linux-kernel - Re: [PATCH v6 6/6] Documentation: ACPI: Document allow-low-power-probe

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Message-ID: <20200827132822.GI24582@paasikivi.fi.intel.com>
Date:   Thu, 27 Aug 2020 16:28:22 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     linux-i2c@...r.kernel.org, Wolfram Sang <wsa@...-dreams.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-acpi@...r.kernel.org, Bingbu Cao <bingbu.cao@...el.com>,
        linux-media@...r.kernel.org,
        Chiranjeevi Rapolu <chiranjeevi.rapolu@...el.com>,
        Hyungwoo Yang <hyungwoo.yang@...el.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rajmohan.mani@...el.com, Tomasz Figa <tfiga@...omium.org>,
        "Qiu, Tian Shu" <tian.shu.qiu@...el.com>
Subject: Re: [PATCH v6 6/6] Documentation: ACPI: Document
 allow-low-power-probe _DSD property

On Wed, Aug 26, 2020 at 11:06:22AM -0700, Randy Dunlap wrote:
> On 8/26/20 4:54 AM, Sakari Ailus wrote:
> > Document the probe-low-power _DSD property and how it is used with I²C
> > drivers.
> > 
> > Signed-off-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> > ---
> >  .../acpi/dsd/allow-low-power-probe.rst        | 28 +++++++++++++++++++
> >  Documentation/firmware-guide/acpi/index.rst   |  1 +
> >  2 files changed, 29 insertions(+)
> >  create mode 100644 Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> > 
> > diff --git a/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> > new file mode 100644
> > index 0000000000000..6fcc89162b898
> > --- /dev/null
> > +++ b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> > @@ -0,0 +1,28 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +======================================
> > +Probing I²C devices in low power state
> > +======================================
> > +
> > +Introduction
> > +============
> > +
> > +In some cases it may be preferred to leave certain devices powered off for the
> > +entire system bootup if powering on these devices has adverse side effects,
> > +beyond just powering on the said device. Linux recognizes the _DSD property
> > +"allow-low-power-probe" that can be used for this purpose.
> > +
> > +How it works
> > +============
> > +
> > +The property "allow-low-power-probe" boolean property may be used to tell Linux
> 
> Drop the first "property".
> 

Thanks, will fix for v7.

> > +that the I²C framework should instruct the kernel ACPI framework to leave the
> > +device in the low power state. If the driver indicates its support for this by
> > +setting the I2C_DRV_FL_ALLOW_LOW_POWER_PROBE flag in struct i2c_driver.flags

This is leftover from v5 actually, I'll change the documentation to mention
the allow_low_power_probe as well.

> > +field and the "allow-low-power-probe" property is present, the device will not
> > +be powered on for probe.
> 

-- 
Kind regards,

Sakari Ailus