Document the use of the _DSC object for setting desirable power state
during probe.
Signed-off-by: Sakari Ailus <[email protected]>
Reviewed-by: Tomasz Figa <[email protected]>
---
Documentation/firmware-guide/acpi/index.rst | 1 +
.../firmware-guide/acpi/non-d0-probe.rst | 78 +++++++++++++++++++
2 files changed, 79 insertions(+)
create mode 100644 Documentation/firmware-guide/acpi/non-d0-probe.rst
diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst
index a99ee402b212b..b053b0c3d6969 100644
--- a/Documentation/firmware-guide/acpi/index.rst
+++ b/Documentation/firmware-guide/acpi/index.rst
@@ -26,5 +26,6 @@ ACPI Support
acpi-lid
lpit
video_extension
+ non-d0-probe
extcon-intel-int3496
intel-pmc-mux
diff --git a/Documentation/firmware-guide/acpi/non-d0-probe.rst b/Documentation/firmware-guide/acpi/non-d0-probe.rst
new file mode 100644
index 0000000000000..78781e1ab6a3d
--- /dev/null
+++ b/Documentation/firmware-guide/acpi/non-d0-probe.rst
@@ -0,0 +1,78 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+========================================
+Probing devices in other D states than 0
+========================================
+
+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.
+
+How it works
+============
+
+The _DSC (Device State for Configuration) object that evaluates to an integer
+may be used to tell Linux the highest allowed D state for a device during
+probe. The support for _DSC requires support from the kernel bus type if the
+bus driver normally sets the device in D0 state for probe.
+
+The downside of using _DSC 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.
+
+I²C
+---
+
+If an I²C driver indicates its support for this by setting the
+I2C_DRV_ACPI_WAIVE_D0_PROBE flag in struct i2c_driver.flags field and the
+_DSC object evaluates to integer higher than the D state of the device,
+the device will not be powered on (put in D0 state) for probe.
+
+D states
+--------
+
+The D states and thus also the allowed values for _DSC are listed below. Refer
+to [1] for more information on device power states.
+
+.. code-block:: text
+
+ Number State Description
+ 0 D0 Device fully powered on
+ 1 D1
+ 2 D2
+ 3 D3hot
+ 4 D3cold Off
+
+References
+==========
+
+[1] https://uefi.org/specifications/ACPI/6.4/02_Definition_of_Terms/Definition_of_Terms.html#device-power-state-definitions
+
+Example
+=======
+
+An ASL example describing an ACPI device using _DSC object to tell Operating
+System the device should remain powered off during probe looks like this. Some
+objects not relevant from the example point of view have been omitted.
+
+.. code-block:: text
+
+ Device (CAM0)
+ {
+ Name (_HID, "SONY319A")
+ Name (_UID, Zero)
+ Name (_CRS, ResourceTemplate ()
+ {
+ I2cSerialBus(0x0020, ControllerInitiated, 0x00061A80,
+ AddressingMode7Bit, "\\_SB.PCI0.I2C0",
+ 0x00, ResourceConsumer)
+ })
+ Name (_DSC, 0, NotSerialized)
+ {
+ Return (0x4)
+ }
+ }
--
2.30.2
Sakari,
On 10/18/21 8:17 PM, Sakari Ailus wrote:
> Document the use of the _DSC object for setting desirable power state
> during probe.
>
> Signed-off-by: Sakari Ailus <[email protected]>
> Reviewed-by: Tomasz Figa <[email protected]>
> ---
> Documentation/firmware-guide/acpi/index.rst | 1 +
> .../firmware-guide/acpi/non-d0-probe.rst | 78 +++++++++++++++++++
> 2 files changed, 79 insertions(+)
> create mode 100644 Documentation/firmware-guide/acpi/non-d0-probe.rst
>
> diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst
> index a99ee402b212b..b053b0c3d6969 100644
> --- a/Documentation/firmware-guide/acpi/index.rst
> +++ b/Documentation/firmware-guide/acpi/index.rst
> @@ -26,5 +26,6 @@ ACPI Support
> acpi-lid
> lpit
> video_extension
> + non-d0-probe
> extcon-intel-int3496
> intel-pmc-mux
> diff --git a/Documentation/firmware-guide/acpi/non-d0-probe.rst b/Documentation/firmware-guide/acpi/non-d0-probe.rst
> new file mode 100644
> index 0000000000000..78781e1ab6a3d
> --- /dev/null
> +++ b/Documentation/firmware-guide/acpi/non-d0-probe.rst
> @@ -0,0 +1,78 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +========================================
> +Probing devices in other D states than 0
> +========================================
> +
> +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.
> +
> +How it works
> +============
> +
> +The _DSC (Device State for Configuration) object that evaluates to an integer
> +may be used to tell Linux the highest allowed D state for a device during
> +probe. The support for _DSC requires support from the kernel bus type if the
> +bus driver normally sets the device in D0 state for probe.
> +
> +The downside of using _DSC 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.
> +
> +I?C
> +---
> +
> +If an I?C driver indicates its support for this by setting the
> +I2C_DRV_ACPI_WAIVE_D0_PROBE flag in struct i2c_driver.flags field and the
> +_DSC object evaluates to integer higher than the D state of the device,
> +the device will not be powered on (put in D0 state) for probe.
