linux-kernel - Re: [PATCH] fbdev: omapfb: panel-sony-acx565akm: Simplify show_cabc_available

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Message-ID: <08fab5a3-4a6c-442c-98f9-672c5afc3609@stanley.mountain>
Date: Fri, 9 Aug 2024 18:13:05 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc: Helge Deller <deller@....de>, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] fbdev: omapfb: panel-sony-acx565akm: Simplify
 show_cabc_available_modes()

On Fri, Aug 09, 2024 at 05:09:28PM +0200, Christophe JAILLET wrote:
> Le 09/08/2024 à 16:42, Dan Carpenter a écrit :
> > On Thu, Aug 08, 2024 at 11:46:11AM +0200, Christophe JAILLET wrote:
> > > Use sysfs_emit_at() instead of snprintf() + custom logic.
> > > Using sysfs_emit_at() is much more simple.
> > > 
> > > Also, sysfs_emit() is already used in this function, so using
> > > sysfs_emit_at() is more consistent.
> > > 
> > > Also simplify the logic:
> > >    - always add a space after an entry
> > >    - change the last space into a '\n'
> > > 
> > > Finally it is easy to see that, given the size of cabc_modes, PAGE_SIZE
> > > can not be reached.
> > > So better keep everything simple (and correct).
> > > 
> > > Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> > > ---
> > >   .../omap2/omapfb/displays/panel-sony-acx565akm.c  | 15 ++++++++-------
> > >   1 file changed, 8 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c b/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
> > > index 71d2e015960c..fc975615d5c9 100644
> > > --- a/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
> > > +++ b/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
> > > @@ -466,19 +466,20 @@ static ssize_t show_cabc_available_modes(struct device *dev,
> > >   		char *buf)
> > >   {
> > >   	struct panel_drv_data *ddata = dev_get_drvdata(dev);
> > > -	int len;
> > > +	int len = 0;
> > >   	int i;
> > >   	if (!ddata->has_cabc)
> > >   		return sysfs_emit(buf, "%s\n", cabc_modes[0]);
> > > -	for (i = 0, len = 0;
> > > -	     len < PAGE_SIZE && i < ARRAY_SIZE(cabc_modes); i++)
> > > -		len += snprintf(&buf[len], PAGE_SIZE - len, "%s%s%s",
> > > -			i ? " " : "", cabc_modes[i],
> > > -			i == ARRAY_SIZE(cabc_modes) - 1 ? "\n" : "");
> > > +	for (i = 0; i < ARRAY_SIZE(cabc_modes); i++)
> > > +		len += sysfs_emit_at(buf, len, "%s ", cabc_modes[i]);
> > > +
> > > +	/* Remove the trailing space */
> > > +	if (len)
> > > +		buf[len - 1] = '\n';
> > 
> > I'm uncomfortable with this line.  It assumes we don't overflow PAGE_SIZE where
> > the original code was careful about checking.  Probably easiest to do what the
> > original code did and say:
> > 
> 
> Hi Dan,
> 
> I don't follow you. AFAIK, it does not assume anything.
> 
> Thanks to sysfs_emit_at(), len can only be in [0..PAGE_SIZE-1] because the
> trailing \0 is not counted.
> 

Ah, you're right.  Sorry for the noise.

regards,
dan carpenter