linux-kernel - Re: [RESEND PATCH v5 6/7] gpiolib: add new ioctl() for monitoring changes in line info

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Date:   Thu, 23 Jan 2020 16:49:35 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Kent Gibson <warthog618@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Stefani Seibold <stefani@...bold.net>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [RESEND PATCH v5 6/7] gpiolib: add new ioctl() for monitoring
 changes in line info

On Thu, Jan 23, 2020 at 03:05:05PM +0100, Bartosz Golaszewski 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.

...

> +	ret = kfifo_in_spinlocked(&priv->events, &chg,
> +				  1, &priv->wait.lock);

At least 1 can be moved to previous line.
(No need for new version, I hope you can fix this when applying)

> +	if (ret)
> +		wake_up_poll(&priv->wait, EPOLLIN);
> +	else
> +		pr_debug_ratelimited("lineinfo event FIFO is full - event dropped\n");
> +
> +	return NOTIFY_OK;
> +}

-- 
With Best Regards,
Andy Shevchenko