> +
> +D states
> +--------
> +
> +The D states and thus also the allowed values for _DSC are listed below. Refer
> +to [1] for more information on device power states.
> +
> +.. code-block:: text
> +
> + Number State Description
> + 0 D0 Device fully powered on
> + 1 D1
> + 2 D2
> + 3 D3hot
> + 4 D3cold Off
> +
> +References
> +==========
> +
> +[1] https://uefi.org/specifications/ACPI/6.4/02_Definition_of_Terms/Definition_of_Terms.html#device-power-state-definitions
> +
> +Example
> +=======
> +
> +An ASL example describing an ACPI device using _DSC object to tell Operating
> +System the device should remain powered off during probe looks like this. Some
> +objects not relevant from the example point of view have been omitted.
> +
> +.. code-block:: text
> +
> + Device (CAM0)
> + {
> + Name (_HID, "SONY319A")
> + Name (_UID, Zero)
> + Name (_CRS, ResourceTemplate ()
> + {
> + I2cSerialBus(0x0020, ControllerInitiated, 0x00061A80,
> + AddressingMode7Bit, "\\_SB.PCI0.I2C0",
> + 0x00, ResourceConsumer)
> + })
> + Name (_DSC, 0, NotSerialized)
> + {
> + Return (0x4)
> + }
One question here:
Is the value of _DSC object evaluated from 'Method' or 'Name' ?
> + }
>
--
Best regards,
Bingbu Cao
Hi Bingbu,
On Mon, Oct 25, 2021 at 07:01:41PM +0800, Bingbu Cao wrote:
> Sakari,
>
> On 10/18/21 8:17 PM, Sakari Ailus wrote:
> > Document the use of the _DSC object for setting desirable power state
> > during probe.
> >
> > Signed-off-by: Sakari Ailus <[email protected]>
> > Reviewed-by: Tomasz Figa <[email protected]>
> > ---
> > Documentation/firmware-guide/acpi/index.rst | 1 +
> > .../firmware-guide/acpi/non-d0-probe.rst | 78 +++++++++++++++++++
> > 2 files changed, 79 insertions(+)
> > create mode 100644 Documentation/firmware-guide/acpi/non-d0-probe.rst
> >
> > diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst
> > index a99ee402b212b..b053b0c3d6969 100644
> > --- a/Documentation/firmware-guide/acpi/index.rst
> > +++ b/Documentation/firmware-guide/acpi/index.rst
> > @@ -26,5 +26,6 @@ ACPI Support
> > acpi-lid
> > lpit
> > video_extension
> > + non-d0-probe
> > extcon-intel-int3496
> > intel-pmc-mux
> > diff --git a/Documentation/firmware-guide/acpi/non-d0-probe.rst b/Documentation/firmware-guide/acpi/non-d0-probe.rst
> > new file mode 100644
> > index 0000000000000..78781e1ab6a3d
> > --- /dev/null
> > +++ b/Documentation/firmware-guide/acpi/non-d0-probe.rst
> > @@ -0,0 +1,78 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +========================================
> > +Probing devices in other D states than 0
> > +========================================
> > +
> > +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.
> > +
> > +How it works
> > +============
> > +
> > +The _DSC (Device State for Configuration) object that evaluates to an integer
> > +may be used to tell Linux the highest allowed D state for a device during
> > +probe. The support for _DSC requires support from the kernel bus type if the
> > +bus driver normally sets the device in D0 state for probe.
> > +
> > +The downside of using _DSC 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.
> > +
> > +I?C
> > +---
> > +
> > +If an I?C driver indicates its support for this by setting the
> > +I2C_DRV_ACPI_WAIVE_D0_PROBE flag in struct i2c_driver.flags field and the
> > +_DSC object evaluates to integer higher than the D state of the device,
> > +the device will not be powered on (put in D0 state) for probe.
> > +
> > +D states
> > +--------
> > +
> > +The D states and thus also the allowed values for _DSC are listed below. Refer
> > +to [1] for more information on device power states.
> > +
> > +.. code-block:: text
> > +
> > + Number State Description
> > + 0 D0 Device fully powered on
> > + 1 D1
> > + 2 D2
> > + 3 D3hot
> > + 4 D3cold Off
> > +
> > +References
> > +==========
> > +
> > +[1] https://uefi.org/specifications/ACPI/6.4/02_Definition_of_Terms/Definition_of_Terms.html#device-power-state-definitions
> > +
> > +Example
> > +=======
> > +
> > +An ASL example describing an ACPI device using _DSC object to tell Operating
> > +System the device should remain powered off during probe looks like this. Some
> > +objects not relevant from the example point of view have been omitted.
> > +
> > +.. code-block:: text
> > +
> > + Device (CAM0)
> > + {
> > + Name (_HID, "SONY319A")
> > + Name (_UID, Zero)
> > + Name (_CRS, ResourceTemplate ()
> > + {
> > + I2cSerialBus(0x0020, ControllerInitiated, 0x00061A80,
> > + AddressingMode7Bit, "\\_SB.PCI0.I2C0",
> > + 0x00, ResourceConsumer)
> > + })
> > + Name (_DSC, 0, NotSerialized)
> > + {
> > + Return (0x4)
> > + }
> One question here:
> Is the value of _DSC object evaluated from 'Method' or 'Name' ?
"Method". This is a bug in the documentation. Thanks!
Rafael: could you fix this while applying?
--
Sakari Ailus