Document the probe-low-power _DSD property and how it is used with I²C
drivers.
Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
---
.../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
