Re: [RFC] gpio: expose pull-up/pull-down line flags to userspace

[Kent Gibson <warthog618@xxxxxxxxx>]

On Tue, Oct 08, 2019 at 10:56:18PM +0200, Bartosz Golaszewski wrote:
> wt., 8 paź 2019 o 08:15 Kent Gibson <warthog618@xxxxxxxxx> napisał(a):
> >
> > On Sat, Sep 21, 2019 at 12:25:23PM +0200, Drew Fustini wrote:
> > > Add pull-up/pull-down flags to the gpio line get and
> > > set ioctl() calls.  Use cases include a push button
> > > that does not have an external resistor.
> > >
> > > Addition use cases described by Limor Fried (ladyada) of
> > > Adafruit in this PR for Adafruit_Blinka Python lib:
> > > https://github.com/adafruit/Adafruit_Blinka/pull/59
> > >
> > > Signed-off-by: Drew Fustini <drew@xxxxxxxx>
> > > ---
> > >  drivers/gpio/gpiolib.c    | 12 ++++++++++++
> > >  include/uapi/linux/gpio.h |  4 ++++
> > >  2 files changed, 16 insertions(+)
> > >
> > > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > > index d9074191edef..9da1093cc7f5 100644
> > > --- a/drivers/gpio/gpiolib.c
> > > +++ b/drivers/gpio/gpiolib.c
> > > @@ -427,6 +427,8 @@ struct linehandle_state {
> > >       (GPIOHANDLE_REQUEST_INPUT | \
> > >       GPIOHANDLE_REQUEST_OUTPUT | \
> > >       GPIOHANDLE_REQUEST_ACTIVE_LOW | \
> > > +     GPIOHANDLE_REQUEST_PULL_UP | \
> > > +     GPIOHANDLE_REQUEST_PULL_DOWN | \
> > >       GPIOHANDLE_REQUEST_OPEN_DRAIN | \
> > >       GPIOHANDLE_REQUEST_OPEN_SOURCE)
> > >
> > > @@ -598,6 +600,10 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
> > >                       set_bit(FLAG_OPEN_DRAIN, &desc->flags);
> > >               if (lflags & GPIOHANDLE_REQUEST_OPEN_SOURCE)
> > >                       set_bit(FLAG_OPEN_SOURCE, &desc->flags);
> > > +             if (lflags & GPIOHANDLE_REQUEST_PULL_DOWN)
> > > +                     set_bit(FLAG_PULL_DOWN, &desc->flags);
> > > +             if (lflags & GPIOHANDLE_REQUEST_PULL_UP)
> > > +                     set_bit(FLAG_PULL_UP, &desc->flags);
> > >
> > >               ret = gpiod_set_transitory(desc, false);
> > >               if (ret < 0)
> > > @@ -1102,6 +1108,10 @@ static long gpio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> > >               if (test_bit(FLAG_OPEN_SOURCE, &desc->flags))
> > >                       lineinfo.flags |= (GPIOLINE_FLAG_OPEN_SOURCE |
> > >                                          GPIOLINE_FLAG_IS_OUT);
> > > +             if (test_bit(FLAG_PULL_DOWN, &desc->flags))
> > > +                     lineinfo.flags |= GPIOLINE_FLAG_PULL_DOWN;
> > > +             if (test_bit(FLAG_PULL_UP, &desc->flags))
> > > +                     lineinfo.flags |= GPIOLINE_FLAG_PULL_UP;
> > >
> > >               if (copy_to_user(ip, &lineinfo, sizeof(lineinfo)))
> > >                       return -EFAULT;
> > > @@ -2475,6 +2485,8 @@ static bool gpiod_free_commit(struct gpio_desc *desc)
> > >               clear_bit(FLAG_REQUESTED, &desc->flags);
> > >               clear_bit(FLAG_OPEN_DRAIN, &desc->flags);
> > >               clear_bit(FLAG_OPEN_SOURCE, &desc->flags);
> > > +             clear_bit(FLAG_PULL_UP, &desc->flags);
> > > +             clear_bit(FLAG_PULL_DOWN, &desc->flags);
> > >               clear_bit(FLAG_IS_HOGGED, &desc->flags);
> > >               ret = true;
> > >       }
> > > diff --git a/include/uapi/linux/gpio.h b/include/uapi/linux/gpio.h
> > > index 4ebfe0ac6c5b..c2d1f7d908d6 100644
> > > --- a/include/uapi/linux/gpio.h
> > > +++ b/include/uapi/linux/gpio.h
> > > @@ -33,6 +33,8 @@ struct gpiochip_info {
> > >  #define GPIOLINE_FLAG_ACTIVE_LOW     (1UL << 2)
> > >  #define GPIOLINE_FLAG_OPEN_DRAIN     (1UL << 3)
> > >  #define GPIOLINE_FLAG_OPEN_SOURCE    (1UL << 4)
> > > +#define GPIOLINE_FLAG_PULL_UP        (1UL << 5)
> > > +#define GPIOLINE_FLAG_PULL_DOWN      (1UL << 6)
> > >
> > >  /**
> > >   * struct gpioline_info - Information about a certain GPIO line
> > > @@ -62,6 +64,8 @@ struct gpioline_info {
> > >  #define GPIOHANDLE_REQUEST_ACTIVE_LOW        (1UL << 2)
> > >  #define GPIOHANDLE_REQUEST_OPEN_DRAIN        (1UL << 3)
> > >  #define GPIOHANDLE_REQUEST_OPEN_SOURCE       (1UL << 4)
> > > +#define GPIOHANDLE_REQUEST_PULL_UP   (1UL << 5)
> > > +#define GPIOHANDLE_REQUEST_PULL_DOWN (1UL << 6)
> > >
> > >  /**
> > >   * struct gpiohandle_request - Information about a GPIO handle request
> > > --
> > > 2.20.1
> > >
> > Sorry for the late feedback, but I'm still not sure whether this patch
> > is on track to be applied or not.  I had thought not, at least not yet,
> > but just in case...
> >
> 
> It still needs some fixes, but Linus seems to be fine with the general idea.
> 
> > You have added the flags to linehandle_create, but not lineevent_create.
> > Given that your primary use case is push buttons, isn't the event request
> > at least as important as the handle request?  Even ignoring your use
> > case, I'd add them to lineevent_create just to maintain symmetry.
> >
> > Also, is it valid to set PULL_UP and PULL_DOWN simulaneously?
> > I would think not, but I could be wrong.
> > If not then that combination should be rejected with EINVAL.
> >
> 
> Yes, some validity checks of the flags must be added. I even did it in
> my local branch[1].
>
Your changes for linehandle_create look ok, but for lineevent_create
you explicitly disabled PULL_UP and PULL_DOWN, and in a block labelled
"This is just wrong: we don't look for events on output lines" at that.

> Re: direction and configuration changes on requested lines: I think
> it's quite useful to add in the form of a new ioctl():
> GPIOHANDLE_SET_CONFIG_IOCTL or something. I started hacking on this
> but eventually got more busy this week than I anticipated. I'm still
> planning on sending an RFC by the end of the week though.
>
I have the reverse problem - bored and looking for something to do, so
more than willing to help out - if you want it.

And while we're talking, does the gpio-mockup support pull up/down
being set from the kernel side?

Cheers,
Kent.
> 
> [1] https://github.com/brgl/linux/commit/82fc38f6ab599ee03f7a8ed078de8abb41e6e611
> 
> > Cheers,
> > Kent.