linux-kernel - Re: [PATCH v2 6/6] gpiolib: notify user-space about in-kernel line state changes

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Message-ID: <20241014022433.GD20620@rigel>
Date: Mon, 14 Oct 2024 10:24:33 +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 v2 6/6] gpiolib: notify user-space about in-kernel line
 state changes

On Thu, Oct 10, 2024 at 11:10:27AM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>
> We currently only notify user-space about line config changes that are
> made from user-space. Any kernel config changes are not signalled.
>
> Let's improve the situation by emitting the events closer to the source.
> To that end let's call the relevant notifier chain from the functions
> setting direction, gpiod_set_config(), gpiod_set_consumer_name() and
> gpiod_toggle_active_low(). This covers all the options that we can
> inform the user-space about. We ignore events which don't have
> corresponding flags exported to user-space on purpose - otherwise the
> user would see a config-changed event but the associated line-info would
> remain unchanged.
>
> gpiod_direction_output/input() can be called from any context.
> Fortunately, we now emit line state events using an atomic notifier
> chain, so it's no longer an issue.
>
> Let's also add non-notifying wrappers around the direction setters in
> order to not emit superfluous reconfigure events when requesting the
> lines as the initial config should be part of the request notification.
>

So lines requested from kernel space will result in a LINE_REQUESTED and
then a series of LINE_CHANGED_CONFIG?  Whereas for lines requested from
userspace those will be collapsed into the one LINE_REQUESTED event?
That's not ideal, but I realise making the rest of the kernel behave as
per cdev would be non-trivial, so ok - it all comes out in the wash.
And it is clearly better than nothing.

Cheers,
Kent.