[v4,6/6] Documentation: ACPI: Document probe-low-power _DSD property
diff mbox series

Message ID 20200121134157.20396-7-sakari.ailus@linux.intel.com
State Changes Requested
Headers show
Series
  • Support running driver's probe for a device powered off
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Commit Message

Sakari Ailus Jan. 21, 2020, 1:41 p.m. UTC
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

Comments

Rafael J. Wysocki Jan. 21, 2020, 4:09 p.m. UTC | #1
On Tue, Jan 21, 2020 at 2:41 PM Sakari Ailus
<sakari.ailus@linux.intel.com> wrote:
>
> 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.

Well, if you say "has been defined", you need to provide a pointer to
the definition document (a specification of some sort or similar).

> +
> +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
>
Sakari Ailus Jan. 21, 2020, 4:18 p.m. UTC | #2
On Tue, Jan 21, 2020 at 05:09:44PM +0100, Rafael J. Wysocki wrote:
> On Tue, Jan 21, 2020 at 2:41 PM Sakari Ailus
> <sakari.ailus@linux.intel.com> wrote:
> >
> > 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.
> 
> Well, if you say "has been defined", you need to provide a pointer to
> the definition document (a specification of some sort or similar).

How about:

s/has been defined/is used/

> 
> > +
> > +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
> >
Rafael J. Wysocki Jan. 21, 2020, 4:56 p.m. UTC | #3
On Tue, Jan 21, 2020 at 5:19 PM Sakari Ailus
<sakari.ailus@linux.intel.com> wrote:
>
> On Tue, Jan 21, 2020 at 05:09:44PM +0100, Rafael J. Wysocki wrote:
> > On Tue, Jan 21, 2020 at 2:41 PM Sakari Ailus
> > <sakari.ailus@linux.intel.com> wrote:
> > >
> > > 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.
> >
> > Well, if you say "has been defined", you need to provide a pointer to
> > the definition document (a specification of some sort or similar).
>
> How about:
>
> s/has been defined/is used/

I would say "Linux recognizes the ... that can be used for this purpose."
Sakari Ailus Jan. 21, 2020, 4:58 p.m. UTC | #4
On Tue, Jan 21, 2020 at 05:56:39PM +0100, Rafael J. Wysocki wrote:
> On Tue, Jan 21, 2020 at 5:19 PM Sakari Ailus
> <sakari.ailus@linux.intel.com> wrote:
> >
> > On Tue, Jan 21, 2020 at 05:09:44PM +0100, Rafael J. Wysocki wrote:
> > > On Tue, Jan 21, 2020 at 2:41 PM Sakari Ailus
> > > <sakari.ailus@linux.intel.com> wrote:
> > > >
> > > > 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.
> > >
> > > Well, if you say "has been defined", you need to provide a pointer to
> > > the definition document (a specification of some sort or similar).
> >
> > How about:
> >
> > s/has been defined/is used/
> 
> I would say "Linux recognizes the ... that can be used for this purpose."

Ack; I'll use this in v5.

Patch
diff mbox series

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