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From:   Jani Nikula <jani.nikula@linux.intel.com>
To:     Mat King <mathewk@google.com>, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org
Cc:     Daniel Thompson <daniel.thompson@linaro.org>, rafael@kernel.org,
        gregkh@linuxfoundation.org, Ross Zwisler <zwisler@google.com>,
        Jingoo Han <jingoohan1@gmail.com>,
        Rajat Jain <rajatja@google.com>,
        Lee Jones <lee.jones@linaro.org>,
        Ville =?utf-8?B?U3lyasOkbMOk?= <ville.syrjala@linux.intel.com>
Subject: Re: New sysfs interface for privacy screens
In-Reply-To: <CAL_quvRknSSVvXN3q_Se0hrziw2oTNS3ENNoeHYhvciCRq9Yww@mail.gmail.com>
Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo
References: <CAL_quvRknSSVvXN3q_Se0hrziw2oTNS3ENNoeHYhvciCRq9Yww@mail.gmail.com>
Date:   Wed, 02 Oct 2019 12:30:05 +0300
Message-ID: <87h84rbile.fsf@intel.com>
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On Tue, 01 Oct 2019, Mat King <mathewk@google.com> 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
>
>  Does this approach seem to be reasonable?

What part of the userspace would be managing the privacy screen? Should
there be a connection between the display and the privacy screen that
covers the display? How would the userspace make that connection if it's
a sysfs interface?

I don't know how the privacy screen operates, but if it draws any power,
you'll want to disable it when you switch off the display it covers.

If the privacy screen control was part of the graphics subsystem (say, a
DRM connector property, which feels somewhat natural), I think it would
make it easier for userspace to have policies such as enabling the
privacy screen automatically depending on the content you're viewing,
but only if the content is on the display that has a privacy screen.


BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center