linux-kernel - Re: [PATCH] asus-laptop: correct error handling in asus_read

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Date:	Fri, 22 Apr 2016 10:43:30 +0300
From:	Giedrius Statkevičius 
	<giedrius.statkevicius@...il.com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	Corentin Chary <corentin.chary@...il.com>,
	"dvhart@...radead.org" <dvhart@...radead.org>,
	acpi4asus-user@...ts.sourceforge.net,
	platform-driver-x86@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] asus-laptop: correct error handling in
 asus_read_brightness()

On Fri, Apr 22, 2016 at 02:09:22AM +0300, Andy Shevchenko wrote:
> On Sat, Apr 16, 2016 at 3:27 AM, Giedrius Statkevičius
> <giedrius.statkevicius@...il.com> wrote:
> > It is possible that acpi_evaluate_integer might fail and value would not be
> > set to any value so correct this defect by returning 0 in case of an
> > error. This is also the correct thing to return because the backlight
> > subsystem will print the old value of brightness in this case.
> >
> > Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@...il.com>
> > ---
> >  drivers/platform/x86/asus-laptop.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/platform/x86/asus-laptop.c b/drivers/platform/x86/asus-laptop.c
> > index 9a69734..15f1311 100644
> > --- a/drivers/platform/x86/asus-laptop.c
> > +++ b/drivers/platform/x86/asus-laptop.c
> > @@ -775,8 +775,10 @@ static int asus_read_brightness(struct backlight_device *bd)
> >
> >         rv = acpi_evaluate_integer(asus->handle, METHOD_BRIGHTNESS_GET,
> >                                    NULL, &value);
> > -       if (ACPI_FAILURE(rv))
> > +       if (ACPI_FAILURE(rv)) {
> >                 pr_warn("Error reading brightness\n");
> > +               return 0;
> > +       }
> 
> This looks like a workaround.
> I suppose the real fix is to return here an error code and fix all callers, like
> drivers/video/backlight/backlight.c.
> 

It just fixes the behaviour according to the current code in that file. I
suppose that would be nice but I don't think it would make any difference
because the backlight core code still prints out ->props.brightness in case
ops->get_brightness fails. Just the difference would be that now actual error
messages are printed in the drivers themselves instead of generic messages from
the backlight core. Anyway, I think the current behaviour is more useful because
the drivers know better about what has failed.