Re: [PATCH] usb: add flow control to u_serial

[Sascha Hauer <s.hauer@pengutronix.de>]

On Fri, Oct 26, 2012 at 08:37:21PM +0200, Robert Jarzmik wrote:
> When using the serial console over USB to download files, and
> when the USB bandwidth is pushed to its limits, the barebox UDC
> device won't be able to absorb all the traffic.
> 
> Modify the u_serial gadget so that if there is not enough room
> in buffers, don't push USB requests down the gadget driver, so
> that it is saturated, and give it a chance to NAK requests.
> 
> The previous behaviour was loosing bytes (as kfifo_put is lossy).
> The fixed behavious is lossless (based on USB NAK protocol).
> 
> While at it, increase a bit buffer sizes to 8kB to absorb heavy
> transfers such as a linux kernel image.
> 
> Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>

Applied, thanks

Sascha

> ---
>  drivers/usb/gadget/u_serial.c |   25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/usb/gadget/u_serial.c b/drivers/usb/gadget/u_serial.c
> index 946b4f2..162439e 100644
> --- a/drivers/usb/gadget/u_serial.c
> +++ b/drivers/usb/gadget/u_serial.c
> @@ -74,9 +74,9 @@
>   * next layer of buffering.  For TX that's a circular buffer; for RX
>   * consider it a NOP.  A third layer is provided by the TTY code.
>   */
> -#define QUEUE_SIZE		16
> +#define QUEUE_SIZE		128
>  #define WRITE_BUF_SIZE		8192		/* TX only */
> -
> +#define RECV_FIFO_SIZE		(1024 * 8)
>  /*
>   * The port structure holds info for each port, one for each minor number
>   * (and thus for each /dev/ node).
> @@ -92,7 +92,7 @@ struct gs_port {
>  	u8			port_num;
>  
>  	struct list_head	read_pool;
> -	unsigned		n_read;
> +	unsigned		read_nb_queued;
>  
>  	struct list_head	write_pool;
>  
> @@ -123,7 +123,9 @@ static unsigned gs_start_rx(struct gs_port *port)
>  	struct usb_ep		*out = port->port_usb->out;
>  	unsigned		started = 0;
>  
> -	while (!list_empty(pool)) {
> +	while (!list_empty(pool) &&
> +	       ((out->maxpacket * (port->read_nb_queued + 1) +
> +		kfifo_len(port->recv_fifo)) < RECV_FIFO_SIZE)) {
>  		struct usb_request	*req;
>  		int			status;
>  
> @@ -134,6 +136,7 @@ static unsigned gs_start_rx(struct gs_port *port)
>  		/* drop lock while we call out; the controller driver
>  		 * may need to call us back (e.g. for disconnect)
>  		 */
> +		port->read_nb_queued++;
>  		status = usb_ep_queue(out, req);
>  
>  		if (status) {
> @@ -161,8 +164,9 @@ static void gs_read_complete(struct usb_ep *ep, struct usb_request *req)
>  		return;
>  
>  	kfifo_put(port->recv_fifo, req->buf, req->actual);
> -
>  	list_add_tail(&req->list, &port->read_pool);
> +	port->read_nb_queued--;
> +
>  	gs_start_rx(port);
>  }
>  
> @@ -276,7 +280,7 @@ static int gs_start_io(struct gs_port *port)
>  	}
>  
>  	/* queue read requests */
> -	port->n_read = 0;
> +	port->read_nb_queued = 0;
>  	started = gs_start_rx(port);
>  
>  	/* unblock any pending writes into our circular buffer */
> @@ -396,6 +400,7 @@ static int serial_tstc(struct console_device *cdev)
>  	struct gs_port	*port = container_of(cdev,
>  					struct gs_port, cdev);
>  
> +	gs_start_rx(port);
>  	return (kfifo_len(port->recv_fifo) == 0) ? 0 : 1;
>  }
>  
> @@ -412,10 +417,14 @@ static int serial_getc(struct console_device *cdev)
>  	while (kfifo_getc(port->recv_fifo, &ch)) {
>  		usb_gadget_poll();
>  		if (is_timeout(to, 300 * MSECOND))
> -			break;
> +			goto timeout;
>  	}
>  
> +	gs_start_rx(port);
>  	return ch;
> +timeout:
> +	gs_start_rx(port);
> +	return -ETIMEDOUT;
>  }
>  
>  static void serial_flush(struct console_device *cdev)
> @@ -461,7 +470,7 @@ int gserial_connect(struct gserial *gser, u8 port_num)
>  	 */
>  	gser->port_line_coding = port->port_line_coding;
>  
> -	port->recv_fifo = kfifo_alloc(1024);
> +	port->recv_fifo = kfifo_alloc(RECV_FIFO_SIZE);
>  
>  	/*printf("gserial_connect: start ttyGS%d\n", port->port_num);*/
>  	gs_start_io(port);
> -- 
> 1.7.10
> 
> 
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