From: Sakari Ailus <sakari.ailus@linux.intel.com>
To: linux-i2c@vger.kernel.org
Cc: Wolfram Sang <wsa@the-dreams.de>,
"Rafael J. Wysocki" <rafael@kernel.org>,
linux-acpi@vger.kernel.org, Bingbu Cao <bingbu.cao@intel.com>,
linux-media@vger.kernel.org,
Chiranjeevi Rapolu <chiranjeevi.rapolu@intel.com>,
Hyungwoo Yang <hyungwoo.yang@intel.com>,
Bartosz Golaszewski <bgolaszewski@baylibre.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-kernel@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
rajmohan.mani@intel.com, Tomasz Figa <tfiga@chromium.org>
Subject: [PATCH v4 6/6] Documentation: ACPI: Document probe-low-power _DSD property
Date: Tue, 21 Jan 2020 15:41:57 +0200 [thread overview]
Message-ID: <20200121134157.20396-7-sakari.ailus@linux.intel.com> (raw)
In-Reply-To: <20200121134157.20396-1-sakari.ailus@linux.intel.com>
Document the probe-low-power _DSD property and how it is used with I²C
drivers.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
.../acpi/dsd/probe-low-power.rst | 28 +++++++++++++++++++
Documentation/firmware-guide/acpi/index.rst | 1 +
2 files changed, 29 insertions(+)
create mode 100644 Documentation/firmware-guide/acpi/dsd/probe-low-power.rst
diff --git a/Documentation/firmware-guide/acpi/dsd/probe-low-power.rst b/Documentation/firmware-guide/acpi/dsd/probe-low-power.rst
new file mode 100644
index 0000000000000..e0343ffefe071
--- /dev/null
+++ b/Documentation/firmware-guide/acpi/dsd/probe-low-power.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. The _DSD property
+"probe-low-power" has been defined for this purpose.
+
+How it works
+============
+
+The property "probe-low-power" boolean property may be used to tell Linux
+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 in its struct i2c_driver.probe_low_power field and the
+"probe-low-power" property is present, the device will not be powered on
+for probe.
+
+The downside is that as the device is not powered on, even if there's a
+problem with the device, the driver likely probes just fine but the first
+user will find out the device doesn't work, instead of a failure at probe
+time. This feature should thus be used sparingly.
diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst
index ad3b5afdae77e..4e4ac675c0ff8 100644
--- a/Documentation/firmware-guide/acpi/index.rst
+++ b/Documentation/firmware-guide/acpi/index.rst
@@ -11,6 +11,7 @@ ACPI Support
dsd/graph
dsd/data-node-references
dsd/leds
+ dsd/probe-low-power
enumeration
osi
method-customizing
--
2.20.1
next prev parent reply other threads:[~2020-01-21 13:41 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-21 13:41 [PATCH v4 0/6] Support running driver's probe for a device powered off Sakari Ailus
2020-01-21 13:41 ` [PATCH v4 1/6] i2c: Allow driver to manage the device's power state during probe Sakari Ailus
2020-01-29 13:54 ` Bartosz Golaszewski
2020-03-23 21:36 ` Sakari Ailus
2020-01-21 13:41 ` [PATCH v4 2/6] ACPI: Add a convenience function to tell a device is in low power state Sakari Ailus
2020-01-21 16:07 ` Rafael J. Wysocki
2020-01-21 13:41 ` [PATCH v4 3/6] ov5670: Support probe whilst the device is in a " Sakari Ailus
2020-01-21 13:41 ` [PATCH v4 4/6] media: i2c: imx319: Support probe while the device is off Sakari Ailus
2020-01-21 13:41 ` [PATCH v4 5/6] at24: Support probing while off Sakari Ailus
2020-01-29 13:36 ` Bartosz Golaszewski
2020-03-11 8:55 ` Sakari Ailus
2020-03-12 13:10 ` Bartosz Golaszewski
2020-03-23 21:31 ` Sakari Ailus
2020-03-25 13:48 ` Bartosz Golaszewski
2020-08-10 8:25 ` Sakari Ailus
2020-08-10 18:12 ` Bartosz Golaszewski
2020-08-11 8:00 ` Sakari Ailus
2020-08-12 18:07 ` Bartosz Golaszewski
2020-08-12 19:25 ` Wolfram Sang
2020-08-12 19:33 ` Bartosz Golaszewski
2020-01-21 13:41 ` Sakari Ailus [this message]
2020-01-21 16:09 ` [PATCH v4 6/6] Documentation: ACPI: Document probe-low-power _DSD property Rafael J. Wysocki
2020-01-21 16:18 ` Sakari Ailus
2020-01-21 16:56 ` Rafael J. Wysocki
2020-01-21 16:58 ` Sakari Ailus
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