_poll,
	.llseek = no_llseek,
};

通过V4L2子系统提供的v4l2_fops集合，可直接调用底层驱动实现的Video主设备struct v4l2_file_operations方法

__video_register_device
	vdev->cdev->ops = &v4l2_fops
		v4l2_open
			vdev->fops->open(filp) //调用uvc_v4l2.c中的uvc_v4l2_open		
		v4l2_ioctl
			vdev->fops->unlocked_ioctl(filp, cmd, arg) //调用uvc_v4l2.c中的video_ioctl2
				video_usercopy(file, cmd, arg, __video_do_ioctl)
					回调__video_do_ioctl		
						ops->vidioc_default //调用uvc_v4l2.c中的vidioc_default

//drivers\media\v4l2-core\v4l2-ioctl.c
long video_ioctl2(struct file *file,
	       unsigned int cmd, unsigned long arg)
{
	return video_usercopy(file, cmd, arg, __video_do_ioctl);
}
EXPORT_SYMBOL(video_ioctl2);

5、数据传输

参考文章：https://blog.csdn.net/qq_32938605/article/details/119787380

1、分配一个gadget请求

// \udc\ambarella_udc.c
static const struct usb_ep_ops ambarella_ep_ops = {
	.enable		= ambarella_udc_ep_enable,
	.disable	= ambarella_udc_ep_disable,

	.alloc_request	= ambarella_udc_alloc_request,
	.free_request	= ambarella_udc_free_request,

	.queue		= ambarella_udc_queue,
	.dequeue	= ambarella_udc_dequeue,

	.set_halt	= ambarella_udc_set_halt,
	/* fifo ops not implemented */
};

usb_ep_alloc_request 分配一个gadget请求

// \udc\core.c
/**
 * usb_ep_alloc_request - allocate a request object to use with this endpoint
 * @ep:the endpoint to be used with with the request
 * @gfp_flags:GFP_* flags to use
 *
 * Request objects must be allocated with this call, since they normally
 * need controller-specific setup and may even need endpoint-specific
 * resources such as allocation of DMA descriptors.
 * Requests may be submitted with usb_ep_queue(), and receive a single
 * completion callback.  Free requests with usb_ep_free_request(), when
 * they are no longer needed.
 *
 * Returns the request, or null if one could not be allocated.
 */
struct usb_request *usb_ep_alloc_request(struct usb_ep *ep,
						       gfp_t gfp_flags)
{
	struct usb_request *req = NULL;

	req = ep->ops->alloc_request(ep, gfp_flags);

	trace_usb_ep_alloc_request(ep, req, req ? 0 : -ENOMEM);

	return req;
}
EXPORT_SYMBOL_GPL(usb_ep_alloc_request);

//f_uvc.c的bind()函数
/* Preallocate control endpoint request. */
	uvc->control_req = usb_ep_alloc_request(cdev->gadget->ep0, GFP_KERNEL);
	uvc->control_buf = kmalloc(UVC_MAX_REQUEST_SIZE, GFP_KERNEL);
	if (uvc->control_req == NULL || uvc->control_buf == NULL) {
		ret = -ENOMEM;
		goto error;
	}

	uvc->control_req->buf = uvc->control_buf;
	uvc->control_req->complete = uvc_function_ep0_complete;
	uvc->control_req->context = uvc;

 //ambarella_udc.c
ambarella_udc_probe
	ambarella_init_gadget
		ep->ep.ops = &ambarella_ep_ops

2、请求一个queue

usb_ep_queue 请求一个queue

/**
 * usb_ep_queue - queues (submits) an I/O request to an endpoint.
 * @ep:the endpoint associated with the request
 * @req:the request being submitted
 * @gfp_flags: GFP_* flags to use in case the lower level driver couldn't
 *	pre-allocate all necessary memory with the request.
 *
 * This tells the device controller to perform the specified request through
 * that endpoint (reading or writing a buffer).  When the request completes,
 * including being canceled by usb_ep_dequeue(), the request's completion
 * routine is called to return the request to the driver.  Any endpoint
 * (except control endpoints like ep0) may have more than one transfer
 * request queued; they complete in FIFO order.  Once a gadget driver
 * submits a request, that request may not be examined or modified until it
 * is given back to that driver through the completion callback.
 *
 * Each request is turned into one or more packets.  The controller driver
 * never merges adjacent requests into the same packet.  OUT transfers
 * will sometimes use data that's already buffered in the hardware.
 * Drivers can rely on the fact that the first byte of the request's buffer
 * always corresponds to the first byte of some USB packet, for both
 * IN and OUT transfers.
 *
 * Bulk endpoints can queue any amount of data; the transfer is packetized
 * automatically.  The last packet will be short if the request doesn't fill it
 * out completely.  Zero length packets (ZLPs) should be avoided in portable
 * protocols since not all usb hardware can successfully handle zero length
 * packets.  (ZLPs may be explicitly written, and may be implicitly written if
 * the request 'zero' flag is set.)  Bulk endpoints may also be used
 * for interrupt transfers; but the reverse is not true, and some endpoints
 * won't support every interrupt transfer.  (Such as 768 byte packets.)
 *
 * Interrupt-only endpoints are less functional than bulk endpoints, for
 * example by not supporting queueing or not handling buffers that are
 * larger than the endpoint's maxpacket size.  They may also treat data
 * toggle differently.
 *
 * Control endpoints ... after getting a setup() callback, the driver queues
 * one response (even if it would be zero length).  That enables the
 * status ack, after transferring data as specified in the response.  Setup
 * functions may return negative error codes to generate protocol stalls.
 * (Note that some USB device controllers disallow protocol stall responses
 * in some cases.)  When control responses are deferred (the response is
 * written after the setup callback returns), then usb_ep_set_halt() may be
 * used on ep0 to trigger protocol stalls.  Depending on the controller,
 * it may not be possible to trigger a status-stage protocol stall when the
 * data stage is over, that is, from within the response's completion
 * routine.
 *
 * For periodic endpoints, like interrupt or isochronous ones, the usb host
 * arranges to poll once per interval, and the gadget driver usually will
 * have queued some data to transfer at that time.
 *
 * Note that @req's ->complete() callback must never be called from
 * within usb_ep_queue() as that can create deadlock situations.
 *
 * This routine may be called in interrupt context.
 *
 * Returns zero, or a negative error code.  Endpoints that are not enabled
 * report errors; errors will also be
 * reported when the usb peripheral is disconnected.
 *
 * If and only if @req is successfully queued (the return value is zero),
 * @req->complete() will be called exactly once, when the Gadget core and
 * UDC are finished with the request.  When the completion function is called,
 * control of the request is returned to the device driver which submitted it.
 * The completion handler may then immediately free or reuse @req.
 */
int usb_ep_queue(struct usb_ep *ep,
			       struct usb_request *req, gfp_t gfp_flags)
{
	int ret = 0;

	if (WARN_ON_ONCE(!ep->enabled && ep->address)) {
		ret = -ESHUTDOWN;
		goto out;
	}

	ret = ep->ops->queue(ep, req, gfp_flags);

out:
	trace_usb_ep_queue(ep, req, ret);

	return ret;
}
EXPORT_SYMBOL_GPL(usb_ep_queue);

usb_ep_queue的调用流程

// uvc_v4l2.c
ioctl(dev->fd, UVCIOC_SEND_RESPONSE, &resp)//应用层
uvc_v4l2_ioctl_default
	uvc_send_response(uvc, arg)
		usb_ep_queue(cdev->gadget->ep0, req, GFP_KERNEL)