linux-kernel - Re: [PATCH v2 10/11] gpiolib: add new ioctl() for monitoring changes in line info

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Message-ID: <CAHp75VdiAtHtdrUP2EmLULh86oO37ha8si10gFKYRavXCEwRRQ@mail.gmail.com>
Date:   Thu, 5 Dec 2019 00:34:07 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Kent Gibson <warthog618@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v2 10/11] gpiolib: add new ioctl() for monitoring changes
 in line info

On Wed, Dec 4, 2019 at 6:03 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
>
> Currently there is no way for user-space to be informed about changes
> in status of GPIO lines e.g. when someone else requests the line or its
> config changes. We can only periodically re-read the line-info. This
> is fine for simple one-off user-space tools, but any daemon that provides
> a centralized access to GPIO chips would benefit hugely from an event
> driven line info synchronization.
>
> This patch adds a new ioctl() that allows user-space processes to reuse
> the file descriptor associated with the character device for watching
> any changes in line properties. Every such event contains the updated
> line information.
>
> Currently the events are generated on three types of status changes: when
> a line is requested, when it's released and when its config is changed.
> The first two are self-explanatory. For the third one: this will only
> happen when another user-space process calls the new SET_CONFIG ioctl()
> as any changes that can happen from within the kernel (i.e.
> set_transitory() or set_debounce()) are of no interest to user-space.

> +/**
> + * struct gpioline_info_changed - Information about a change in status
> + * of a GPIO line
> + * @timestamp: estimate of time of status change occurrence, in nanoseconds
> + * @event_type: one of GPIOLINE_CHANGED_REQUESTED, GPIOLINE_CHANGED_RELEASED
> + * and GPIOLINE_CHANGED_CONFIG
> + * @info: updated line information
> + */
> +struct gpioline_info_changed {
> +       __u64 timestamp;
> +       __u32 event_type;
> +       struct gpioline_info info;
> +       __u32 padding[4]; /* for future use */
> +};

Has this been tested against 64-bit kernel / 32-bit userspace case?

-- 
With Best Regards,
Andy Shevchenko