linux-kernel - Re: [PATCH] xhci: Remove unused value len from xhci_unmap_temp

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Message-ID: <YEd2m3shhzq+Ihh9@kroah.com>
Date:   Tue, 9 Mar 2021 14:22:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Zhangkun <zhangkun4jr@....com>
Cc:     Mathias Nyman <mathias.nyman@...el.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, Zhang Kun <zhangkun@...rlc.com>
Subject: Re: [PATCH] xhci: Remove unused value len from xhci_unmap_temp_buf

On Sun, Mar 07, 2021 at 09:14:26AM +0800, Zhangkun wrote:
> On 3/7/21 12:25 AM, Greg Kroah-Hartman wrote:
> > On Sat, Mar 06, 2021 at 08:06:44PM +0800, zhangkun4jr@....com wrote:
> >> From: Zhang Kun <zhangkun@...rlc.com>
> >>
> >> The value assigned to len by sg_pcopy_from_buffer() never used for
> >> anything, so remove it.
> >>
> >> Signed-off-by: Zhang Kun <zhangkun@...rlc.com>
> >> ---
> >>  drivers/usb/host/xhci.c | 3 +--
> >>  1 file changed, 1 insertion(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> >> index bd27bd670104..6ebda89d476c 100644
> >> --- a/drivers/usb/host/xhci.c
> >> +++ b/drivers/usb/host/xhci.c
> >> @@ -1335,7 +1335,6 @@ static bool xhci_urb_temp_buffer_required(struct usb_hcd *hcd,
> >>  
> >>  static void xhci_unmap_temp_buf(struct usb_hcd *hcd, struct urb *urb)
> >>  {
> >> -	unsigned int len;
> >>  	unsigned int buf_len;
> >>  	enum dma_data_direction dir;
> >>  
> >> @@ -1351,7 +1350,7 @@ static void xhci_unmap_temp_buf(struct usb_hcd *hcd, struct urb *urb)
> >>  				 dir);
> >>  
> >>  	if (usb_urb_dir_in(urb))
> >> -		len = sg_pcopy_from_buffer(urb->sg, urb->num_sgs,
> >> +		sg_pcopy_from_buffer(urb->sg, urb->num_sgs,
> >>  					   urb->transfer_buffer,
> >>  					   buf_len,
> >>  					   0);
> > 
> > SHouldn't this be checked instead of ignored?
> >
> 
> Hi, Greg.
> Considering your tips I checked sg_pcopy_from_buffer(). it copys data
> from urb->transfer_buffer to urb->sg, and only returns 0 or the 
> 'number of copied bytes', and seems to has no other exception branchs
> that need to be checked. So I think it should be ingnored.

Why should you not check that the number of bytes was copied properly?

thanks,

greg k-h