linux-kernel - Re: [PATCH 4/5] gpiolib: simplify notifying user-space about line requests

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Message-ID: <20241005094904.GA238189@rigel>
Date: Sat, 5 Oct 2024 17:49:04 +0800
From: Kent Gibson <warthog618@...il.com>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Linus Walleij <linus.walleij@...aro.org>, linux-gpio@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH 4/5] gpiolib: simplify notifying user-space about line
 requests

On Sat, Oct 05, 2024 at 11:34:26AM +0200, Bartosz Golaszewski wrote:
> On Sat, Oct 5, 2024 at 5:46 AM Kent Gibson <warthog618@...il.com> wrote:
> >
> > On Fri, Oct 04, 2024 at 04:43:25PM +0200, Bartosz Golaszewski wrote:
> > > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > >
> > > Instead of emitting the line state change event on request in three
> > > different places, just do it once, closer to the source: in
> > > gpiod_request_commit().
> > >
> > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > > ---
> > >  drivers/gpio/gpiolib-cdev.c | 6 ------
> > >  drivers/gpio/gpiolib.c      | 4 ++--
> > >  2 files changed, 2 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> > > index b0050250ac3a..f614a981253d 100644
> > > --- a/drivers/gpio/gpiolib-cdev.c
> > > +++ b/drivers/gpio/gpiolib-cdev.c
> > > @@ -372,8 +372,6 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
> > >                               goto out_free_lh;
> > >               }
> > >
> > > -             gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_REQUESTED);
> > > -
> > >               dev_dbg(&gdev->dev, "registered chardev handle for line %d\n",
> > >                       offset);
> >
> > This moves the notify to before the desc->flags have been set.
> > So the notified will now see the flags as previously set, not what they
> > have been requested as.
> >
>
> Ah, I got fooled by the libgpiod tests passing. I guess we should
> cover that first in tests-kernel-uapi.c.
>
> > That might be acceptible if you subsequently issue GPIO_V2_LINE_CHANGED_CONFIG
> > when the flags are set, but that is not done here and you explicitly don't
> > notify from here in patch 5 when you add notifying to gpiod_direction_output()
> > etc.
> >
>
> IMO it doesn't make sense to always emit REQUESTED and CONFIG_CHANGED
> events together. The initial config should be part of the request
> event. I'll get back to the drawing board.
>

Oh, I agree - that "might" is doing a lot of heavy lifting - there should
only be the one event.

Cheers,
Kent.