Re: [PATCH] platform/x86: dell-laptop: Filter out spurious keyboard backlight change events

[Hans de Goede]

Hi,

On 05-01-18 12:07, Pali RohÃr wrote:
> On Friday 05 January 2018 12:40:04 Andy Shevchenko wrote:
> > On Thu, Jan 4, 2018 at 10:52 AM, Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
> > > On some Dell XPS models WMI events of type 0x0000 reporting a keycode of
> > > 0xe00c get reported when the brightness of the LCD panel changes.
> > >
> > > This leads to us reporting false-positive kbd_led change events to
> > > userspace which in turn leads to the kbd backlight OSD showing when it
> > > should not.
> > >
> > > We already read the current keyboard backlight brightness value when
> > > reporting events because the led_classdev_notify_brightness_hw_changed
> > > API requires this. Compare this value to the last known value and filter
> > > out duplicate events, fixing this.
> > >
> > > Note the fixed issue is esp. a problem on XPS models with an ambient light
> > > sensor and automatic brightness adjustments turned on, this causes the kbd
> > > backlight OSD to show all the time there.
> >
> > Should it have Fixes tag?
> >
> > Pali, any comment on this?
>
> See comments below. If there are not any problems, add my:
> Acked-by: Pali RohÃr <pali.rohar@xxxxxxxxx>
>
> > > BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1514969
> > > Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> > > ---
> > >   drivers/platform/x86/dell-laptop.c | 24 ++++++++++++++++++++++--
> > >   1 file changed, 22 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/platform/x86/dell-laptop.c b/drivers/platform/x86/dell-laptop.c
> > > index cd4725e7e0b5..2ef3297a9efc 100644
> > > --- a/drivers/platform/x86/dell-laptop.c
> > > +++ b/drivers/platform/x86/dell-laptop.c
> > > @@ -1133,6 +1133,7 @@ static u8 kbd_previous_mode_bit;
> > >
> > >   static bool kbd_led_present;
> > >   static DEFINE_MUTEX(kbd_led_mutex);
> > > +static enum led_brightness kbd_led_level;
>
> Introduction of cached state of brightness level in kernel driver can
> lead to problem as userspace is able to change brightness (via direct
> DELL SMM API) without notice of kernel.
>
> But now patches for new interaction with DELL SMM via WMI are in kernel
> and there is explicit filter which blocks request for keyboard
> backlight. So hopefully this would not be a problem anymore... (or
> correct me if there still can be).

Right, as discussed previously now that we've kernel support for this
userspace really should not be directly touching this.

> > >   /*
> > >    * NOTE: there are three ways to set the keyboard backlight level.
> > > @@ -1947,6 +1948,7 @@ static enum led_brightness kbd_led_level_get(struct led_classdev *led_cdev)
> > >   static int kbd_led_level_set(struct led_classdev *led_cdev,
> > >                               enum led_brightness value)
> > >   {
> > > +       enum led_brightness new_value = value;
> > >          struct kbd_state state;
> > >          struct kbd_state new_state;
> > >          u16 num;
> > > @@ -1976,6 +1978,9 @@ static int kbd_led_level_set(struct led_classdev *led_cdev,
> > >          }
> > >
> > >   out:
> > > +       if (ret == 0)
> > > +               kbd_led_level = new_value;
> > > +
> > >          mutex_unlock(&kbd_led_mutex);
> > >          return ret;
> > >   }
> > > @@ -2003,6 +2008,9 @@ static int __init kbd_led_init(struct device *dev)
> > >                  if (kbd_led.max_brightness)
> > >                          kbd_led.max_brightness--;
> > >          }
> > > +
> > > +       kbd_led_level = kbd_led_level_get(NULL);
>
> Technically, kbd_led_level_get() is API function for struct led_cdev and
> therefore should take valid kbd_led, NULL there looks suspicious.

Right, but I did not want to pass in a non-registered led_cdev and since
kbd_led_level_get() does not dereference the passed in led_cdev passing
NULL seems the cleanest solution.

> But in
> reality this function itself ignores it first parameter. Probably the
> clean solution would be to have one private function for struct led_cdev
> usage and one which get current level for all other cases. This looks
> ugly too, so if somebody else would not come with better idea, let this
> code as is.

Ack, lets keep this as in, as said it is not perfect but passing NULL
is the cleanest solution.

Regards,

Hans




> > > +
> > >          ret = led_classdev_register(dev, &kbd_led);
> > >          if (ret)
> > >                  kbd_led_present = false;
> > > @@ -2027,13 +2035,25 @@ static void kbd_led_exit(void)
> > >   static int dell_laptop_notifier_call(struct notifier_block *nb,
> > >                                       unsigned long action, void *data)
> > >   {
> > > +       bool changed = false;
> > > +       enum led_brightness new_kbd_led_level;
> > > +
> > >          switch (action) {
> > >          case DELL_LAPTOP_KBD_BACKLIGHT_BRIGHTNESS_CHANGED:
> > >                  if (!kbd_led_present)
> > >                          break;
> > >
> > > -               led_classdev_notify_brightness_hw_changed(&kbd_led,
> > > -                                               kbd_led_level_get(&kbd_led));
> > > +               mutex_lock(&kbd_led_mutex);
> > > +               new_kbd_led_level = kbd_led_level_get(&kbd_led);
> > > +               if (kbd_led_level != new_kbd_led_level) {
> > > +                       kbd_led_level = new_kbd_led_level;
> > > +                       changed = true;
> > > +               }
> > > +               mutex_unlock(&kbd_led_mutex);
> > > +
> > > +               if (changed)
> > > +                       led_classdev_notify_brightness_hw_changed(&kbd_led,
> > > +                                                               kbd_led_level);
> > >                  break;
> > >          }
> > >
> > > --
> > > 2.14.3