linux-kernel - Re: [PATCH] Input: atmel_mxt_ts - Remove unnecessary byte

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Date:   Mon, 9 Oct 2017 22:06:53 +0100
From:   Christos Gkekas <chris.gekas@...il.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Nick Dyer <nick@...anahar.org>, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Input: atmel_mxt_ts - Remove unnecessary byte_offset
 check

On 09/10/17 10:38:55 -0700, Dmitry Torokhov wrote:
> On Sun, Oct 08, 2017 at 08:41:16PM +0100, Nick Dyer wrote:
> > On Sun, Oct 08, 2017 at 07:44:18PM +0100, Christos Gkekas wrote:
> > > Variable byte_offset is unsigned so checking whether it is greater or
> > > equal to zero is redundant.
> > > 
> > > Signed-off-by: Christos Gkekas <chris.gekas@...il.com>
> > 
> > Yep - looks sensible to me.
> > 
> > Signed-off-by: Nick Dyer <nick@...anahar.org>
> 
> I believe this has been discussed before and Linus told us to keep the
> such checks as is: they neatly document the ranges of values, safe in
> case we ever change the type of the variables, and do not cost us
> anything at execution time.
> 

Fair enough, thanks for your feedback.

I believe you are referring to this:
https://lkml.org/lkml/2006/11/28/206

Regards,
Christos

> 
> > 
> > > ---
> > >  drivers/input/touchscreen/atmel_mxt_ts.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c b/drivers/input/touchscreen/atmel_mxt_ts.c
> > > index 7659bc4..baafaed 100644
> > > --- a/drivers/input/touchscreen/atmel_mxt_ts.c
> > > +++ b/drivers/input/touchscreen/atmel_mxt_ts.c
> > > @@ -1356,7 +1356,7 @@ static int mxt_prepare_cfg_mem(struct mxt_data *data,
> > >  
> > >  			byte_offset = reg + i - cfg_start_ofs;
> > >  
> > > -			if (byte_offset >= 0 && byte_offset < config_mem_size) {
> > > +			if (byte_offset < config_mem_size) {
> > >  				*(config_mem + byte_offset) = val;
> > >  			} else {
> > >  				dev_err(dev, "Bad object: reg:%d, T%d, ofs=%d\n",
> > > -- 
> > > 2.7.4
> > > 
> 
> Thanks.
> 
> -- 
> Dmitry