linux-kernel - Re: [PATCH 01/15] usb: serial: ark3116: use usb_control_msg_recv() and usb_control_msg

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Date:   Fri, 4 Dec 2020 10:16:07 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Himadri Pandya <himadrispandya@...il.com>
Cc:     johan@...nel.org, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH 01/15] usb: serial: ark3116: use usb_control_msg_recv()
 and usb_control_msg_send()

On Wed, Nov 04, 2020 at 12:16:49PM +0530, Himadri Pandya wrote:
> The new usb_control_msg_recv() and usb_control_msg_send() nicely wraps
> usb_control_msg() with proper error check. Hence use the wrappers
> instead of calling usb_control_msg() directly.
> 
> Signed-off-by: Himadri Pandya <himadrispandya@...il.com>
> ---
>  drivers/usb/serial/ark3116.c | 29 ++++-------------------------
>  1 file changed, 4 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/usb/serial/ark3116.c b/drivers/usb/serial/ark3116.c
> index 71a9206ea1e2..51302892c779 100644
> --- a/drivers/usb/serial/ark3116.c
> +++ b/drivers/usb/serial/ark3116.c
> @@ -77,38 +77,17 @@ struct ark3116_private {
>  static int ark3116_write_reg(struct usb_serial *serial,
>  			     unsigned reg, __u8 val)
>  {
> -	int result;
>  	 /* 0xfe 0x40 are magic values taken from original driver */
> -	result = usb_control_msg(serial->dev,
> -				 usb_sndctrlpipe(serial->dev, 0),
> -				 0xfe, 0x40, val, reg,
> -				 NULL, 0, ARK_TIMEOUT);
> -	if (result)
> -		return result;
> -
> -	return 0;
> +	return usb_control_msg_send(serial->dev, 0, 0xfe, 0x40, val, reg, NULL, 0,
> +				    ARK_TIMEOUT, GFP_KERNEL);

For control transfers without a data stage there's no point in using
usb_control_msg_send() as it already returns a negative errno on error
or 0 on success.

>  }
>  
>  static int ark3116_read_reg(struct usb_serial *serial,
>  			    unsigned reg, unsigned char *buf)
>  {
> -	int result;
>  	/* 0xfe 0xc0 are magic values taken from original driver */
> -	result = usb_control_msg(serial->dev,
> -				 usb_rcvctrlpipe(serial->dev, 0),
> -				 0xfe, 0xc0, 0, reg,
> -				 buf, 1, ARK_TIMEOUT);
> -	if (result < 1) {
> -		dev_err(&serial->interface->dev,
> -				"failed to read register %u: %d\n",
> -				reg, result);
> -		if (result >= 0)
> -			result = -EIO;
> -
> -		return result;
> -	}
> -
> -	return 0;
> +	return usb_control_msg_recv(serial->dev, 0, 0xfe, 0xc0, 0, reg, buf, 1,
> +				    ARK_TIMEOUT, GFP_KERNEL);

This driver already use a DMA-able transfer buffer which is allocated
once and then passed to this helper repeatedly. This change would
introduce additional redandant memdup + memcpy for every call and for no
real gain.

You also have an unrelated change here as you simply remove an existing
error message.

Please drop this patch.

Johan