linux-kernel - Re: [PATCH v2 1/1] drivers/misc: add a driver for HPS

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Date:   Fri, 4 Feb 2022 16:27:05 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Sami Kyöstilä <skyostil@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, dtor@...omium.org,
        arnd@...db.de, evanbenn@...omium.org
Subject: Re: [PATCH v2 1/1] drivers/misc: add a driver for HPS

On Wed, Feb 02, 2022 at 03:49:37PM +1100, Sami Kyöstilä wrote:
> This patch introduces a driver for the ChromeOS screen privacy
> sensor (aka. HPS). The driver supports a sensor connected to the I2C bus
> and identified as "GOOG0020" in the ACPI tables.
> 
> When loaded, the driver exports the sensor to userspace through a
> character device. This device only supports power management, i.e.,
> communication with the sensor must be done through regular I2C
> transmissions from userspace.
> 
> Power management is implemented by enabling the respective power GPIO
> while at least one userspace process holds an open fd on the character
> device. By default, the device is powered down if there are no active
> clients.
> 
> Note that the driver makes no effort to preserve the state of the sensor
> between power down and power up events. Userspace is responsible for
> reinitializing any needed state once power has been restored.
> 
> The device firmware, I2C protocol and other documentation is available
> at https://chromium.googlesource.com/chromiumos/platform/hps-firmware.
> 
> Signed-off-by: Sami Kyöstilä <skyostil@...omium.org>
> ---
> 
> Changes in v2:
> - Removed custom ioctl interface.
> - Reworked to use miscdev.
> 
>  MAINTAINERS            |   6 ++
>  drivers/misc/Kconfig   |  10 +++
>  drivers/misc/Makefile  |   1 +
>  drivers/misc/hps-i2c.c | 184 +++++++++++++++++++++++++++++++++++++++++

Why isn't this in drivers/platform/chrome/ instead?

And what can you do with this hardware when it is enabled?  What
userspace tool uses it?

thanks,

greg k-h