Re: [PATCH 1/5] ACPI: Enable driver and firmware hints to control power at probe time

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On Friday, May 10, 2019 12:09:26 PM CEST Sakari Ailus wrote:
> Allow drivers and firmware tell ACPI that there's no need to power on a
> device for probe. This requires both a hint from the firmware as well as
> an indication from a driver to leave the device off.
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> ---
>  drivers/acpi/device_pm.c | 9 +++++++--
>  include/linux/device.h   | 6 ++++++
>  2 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/device_pm.c b/drivers/acpi/device_pm.c
> index b859d75eaf9f6..ca2409a30d26d 100644
> --- a/drivers/acpi/device_pm.c
> +++ b/drivers/acpi/device_pm.c
> @@ -1225,7 +1225,9 @@ static void acpi_dev_pm_detach(struct device *dev, bool power_off)
>  	if (adev && dev->pm_domain == &acpi_general_pm_domain) {
>  		dev_pm_domain_set(dev, NULL);
>  		acpi_remove_pm_notifier(adev);
> -		if (power_off) {
> +		if (power_off &&
> +		    !(dev->driver->probe_powered_off &&
> +		      device_property_present(dev, "avoid-power-probe"))) {
>  			/*
>  			 * If the device's PM QoS resume latency limit or flags
>  			 * have been exposed to user space, they have to be
> @@ -1273,7 +1275,10 @@ int acpi_dev_pm_attach(struct device *dev, bool power_on)
>  
>  	acpi_add_pm_notifier(adev, dev, acpi_pm_notify_work_func);
>  	dev_pm_domain_set(dev, &acpi_general_pm_domain);
> -	if (power_on) {
> +
> +	if (power_on &&
> +	    !(dev->driver->probe_powered_off &&
> +	      device_property_present(dev, "avoid-power-probe"))) {
>  		acpi_dev_pm_full_power(adev);
>  		acpi_device_wakeup_disable(adev);
>  	}
> diff --git a/include/linux/device.h b/include/linux/device.h
> index e85264fb66161..2a459fd5b954a 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -245,6 +245,11 @@ enum probe_type {
>   * @owner:	The module owner.
>   * @mod_name:	Used for built-in modules.
>   * @suppress_bind_attrs: Disables bind/unbind via sysfs.
> + * @probe_powered_off: The driver supports its probe function being called while
> + *		       the device is powered off, independently of the expected
> + *		       behaviour on combination of a given bus and firmware
> + *		       interface etc. The driver is responsible for powering the
> + *		       device on using runtime PM in such case.
>   * @probe_type:	Type of the probe (synchronous or asynchronous) to use.
>   * @of_match_table: The open firmware table.
>   * @acpi_match_table: The ACPI match table.
> @@ -282,6 +287,7 @@ struct device_driver {
>  	const char		*mod_name;	/* used for built-in modules */
>  
>  	bool suppress_bind_attrs;	/* disables bind/unbind via sysfs */
> +	bool probe_powered_off;

This is a bit of a misnomer IMO, because it is not just about devices that are completely off.
>From the ACPI perspective that is about all devices not in D0, which may mean gated clocks
etc.

I would call it probe_low_power or similar and analogously in patch [2/5], and apart from this
I have no objections against this series, but I would suggest to CC the next iteration of it
to Greg K-H and the LKML as it touches the driver core.

>  	enum probe_type probe_type;
>  
>  	const struct of_device_id	*of_match_table;
> 







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