linux-kernel - Re: [PATCH 07/15] usb: serial: f81534: use usb_control_msg_recv() and usb_control_msg

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Message-ID: <X8oHrKbjAg3nnJ1n@localhost>
Date:   Fri, 4 Dec 2020 10:55:56 +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 07/15] usb: serial: f81534: use usb_control_msg_recv()
 and usb_control_msg_send()

On Wed, Nov 04, 2020 at 12:16:55PM +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/f81534.c | 63 +++++++++++--------------------------
>  1 file changed, 18 insertions(+), 45 deletions(-)
> 
> diff --git a/drivers/usb/serial/f81534.c b/drivers/usb/serial/f81534.c
> index 5661fd03e545..23eb17a2c052 100644
> --- a/drivers/usb/serial/f81534.c
> +++ b/drivers/usb/serial/f81534.c
> @@ -217,38 +217,26 @@ static int f81534_set_register(struct usb_serial *serial, u16 reg, u8 data)
>  	struct usb_device *dev = serial->dev;
>  	size_t count = F81534_USB_MAX_RETRY;
>  	int status;
> -	u8 *tmp;
> -
> -	tmp = kmalloc(sizeof(u8), GFP_KERNEL);
> -	if (!tmp)
> -		return -ENOMEM;
> -
> -	*tmp = data;
>  
>  	/*
>  	 * Our device maybe not reply when heavily loading, We'll retry for
>  	 * F81534_USB_MAX_RETRY times.
>  	 */
>  	while (count--) {
> -		status = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
> -					 F81534_SET_GET_REGISTER,
> -					 USB_TYPE_VENDOR | USB_DIR_OUT,
> -					 reg, 0, tmp, sizeof(u8),
> -					 F81534_USB_TIMEOUT);
> -		if (status > 0) {
> -			status = 0;
> -			break;
> -		} else if (status == 0) {
> -			status = -EIO;
> +		status = usb_control_msg_send(dev, 0, F81534_SET_GET_REGISTER,
> +					      USB_TYPE_VENDOR | USB_DIR_OUT,
> +					      reg, 0, &data, sizeof(u8),
> +					      F81534_USB_TIMEOUT, GFP_KERNEL);
> +		if (status) {
> +			/* Try again */
> +			continue;
>  		}
>  	}

Here too this change breaks the logic and the control transfer is now
repeated also after successful transfer (ten times!).

This change would also introduce an additional malloc + memcpy for every
retry.

As this is a function that is used often and the comment suggest that
having to retry isn't that rare, I suggest dropping this patch as well.

Johan