[PATCH] asus-laptop: correct error handling in asus_read_brightness()

[PATCH] asus-laptop: correct error handling in asus_read_brightness()

[Giedrius Statkevičius]

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@gmail.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;
+	}
 
 	return value;
 }
-- 
2.8.0

Re: [PATCH] asus-laptop: correct error handling in asus_read_brightness()

[Andy Shevchenko]

On Sat, Apr 16, 2016 at 3:27 AM, Giedrius Statkevičius
<giedrius.statkevicius@gmail.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@gmail.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.

>
>         return value;
>  }
> --
> 2.8.0
>



-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] asus-laptop: correct error handling in asus_read_brightness()

[Giedrius Statkevičius]

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@gmail.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@gmail.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.

Re: [PATCH] asus-laptop: correct error handling in asus_read_brightness()

[Darren Hart]

On Fri, Apr 22, 2016 at 10:43:30AM +0300, Giedrius Statkevičius wrote:
> 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@gmail.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@gmail.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.
> 

As a matter of practice, based on feedback from the previous pdx86 maintainers,
I prefer to accept patches which fix an immediate issue and leave the rework or
broader work as a follow-on, or a TODO item.

We should look for a good place to document these TODOs.

Queued for 4.7.

Thanks,

-- 
Darren Hart
Intel Open Source Technology Center