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

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Date:   Wed, 23 Jan 2019 21:17:38 +0800
From:   YueHaibing <yuehaibing@...wei.com>
To:     Greg KH <gregkh@...uxfoundation.org>
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 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

> 
> thanks,
> 
> greg k-h
> 
> .
>