linux-kernel - Re: [PATCH -next] usb: ftdi-elan: Fix if == else warnings in ftdi_elan_respond

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Message-ID: <20190123134147.GC24700@kroah.com>
Date:   Wed, 23 Jan 2019 14:41:48 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     YueHaibing <yuehaibing@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH -next] usb: ftdi-elan: Fix if == else warnings in
 ftdi_elan_respond_engine

On Wed, Jan 23, 2019 at 09:17:38PM +0800, YueHaibing wrote:
> On 2019/1/23 20:43, Greg KH wrote:
> > On Wed, Jan 23, 2019 at 08:34:42PM +0800, YueHaibing wrote:
> >> ./drivers/usb/misc/ftdi-elan.c:972:10-12: WARNING: possible condition with no effect (if == else)
> >> ./drivers/usb/misc/ftdi-elan.c:983:9-11: WARNING: possible condition with no effect (if == else)
> >> ./drivers/usb/misc/ftdi-elan.c:2052:11-13: WARNING: possible condition with no effect (if == else)
> >>
> >> Signed-off-by: YueHaibing <yuehaibing@...wei.com>
> > 
> > You can not just provide the output of a tool as a changelog text,
> > sorry.
> > 
> > Please explain what those lines mean, and why you are making the change
> > that you are.
> 
> ok, will do that.
> 
> > 
> >> ---
> >>  drivers/usb/misc/ftdi-elan.c | 26 --------------------------
> >>  1 file changed, 26 deletions(-)
> >>
> >> diff --git a/drivers/usb/misc/ftdi-elan.c b/drivers/usb/misc/ftdi-elan.c
> >> index 76c718a..257efac 100644
> >> --- a/drivers/usb/misc/ftdi-elan.c
> >> +++ b/drivers/usb/misc/ftdi-elan.c
> >> @@ -915,7 +915,6 @@ static int ftdi_elan_respond_engine(struct usb_ftdi *ftdi)
> >>  	int bytes_read = 0;
> >>  	int retry_on_empty = 1;
> >>  	int retry_on_timeout = 3;
> >> -	int empty_packets = 0;
> >>  read:{
> >>  		int packet_bytes = 0;
> >>  		int retval = usb_bulk_msg(ftdi->udev,
> >> @@ -960,31 +959,6 @@ read:{
> >>  			dev_err(&ftdi->udev->dev, "error = %d with packet_bytes = %d with total %d bytes%s\n",
> >>  				retval, packet_bytes, bytes_read, diag);
> >>  			return retval;
> >> -		} else if (packet_bytes == 2) {
> >> -			unsigned char s0 = ftdi->bulk_in_buffer[0];
> >> -			unsigned char s1 = ftdi->bulk_in_buffer[1];
> >> -			empty_packets += 1;
> >> -			if (s0 == 0x31 && s1 == 0x60) {
> >> -				if (retry_on_empty-- > 0) {
> >> -					goto more;
> >> -				} else
> >> -					return 0;
> >> -			} else if (s0 == 0x31 && s1 == 0x00) {
> >> -				if (retry_on_empty-- > 0) {
> >> -					goto more;
> >> -				} else
> >> -					return 0;
> >> -			} else {
> >> -				if (retry_on_empty-- > 0) {
> >> -					goto more;
> >> -				} else
> >> -					return 0;
> >> -			}
> >> -		} else if (packet_bytes == 1) {
> >> -			if (retry_on_empty-- > 0) {
> >> -				goto more;
> >> -			} else
> >> -				return 0;
> > 
> > Are you _sure_ that these lines are not needed and that the compiler is
> > not really seeing them?  As it doesn't look that way to me, what am I
> > missing?
> 
> I checked and make sure that All these if/else if branch just do the same thing:
> 
> 	if (retry_on_empty-- > 0) {
> 		goto more;
> 	} else
> 		return 0;
> 
> so it can be merged into the last else branch.
> 
> Also the variable 'empty_packets' doesn't use in any place, except for self increment

Don't do two different things in the same patch :)