Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Mon, 13 Jan 2020 11:41:12 +0100 | Subject | Re: [PATCH v3 2/5] ACPI: Add a convenience function to tell a device is suspended in probe |
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On Thu, Jan 9, 2020 at 4:44 PM Sakari Ailus <sakari.ailus@linux.intel.com> wrote: > > Add a convenience function to tell whether a device is suspended for probe > or remove, for busses where the custom is that drivers don't need to > resume devices in probe, or suspend them in their remove handlers. > > Returns false on non-ACPI systems. > > Suggested-by: Mika Westerberg <mika.westerberg@linux.intel.com> > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com> > --- > drivers/acpi/device_pm.c | 35 +++++++++++++++++++++++++++++++++++ > include/linux/acpi.h | 5 +++++ > 2 files changed, 40 insertions(+) > > diff --git a/drivers/acpi/device_pm.c b/drivers/acpi/device_pm.c > index 5e4a8860a9c0c..87393020276d8 100644 > --- a/drivers/acpi/device_pm.c > +++ b/drivers/acpi/device_pm.c > @@ -1348,4 +1348,39 @@ int acpi_dev_pm_attach(struct device *dev, bool power_on) > return 1; > } > EXPORT_SYMBOL_GPL(acpi_dev_pm_attach); > + > +/** > + * acpi_dev_low_power_state_probe - Tell if a device is in a low power state
"Check the current ACPI power state of a device."
> + * during probe
Why is this limited to probe?
The function actually checks whether or not the ACPI power state of the device is low-power at the call time (except that it is a bit racy with respect to _set_power(), so it may not work as expected if called in parallel with that one).
Maybe drop the "probe" part of the name (actually, I would call this function acpi_dev_state_low_power()) and add a paragraph about the potential race with _set_power() to the description?
> + * @dev: The device
"Physical device the ACPI power state of which to check".
> + * > + * Tell whether a given device is in a low power state during the driver's probe > + * or remove operation. > + * > + * Drivers of devices on certain busses such as I²C can generally assume (on > + * ACPI based systems) that the devices they control are powered on without > + * driver having to do anything about it. Using struct > + * device_driver.probe_low_power and "probe-low-power" property, this can be > + * negated and the driver has full control of the device power management.
The above information belongs somewhere else in my view.
> + * Always returns false on non-ACPI based systems. True is returned on ACPI
"On a system without ACPI, return false. On a system with ACPI, return true if the current ACPI power state of the device is not D0, or false otherwise.
Note that the power state of a device is not well-defined after it has been passed to acpi_device_set_power() and before that function returns, so it is not valid to ask for the ACPI power state of the device in that time frame."
> + * based systems iff the device is in a low power state during probe or remove. > + */ > +bool acpi_dev_low_power_state_probe(struct device *dev) > +{ > + int power_state; > + int ret; > + > + if (!is_acpi_device_node(dev_fwnode(dev))) > + return false;
This is (at least) inefficient, because the same check is repeated by ACPI_COMPANION().
If you really want to print the message, it is better to do something like
struct acpi_device *adev = ACPI_COMPANION(dev);
if (!adev) return false;
ret = acpi_device_get_power(adev, &power_state);
> + > + ret = acpi_device_get_power(ACPI_COMPANION(dev), &power_state); > + if (ret) { > + dev_warn(dev, "Cannot obtain power state (%d)\n", ret);
And the log level of this message is way too high IMO.
This means a firmware bug AFAICS and so after seeing it once on a given system it becomes noise. I'd use pr_debug() to print it.
> + return false; > + } > + > + return power_state != ACPI_STATE_D0; > +} > +EXPORT_SYMBOL_GPL(acpi_dev_low_power_state_probe); > + > #endif /* CONFIG_PM */
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