linux-kernel - Re: [PATCH] fbcon: introduce for_each_registered

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Date:   Mon, 2 Jul 2018 09:30:28 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Yisheng Xie <ysxie@...mail.com>, b.zolnierkie@...sung.com,
        keescook@...omium.org, j.w.r.degoede@...il.com,
        david@...hnology.com, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] fbcon: introduce for_each_registered_fb() helper

On Fri, Jun 29, 2018 at 07:20:13PM +0300, Andy Shevchenko wrote:
> On Fri, 2018-06-29 at 00:20 +0800, Yisheng Xie wrote:
> > Following pattern is often used:
> > 
> >  for (i = 0; i < FB_MAX; i++) {
> >         if (registered_fb[i]) {
> >                 ...
> >         }
> >  }
> > 
> > Therefore, as Andy's suggestion, for_each_registered_fb() helper can
> 
> Suggested-by then ?
> 
> > be introduced to make the code easier to read and write by reducing
> > indentation level. It also saves few lines of code in each occurrence.
> > 
> > This patch convert all part here at the same time.
> 
> LGTM except macro implementation. That's why I have mentioned
> for_each_pci_bridge() to look at.
> 
> > +#define for_each_registered_fb(i)		\
> > +	for (i = 0; i < FB_MAX; i++)		\
> > +		if (registered_fb[i])
> > +
> 
> This needs to be protected against nested conditionals.
> Otherwise compiler issues a warning and even may generate wrong code.

See for_each_if() in include/drm/drmP.h ... we should probably lift that
into a general header. The for_each_if() is used all over drm in iterator
macros, exactly to avoid surprises.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch