RE: [PATCH] ACPI: PM: Fix regression in acpi_device_set_power()

[Mario.Limonciello]

> -----Original Message-----
> From: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
> Sent: Thursday, August 1, 2019 1:11 AM
> To: Rafael J. Wysocki
> Cc: Linux ACPI; Linux PM; Linux PCI; LKML; Mika Westerberg; Bjorn Helgaas;
> Limonciello, Mario
> Subject: Re: [PATCH] ACPI: PM: Fix regression in acpi_device_set_power()
> 
> 
> at 07:31, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
> 
> > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> >
> > Commit f850a48a0799 ("ACPI: PM: Allow transitions to D0 to occur in
> > special cases") overlooked the fact that acpi_power_transition() may
> > change the power.state value for the target device and if that
> > happens, it may confuse acpi_device_set_power() and cause it to
> > omit the _PS0 evaluation which on some systems is necessary to
> > change power states of devices from low-power to D0.
> >
> > Fix that by saving the current value of power.state for the
> > target device before passing it to acpi_power_transition() and
> > using the saved value in a subsequent check.
> >
> > Fixes: f850a48a0799 ("ACPI: PM: Allow transitions to D0 to occur in
> > special cases")
> > Reported-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
> > Reported-by: Mario Limonciello <mario.limonciello@xxxxxxxx>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> 
> Tested-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>

Tested-by: Mario Limonciello <mario.limonciello@xxxxxxxx>

> 
> > ---
> >  drivers/acpi/device_pm.c |    4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > Index: linux-pm/drivers/acpi/device_pm.c
> >
> ==============================================================
> =====
> > --- linux-pm.orig/drivers/acpi/device_pm.c
> > +++ linux-pm/drivers/acpi/device_pm.c
> > @@ -236,13 +236,15 @@ int acpi_device_set_power(struct acpi_de
> >  		if (device->power.flags.power_resources)
> >  			result = acpi_power_transition(device, target_state);
> >  	} else {
> > +		int cur_state = device->power.state;
> > +
> >  		if (device->power.flags.power_resources) {
> >  			result = acpi_power_transition(device, ACPI_STATE_D0);
> >  			if (result)
> >  				goto end;
> >  		}
> >
> > -		if (device->power.state == ACPI_STATE_D0) {
> > +		if (cur_state == ACPI_STATE_D0) {
> >  			int psc;
> >
> >  			/* Nothing to do here if _PSC is not present. */
>