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>,
"Qiu, Tian Shu" <tian.shu.qiu@intel.com>
Subject: [PATCH v5 6/6] Documentation: ACPI: Document allow-low-power-probe _DSD property
Date: Mon, 10 Aug 2020 17:27:47 +0300 [thread overview]
Message-ID: <20200810142747.12400-7-sakari.ailus@linux.intel.com> (raw)
In-Reply-To: <20200810142747.12400-1-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/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
+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
+field and the "allow-low-power-probe" 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..0070fcde9e669 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/allow-low-power-probe
enumeration
osi
method-customizing
--
2.20.1
next prev parent reply other threads:[~2020-08-10 14:25 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-10 14:27 [PATCH v5 0/6] Support running driver's probe for a device powered off Sakari Ailus
2020-08-10 14:27 ` [PATCH v5 1/6] i2c: Allow driver to manage the device's power state during probe Sakari Ailus
2020-08-10 14:41 ` Sudeep Holla
2020-08-11 8:57 ` Sakari Ailus
2020-08-10 14:27 ` [PATCH v5 2/6] ACPI: Add a convenience function to tell a device is in low power state Sakari Ailus
2020-08-10 14:27 ` [PATCH v5 3/6] ov5670: Support probe whilst the device is in a " Sakari Ailus
2020-08-12 9:12 ` Bingbu Cao
2020-08-12 9:22 ` Sakari Ailus
2020-08-14 4:49 ` Bingbu Cao
2020-08-10 14:27 ` [PATCH v5 4/6] media: i2c: imx319: Support probe while the device is off Sakari Ailus
2020-08-10 14:27 ` [PATCH v5 5/6] at24: Support probing while off Sakari Ailus
2020-08-10 14:27 ` Sakari Ailus [this message]
2020-08-14 4:11 ` [PATCH v5 0/6] Support running driver's probe for a device powered off Bingbu Cao
2020-08-14 6:18 ` Bingbu Cao
2020-08-14 13:17 ` Tomasz Figa
2020-08-18 11:04 ` Sakari Ailus
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