Re: [PATCH v2 1/5] ACPI: Enable driver and firmware hints to control power at probe time

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Aug 26, 2019 at 11:31:08AM +0300, 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@linux.intel.com>
> ---
>  drivers/acpi/device_pm.c | 15 +++++++++++++--
>  include/linux/device.h   |  7 +++++++
>  2 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/device_pm.c b/drivers/acpi/device_pm.c
> index f616b16c1f0be..adcdf78ce4de8 100644
> --- a/drivers/acpi/device_pm.c
> +++ b/drivers/acpi/device_pm.c
> @@ -1276,7 +1276,12 @@ 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
> +#ifdef CONFIG_PM
> +		    && !(dev->driver->probe_low_power &&
> +			 device_property_present(dev, "probe-low-power"))
> +#endif
> +			) {
>  			/*
>  			 * If the device's PM QoS resume latency limit or flags
>  			 * have been exposed to user space, they have to be
> @@ -1324,7 +1329,13 @@ 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
> +#ifdef CONFIG_PM
> +	    && !(dev->driver->probe_low_power &&
> +		 device_property_present(dev, "probe-low-power"))
> +#endif
> +		) {
>  		acpi_dev_pm_full_power(adev);
>  		acpi_device_wakeup_disable(adev);
>  	}
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 6717adee33f01..4bc0ea4a3201a 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -248,6 +248,12 @@ enum probe_type {
>   * @owner:	The module owner.
>   * @mod_name:	Used for built-in modules.
>   * @suppress_bind_attrs: Disables bind/unbind via sysfs.
> + * @probe_low_power: The driver supports its probe function being called while
> + *		     the device is in a low power state, 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.
> + *		     This configuration has no effect if CONFIG_PM is disabled.
>   * @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.
> @@ -285,6 +291,7 @@ struct device_driver {
>  	const char		*mod_name;	/* used for built-in modules */
>  
>  	bool suppress_bind_attrs;	/* disables bind/unbind via sysfs */
> +	bool probe_low_power;

Ick, no, this should be a bus-specific thing to handle such messed up
hardware.  Why polute this in the driver core?

thanks,

greg k-h