[v2] gpiolib: notify user-space about line state changes triggered by kernel

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

We currently only emit CHANGED_CONFIG events when the user-space changes
GPIO config. We won't be notified if changes come from in-kernel. Let's
call the notifier chain whenever kernel users change direction or any of
the active-low, debounce or consumer name settings. We don't notify the
user-space about the persistence as the uAPI has no notion of it.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
v1 -> v2:
- use the gpiod_line_state_notify() helper
- reorder the code in gpiod_set_debounce() for better readability

 drivers/gpio/gpiolib.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

On Thu, Aug 24, 2023 at 11:08 AM Kent Gibson <warthog618@gmail.com> wrote:
>
> On Thu, Aug 24, 2023 at 10:55:44AM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> >
> > We currently only emit CHANGED_CONFIG events when the user-space changes
> > GPIO config. We won't be notified if changes come from in-kernel. Let's
> > call the notifier chain whenever kernel users change direction or any of
> > the active-low, debounce or consumer name settings. We don't notify the
> > user-space about the persistence as the uAPI has no notion of it.
> >
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> > ---
> > v1 -> v2:
> > - use the gpiod_line_state_notify() helper
> > - reorder the code in gpiod_set_debounce() for better readability
> >
> >  drivers/gpio/gpiolib.c | 16 ++++++++++++++--
> >  1 file changed, 14 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index 40a0022ea719..1cb7731550ca 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -2439,6 +2439,7 @@ int gpiod_direction_input(struct gpio_desc *desc)
> >       }
> >       if (ret == 0) {
> >               clear_bit(FLAG_IS_OUT, &desc->flags);
> > +             gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
> >               ret = gpio_set_bias(desc);
> >       }
> >
>
> gpiod_direction_input() is called by cdev when a line is requested.
> So requesting a line now creates two events - REQUESTED and
> HANGED_CONFIG? Even worse - it calls gpiod_direction_input() first, so we
> will get CHANGED_CONFIG then REQUESTED??
>
> And a config change from cdev can call this and then generate a
> CHANGED_CONFIG event itself, so again double events.
>
> Same for output and probably debounce too (that one is a bit more
> convoluted).

Ah, should have tested it with user-space too...

Back to the drawing board I guess. May be the reason why we're not
doing it in the first place yet.

Bart

>
> Cheers,
> Kent.
>
> > @@ -2484,8 +2485,10 @@ static int gpiod_direction_output_raw_commit(struct gpio_desc *desc, int value)
> >               gc->set(gc, gpio_chip_hwgpio(desc), val);
> >       }
> >
> > -     if (!ret)
> > +     if (!ret) {
> >               set_bit(FLAG_IS_OUT, &desc->flags);
> > +             gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
> > +     }
> >       trace_gpio_value(desc_to_gpio(desc), 0, val);
> >       trace_gpio_direction(desc_to_gpio(desc), 0, ret);
> >       return ret;
> > @@ -2672,9 +2675,16 @@ EXPORT_SYMBOL_GPL(gpiod_set_config);
> >  int gpiod_set_debounce(struct gpio_desc *desc, unsigned int debounce)
> >  {
> >       unsigned long config;
> > +     int ret;
> >
> >       config = pinconf_to_config_packed(PIN_CONFIG_INPUT_DEBOUNCE, debounce);
> > -     return gpiod_set_config(desc, config);
> > +     ret = gpiod_set_config(desc, config);
> > +     if (ret)
> > +             return ret;
> > +
> > +     gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
> > +
> > +     return 0;
> >  }
> >  EXPORT_SYMBOL_GPL(gpiod_set_debounce);
> >
> > @@ -2723,6 +2733,7 @@ void gpiod_toggle_active_low(struct gpio_desc *desc)
> >  {
> >       VALIDATE_DESC_VOID(desc);
> >       change_bit(FLAG_ACTIVE_LOW, &desc->flags);
> > +     gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
> >  }
> >  EXPORT_SYMBOL_GPL(gpiod_toggle_active_low);
> >
> > @@ -3330,6 +3341,7 @@ int gpiod_set_consumer_name(struct gpio_desc *desc, const char *name)
> >
> >       kfree_const(desc->label);
> >       desc_set_label(desc, name);
> > +     gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
> >
> >       return 0;
> >  }
> > --
> > 2.39.2
> >

On Thu, Aug 24, 2023 at 11:27 AM Kent Gibson <warthog618@gmail.com> wrote:
>
> On Thu, Aug 24, 2023 at 11:11:18AM +0200, Bartosz Golaszewski wrote:
> > On Thu, Aug 24, 2023 at 11:08 AM Kent Gibson <warthog618@gmail.com> wrote:
> > >
> > > On Thu, Aug 24, 2023 at 10:55:44AM +0200, Bartosz Golaszewski wrote:
> > > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> > > >
> > > > We currently only emit CHANGED_CONFIG events when the user-space changes
> > > > GPIO config. We won't be notified if changes come from in-kernel. Let's
> > > > call the notifier chain whenever kernel users change direction or any of
> > > > the active-low, debounce or consumer name settings. We don't notify the
> > > > user-space about the persistence as the uAPI has no notion of it.
> > > >
> > > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> > > > ---
> > > > v1 -> v2:
> > > > - use the gpiod_line_state_notify() helper
> > > > - reorder the code in gpiod_set_debounce() for better readability
> > > >
> > > >  drivers/gpio/gpiolib.c | 16 ++++++++++++++--
> > > >  1 file changed, 14 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > > > index 40a0022ea719..1cb7731550ca 100644
> > > > --- a/drivers/gpio/gpiolib.c
> > > > +++ b/drivers/gpio/gpiolib.c
> > > > @@ -2439,6 +2439,7 @@ int gpiod_direction_input(struct gpio_desc *desc)
> > > >       }
> > > >       if (ret == 0) {
> > > >               clear_bit(FLAG_IS_OUT, &desc->flags);
> > > > +             gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
> > > >               ret = gpio_set_bias(desc);
> > > >       }
> > > >
> > >
> > > gpiod_direction_input() is called by cdev when a line is requested.
> > > So requesting a line now creates two events - REQUESTED and
> > > HANGED_CONFIG? Even worse - it calls gpiod_direction_input() first, so we
> > > will get CHANGED_CONFIG then REQUESTED??
> > >
> > > And a config change from cdev can call this and then generate a
> > > CHANGED_CONFIG event itself, so again double events.
> > >
> > > Same for output and probably debounce too (that one is a bit more
> > > convoluted).
> >
> > Ah, should have tested it with user-space too...
> >
> > Back to the drawing board I guess. May be the reason why we're not
> > doing it in the first place yet.
> >
>
> I think we were only looking at it from the userspace PoV, so what
> constitutes a "change" is only well defined when driven from userspace.
> This might be difficult to generalise without redefining what
> "changed" means, or providing cdev with a separate gpiolib API so you
> can tell whether the change is actually part of a cdev request, or ...
>
> So, yeah - more thought required.
>
> Got a use case that requires this, or just a nice to have?
>

I'm extending the virtual consumer driver and wanted to test from
user-spaces things like changing direction and other settings. I
figured it would make more sense to notify about all changes no matter
the source.

Bart