linux-kernel - Re: [PATCH v4 00/13] gpiolib: add an ioctl() for monitoring line status changes

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Date:   Tue, 7 Jan 2020 11:38:37 +0100
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        Kent Gibson <warthog618@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 00/13] gpiolib: add an ioctl() for monitoring line
 status changes

wt., 7 sty 2020 o 11:07 Linus Walleij <linus.walleij@...aro.org> napisał(a):
>
> On Tue, Dec 24, 2019 at 1:07 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> > From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> >
> > When discussing the recent user-space changes with Kent and while working
> > on dbus API for libgpiod I noticed that we really don't have any way of
> > keeping the line info synchronized between the kernel and user-space
> > processes. We can of course periodically re-read the line information or
> > even do it every time we want to read a property but this isn't optimal.
> >
> > This series adds a new ioctl() that allows user-space to set up a watch on
> > the GPIO chardev file-descriptor which can then be polled for events
> > emitted by the kernel when the line is requested, released or its status
> > changed. This of course doesn't require the line to be requested. Multiple
> > user-space processes can watch the same lines.
> >
> > This series also includes a variety of minor tweaks & fixes for problems
> > discovered during development. For instance it addresses a race-condition
> > in current line event fifo.
>
> The patch set overall looks good to me, I don't understand the kfifo
> parts but I trust you on this, though we need review from a FIFO
> maintainer.

Ha! This may be a problem - there doesn't seem to be one. This is why
I Cc'd Greg.

>
> Could you send me a pull request of the first patches before the
> FIFO changes start, they are good cleanups on their own, also
> it brings down the size of your patch stack.

Sure, will do.

>
> Yours,
> Linus Walleij

Bart