linux-kernel - Re: [PATCH] usb: host: Use helper function to get endpoint

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Message-ID: <YwY4cVdB3tVVMIqJ@rowland.harvard.edu>
Date:   Wed, 24 Aug 2022 10:40:49 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Khalid Masum <khalid.masum.92@...il.com>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Arnd Bergmann <arnd@...db.de>,
        Matthias Kaehlcke <mka@...omium.org>,
        Alexey Sheplyakov <asheplyakov@...ealt.ru>,
        Weitao Wang <WeitaoWang-oc@...oxin.com>,
        linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] usb: host: Use helper function to get endpoint

On Wed, Aug 24, 2022 at 07:07:02PM +0600, Khalid Masum wrote:
> Current implementation to convert urb pipe number to struct 
> usb_host_endpoint in rquest_single_step_set_feature_urb is a little
> messy. 
> 
> Use usb_pipe_endpoint helper function to get the endpoint instead.
> 
> Signed-off-by: Khalid Masum <khalid.masum.92@...il.com>
> ---
>  drivers/usb/core/hcd.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index 94b305bbd621..107e29d5d3ae 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -2165,8 +2165,7 @@ static struct urb *request_single_step_set_feature_urb(
>  		return NULL;
>  
>  	urb->pipe = usb_rcvctrlpipe(udev, 0);
> -	ep = (usb_pipein(urb->pipe) ? udev->ep_in : udev->ep_out)
> -				[usb_pipeendpoint(urb->pipe)];
> +	ep = usb_pipe_endpoint(udev, urb->pipe);
>  	if (!ep) {
>  		usb_free_urb(urb);
>  		return NULL;

Even this is awkward.  It's silly to look up the endpoint in a table 
when you already know that it is endpoint 0.  Just do:

	ep = &udev->ep0;

with no need to check for NULL.

Alan Stern