Re: [PATCH v2 2/6] USB: serial: cp210x: use usb_control_msg_recv() and usb_control_msg_send()

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On Mon, Aug 02, 2021 at 02:01:18AM +0530, Himadri Pandya wrote:
> The new wrapper functions for usb_control_msg() can accept data from
> stack with robust error checks.

Please rephrase the "robust error checks" along the lines of "treats
short reads as an error".

> Hence use the wrappers with stack
> variables for usb transfer buffers to save kernel memory.

Again, you're not saving memory here, just moving the allocation.

> Signed-off-by: Himadri Pandya <himadrispandya@xxxxxxxxx>
> ---
> Changes in v2:
>  - Drop unrelated style fixes
> ---
>  drivers/usb/serial/cp210x.c | 107 ++++++++++--------------------------
>  1 file changed, 30 insertions(+), 77 deletions(-)
> 
> diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
> index 3c80bfbf3bec..b73581fc1768 100644
> --- a/drivers/usb/serial/cp210x.c
> +++ b/drivers/usb/serial/cp210x.c
> @@ -628,29 +628,18 @@ static int cp210x_read_reg_block(struct usb_serial_port *port, u8 req,
>  {
>  	struct usb_serial *serial = port->serial;
>  	struct cp210x_port_private *port_priv = usb_get_serial_port_data(port);
> -	void *dmabuf;
>  	int result;
>  
> -	dmabuf = kmalloc(bufsize, GFP_KERNEL);
> -	if (!dmabuf)
> -		return -ENOMEM;
> -
> -	result = usb_control_msg(serial->dev, usb_rcvctrlpipe(serial->dev, 0),
> -			req, REQTYPE_INTERFACE_TO_HOST, 0,
> -			port_priv->bInterfaceNumber, dmabuf, bufsize,
> -			USB_CTRL_SET_TIMEOUT);
> -	if (result == bufsize) {
> -		memcpy(buf, dmabuf, bufsize);
> -		result = 0;
> -	} else {
> +	result = usb_control_msg_recv(serial->dev, 0, req,
> +				      REQTYPE_INTERFACE_TO_HOST, 0,
> +				      port_priv->bInterfaceNumber, buf,
> +				      bufsize, USB_CTRL_SET_TIMEOUT,
> +				      GFP_KERNEL);
> +	if (result) {
>  		dev_err(&port->dev, "failed get req 0x%x size %d status: %d\n",
>  				req, bufsize, result);

This will also no longer log the length of short reads. Please at least
mention it in the commit message.

> -		if (result >= 0)
> -			result = -EIO;
>  	}
>  
> -	kfree(dmabuf);
> -
>  	return result;
>  }

Johan



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