Re: [PATCH] ACPI: PM: Avoid using power resources if there are none for D0

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 6/4/20 7:22 PM, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> As recently reported, some platforms provide a list of power
> resources for device power state D3hot, through the _PR3 object,
> but they do not provide a list of power resources for device power
> state D0.
> 
> Among other things, this causes acpi_device_get_power() to return
> D3hot as the current state of the device in question if all of the
> D3hot power resources are "on", because it sees the power_resources
> flag set and calls acpi_power_get_inferred_state() which finds that
> D3hot is the shallowest power state with all of the associated power
> resources turned "on", so that's what it returns.  Moreover, that
> value takes precedence over the acpi_dev_pm_explicit_get() return
> value, because it means a deeper power state.  The device may very
> well be in D0 physically at that point, however.
> 
> Moreover, the presence of _PR3 without _PR0 for a given device
> means that only one D3-level power state can be supported by it.
> Namely, because there are no power resources to turn "off" when
> transitioning the device from D0 into D3cold (which should be
> supported since _PR3 is present), the evaluation of _PS3 should
> be sufficient to put it straight into D3cold, but this means that
> the effect of turning "on" the _PR3 power resources is unclear,
> so it is better to avoid doing that altogether.  Consequently,
> there is no practical way do distinguish D3cold from D3hot for
> the device in question and the power states of it can be labeled
> so that D3hot is the deepest supported one (and Linux assumes
> that putting a device into D3hot via ACPI may cause power to be
> removed from it anyway, for legacy reasons).
> 
> To work around the problem described above modify the ACPI
> enumeration of devices so that power resources are only used
> for device power management if the list of D0 power resources
> is not empty and make it mart D3cold as supported only if that
> is the case and the D3hot list of power resources is not empty
> too.
> 
> Fixes: ef85bdbec444 ("ACPI / scan: Consolidate extraction of power resources lists")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=205057
> Link: https://lore.kernel.org/linux-acpi/20200603194659.185757-1-hdegoede@redhat.com/
> Reported-by: Hans de Goede <hdegoede@redhat.com>
> Cc: 3.10+ <stable@vger.kernel.org> # 3.10+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Thank you.

I've tested this and I can confirm that it fixes the issue:

Tested-by: Hans de Goede <hdegoede@redhat.com>

I've also looked at the code and it looks good to me:

Reviewed-by: Hans de Goede <hdegoede@redhat.com>

Regards,

Hans





> ---
>   drivers/acpi/device_pm.c |    2 +-
>   drivers/acpi/scan.c      |   28 +++++++++++++++++++---------
>   2 files changed, 20 insertions(+), 10 deletions(-)
> 
> Index: linux-pm/drivers/acpi/scan.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/scan.c
> +++ linux-pm/drivers/acpi/scan.c
> @@ -919,12 +919,9 @@ static void acpi_bus_init_power_state(st
>   
>   		if (buffer.length && package
>   		    && package->type == ACPI_TYPE_PACKAGE
> -		    && package->package.count) {
> -			int err = acpi_extract_power_resources(package, 0,
> -							       &ps->resources);
> -			if (!err)
> -				device->power.flags.power_resources = 1;
> -		}
> +		    && package->package.count)
> +			acpi_extract_power_resources(package, 0, &ps->resources);
> +
>   		ACPI_FREE(buffer.pointer);
>   	}
>   
> @@ -971,14 +968,27 @@ static void acpi_bus_get_power_flags(str
>   		acpi_bus_init_power_state(device, i);
>   
>   	INIT_LIST_HEAD(&device->power.states[ACPI_STATE_D3_COLD].resources);
> -	if (!list_empty(&device->power.states[ACPI_STATE_D3_HOT].resources))
> -		device->power.states[ACPI_STATE_D3_COLD].flags.valid = 1;
>   
> -	/* Set defaults for D0 and D3hot states (always valid) */
> +	/* Set the defaults for D0 and D3hot (always supported). */
>   	device->power.states[ACPI_STATE_D0].flags.valid = 1;
>   	device->power.states[ACPI_STATE_D0].power = 100;
>   	device->power.states[ACPI_STATE_D3_HOT].flags.valid = 1;
>   
> +	/*
> +	 * Use power resources only if the D0 list of them is populated, because
> +	 * some platforms may provide _PR3 only to indicate D3cold support and
> +	 * in those cases the power resources list returned by it may be bogus.
> +	 */
> +	if (!list_empty(&device->power.states[ACPI_STATE_D0].resources)) {
> +		device->power.flags.power_resources = 1;
> +		/*
> +		 * D3cold is supported if the D3hot list of power resources is
> +		 * not empty.
> +		 */
> +		if (!list_empty(&device->power.states[ACPI_STATE_D3_HOT].resources))
> +			device->power.states[ACPI_STATE_D3_COLD].flags.valid = 1;
> +	}
> +
>   	if (acpi_bus_init_power(device))
>   		device->flags.power_manageable = 0;
>   }
> Index: linux-pm/drivers/acpi/device_pm.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/device_pm.c
> +++ linux-pm/drivers/acpi/device_pm.c
> @@ -186,7 +186,7 @@ int acpi_device_set_power(struct acpi_de
>   		 * possibly drop references to the power resources in use.
>   		 */
>   		state = ACPI_STATE_D3_HOT;
> -		/* If _PR3 is not available, use D3hot as the target state. */
> +		/* If D3cold is not supported, use D3hot as the target state. */
>   		if (!device->power.states[ACPI_STATE_D3_COLD].flags.valid)
>   			target_state = state;
>   	} else if (!device->power.states[state].flags.valid) {
> 
> 
>