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@xxxxxxxxxxxxxxx> > > --- > > .../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
