linux-kernel - Re: New sysfs interface for privacy screens

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Date:   Tue, 1 Oct 2019 10:42:58 -0600
From:   Mat King <mathewk@...gle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        rafael@...nel.org, Ross Zwisler <zwisler@...gle.com>,
        Rajat Jain <rajatja@...gle.com>,
        Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>
Subject: Re: New sysfs interface for privacy screens

On Tue, Oct 1, 2019 at 10:27 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Tue, Oct 01, 2019 at 10:09:46AM -0600, Mat King wrote:
> > Resending in plain text mode
> >
> > I have been looking into adding Linux support for electronic privacy
> > screens which is a feature on some new laptops which is built into the
> > display and allows users to turn it on instead of needing to use a
> > physical privacy filter. In discussions with my colleagues the idea of
> > using either /sys/class/backlight or /sys/class/leds but this new
> > feature does not seem to quite fit into either of those classes.
> >
> > I am proposing adding a class called "privacy_screen" to interface
> > with these devices. The initial API would be simple just a single
> > property called "privacy_state" which when set to 1 would mean that
> > privacy is enabled and 0 when privacy is disabled.
> >
> > Current known use cases will use ACPI _DSM in order to interface with
> > the privacy screens, but this class would allow device driver authors
> > to use other interfaces as well.
> >
> > Example:
> >
> > # get privacy screen state
> > cat /sys/class/privacy_screen/cros_privacy/privacy_state # 1: privacy
> > enabled 0: privacy disabled
> >
> > # set privacy enabled
> > echo 1 > /sys/class/privacy_screen/cros_privacy/privacy_state
>
> What is "cros_privacy" here?

This would be set by the device driver. This example would be for a
Chrome OS privacy screen device, but the driver would set the name
just like in the backlight class.

>
> >  Does this approach seem to be reasonable?
>
> Seems sane to me, do you have any code that implements this so we can
> see it?

It is still early in the implementation so there is no code quite yet.
I wanted to get some general feedback on the approach first. As soon
as I have code to share I will post it.

>
> thanks,
>
> greg k-h

Thank you for the feedback.