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

As proof of the "only a bus-specific thing", why is probe_low_power even
needed?  Why not just always trigger off of this crazy device_property?
That makes the driver changes less.

Also, is this #ifdef really needed?

thanks,

greg k-h