linux-kernel - Re: [PATCH 18/22] watchdog: mt7621_wdt: Use 'dev' instead of dereferencing it repeatedly

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Message-ID: <20190410195409.GA29802@roeck-us.net>
Date:   Wed, 10 Apr 2019 12:54:09 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Joe Perches <joe@...ches.com>
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org,
        Matthias Brugger <matthias.bgg@...il.com>
Subject: Re: [PATCH 18/22] watchdog: mt7621_wdt: Use 'dev' instead of
 dereferencing it repeatedly

On Wed, Apr 10, 2019 at 11:46:24AM -0700, Joe Perches wrote:
> On Wed, 2019-04-10 at 09:27 -0700, Guenter Roeck wrote:
> > Introduce local variable 'struct device *dev' and use it instead of
> > dereferencing it repeatedly.
> > 
> > The conversion was done automatically with coccinelle using the
> > following semantic patches. The semantic patches and the scripts
> > used to generate this commit log are available at
> > https://github.com/groeck/coccinelle-patches
> 
> Interesting collection.  It would be useful to specify which
> particular script generated or enabled this patch.
> 

It is pdev-addvar.cocci, rule 'new'. deref.cocci wasn't used for the
watchdog patches. The script to apply the various rules is watchdog/make.sh.

Pointing to the actual scripts used is a good idea. I'll see if I can add
this for subsequent series. After all, the commit log is also auto-generated,
so this should be straightforward.

> Just scanning briefly, it might have been this one:
> https://github.com/groeck/coccinelle-patches/blob/master/common/deref.cocci
> But it looks like some manual bit might have been required too.

Not for this one. There were a couple of situations where I had to manually
split long lines to avoid checkpatch warnings, and I manually updated a few
of the commit logs, but not in this patch.

> 
> And trivially:
> 
> > diff --git a/drivers/watchdog/mt7621_wdt.c b/drivers/watchdog/mt7621_wdt.c
> []
> > @@ -133,18 +133,19 @@ static struct watchdog_device mt7621_wdt_dev = {
> []
> >  	watchdog_init_timeout(&mt7621_wdt_dev, mt7621_wdt_dev.max_timeout,
> > -			      &pdev->dev);
> > +			      dev);
> 
> This could be on one line.
> 
Coccinelle isn't perfect. The rule doesn't modify the entire argument list,
only the last argument, so coccinelle missed that it could have merged the
two lines into one.

A checkpatch rule suggesting that multiple extension lines can be merged
might be useful to help finding such situations. Just a thought.

Thanks,
Guenter