Date:	Fri, 15 May 2015 00:06:16 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Cc:	Aaron Lu <aaron.lu@...el.com>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Len Brown <len.brown@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Zhang Rui <rui.zhang@...el.com>
Subject: Re: [PATCH] ACPI / PM: Rework device power management to follow ACPI 6

On Thursday, May 07, 2015 12:37:13 AM Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> The ACPI 6 specification has made some changes in the device power
> management area.  In particular:
> 
>  * The D3hot power state is now supposed to be always available
>    (instead of D3cold) and D3cold is only regarded as valid if the
>    _PR3 object is present for the given device.
> 
>  * The required ordering of transitions into power states deeper than
>    D0 is now such that for a transition into state Dx the _PSx method
>    is supposed to be executed first, if present, and the states of
>    the power resources the device depends on are supposed to be
>    changed after that.
> 
>  * It is now explicitly forbidden to transition devices from
>    lower-power (deeper) into higher-power (shallower) power states
>    other than D0.
> 
> Those changes have been made so the specification reflects the
> Windows' device power management code that the vast majority of
> systems using ACPI is validated against.
> 
> To avoid artificial differences in ACPI device power management
> between Windows and Linux, modify the ACPI device power management
> code to follow the new specification.  Add comments explaining the
> code flow in some unclear places.
> 
> This only may affect some real corner cases in which the OS behavior
> expected by the firmware is different from the Windows one, but that's
> quite unlikely.  The transition ordering change affects transitions
> to D1 and D2 which are rarely used (if at all) and into D3hot and
> D3cold for devices actually having _PR3, but those are likely to
> be validated against Windows anyway.  The other changes may affect
> code calling acpi_device_get_power() or acpi_device_update_power()
> where ACPI_STATE_D3_HOT may be returned instead of ACPI_STATE_D3_COLD
> (that's why the ACPI fan driver needs to be updated too) and since
> transitions into ACPI_STATE_D3_HOT may remove power now, it is better
> to avoid this one in acpi_pm_device_sleep_state() if the "no power
> off" PM QoS flag is set.
> 
> The only existing user of acpi_device_can_poweroff() really cares
> about the case when _PR3 is present, so the change in that function
> should not cause any problems to happen too.
> 
> A plus is that PCI_D3hot can be mapped to ACPI_STATE_D3_HOT
> now and the compatibility with older systems should be covered
> automatically.
> 
> In any case, if any real problems result from this, it still will
> be better to follow the Windows' behavior (which now is reflected
> by the specification too) in general and handle the cases when it
> doesn't work via quirks.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

OK, so it looks like nobody has any comments, which in particular means
"no objections" to me.

I'm going to queue up this patch for 4.2, then.

> ---
>  drivers/acpi/device_pm.c |   97 ++++++++++++++++++++++++++++-------------------
>  drivers/acpi/fan.c       |    5 +-
>  drivers/acpi/power.c     |    3 -
>  drivers/acpi/scan.c      |   26 ++----------
>  drivers/pci/pci-acpi.c   |    2 
>  include/acpi/acpi_bus.h  |    3 -
>  6 files changed, 71 insertions(+), 65 deletions(-)
> 
> Index: linux-pm/drivers/acpi/power.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/power.c
> +++ linux-pm/drivers/acpi/power.c
> @@ -684,7 +684,8 @@ int acpi_power_get_inferred_state(struct
>  		}
>  	}
>  
> -	*state = ACPI_STATE_D3_COLD;
> +	*state = device->power.states[ACPI_STATE_D3_COLD].flags.valid ?
> +		ACPI_STATE_D3_COLD : ACPI_STATE_D3_HOT;
>  	return 0;
>  }
>  
> Index: linux-pm/include/acpi/acpi_bus.h
> ===================================================================
> --- linux-pm.orig/include/acpi/acpi_bus.h
> +++ linux-pm/include/acpi/acpi_bus.h
> @@ -272,7 +272,6 @@ struct acpi_device_power_flags {
>  struct acpi_device_power_state {
>  	struct {
>  		u8 valid:1;
> -		u8 os_accessible:1;
>  		u8 explicit_set:1;	/* _PSx present? */
>  		u8 reserved:6;
>  	} flags;
> @@ -602,7 +601,7 @@ static inline bool acpi_device_can_wakeu
>  
>  static inline bool acpi_device_can_poweroff(struct acpi_device *adev)
>  {
> -	return adev->power.states[ACPI_STATE_D3_COLD].flags.os_accessible;
> +	return adev->power.states[ACPI_STATE_D3_COLD].flags.valid;
>  }
>  
>  #else	/* CONFIG_ACPI */
> Index: linux-pm/drivers/acpi/scan.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/scan.c
> +++ linux-pm/drivers/acpi/scan.c
> @@ -1766,15 +1766,9 @@ static void acpi_bus_init_power_state(st
>  	if (acpi_has_method(device->handle, pathname))
>  		ps->flags.explicit_set = 1;
>  
> -	/*
> -	 * State is valid if there are means to put the device into it.
> -	 * D3hot is only valid if _PR3 present.
> -	 */
> -	if (!list_empty(&ps->resources)
> -	    || (ps->flags.explicit_set && state < ACPI_STATE_D3_HOT)) {
> +	/* State is valid if there are means to put the device into it. */
> +	if (!list_empty(&ps->resources) || ps->flags.explicit_set)
>  		ps->flags.valid = 1;
> -		ps->flags.os_accessible = 1;
> -	}
>  
>  	ps->power = -1;		/* Unknown - driver assigned */
>  	ps->latency = -1;	/* Unknown - driver assigned */
> @@ -1810,21 +1804,13 @@ 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 D3 states (always valid) */
> +	/* Set defaults for D0 and D3hot states (always valid) */
>  	device->power.states[ACPI_STATE_D0].flags.valid = 1;
>  	device->power.states[ACPI_STATE_D0].power = 100;
> -	device->power.states[ACPI_STATE_D3_COLD].flags.valid = 1;
> -	device->power.states[ACPI_STATE_D3_COLD].power = 0;
> -
> -	/* Set D3cold's explicit_set flag if _PS3 exists. */
> -	if (device->power.states[ACPI_STATE_D3_HOT].flags.explicit_set)
> -		device->power.states[ACPI_STATE_D3_COLD].flags.explicit_set = 1;
> -
> -	/* Presence of _PS3 or _PRx means we can put the device into D3 cold */
> -	if (device->power.states[ACPI_STATE_D3_HOT].flags.explicit_set ||
> -			device->power.flags.power_resources)
> -		device->power.states[ACPI_STATE_D3_COLD].flags.os_accessible = 1;
> +	device->power.states[ACPI_STATE_D3_HOT].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
> @@ -98,17 +98,16 @@ int acpi_device_get_power(struct acpi_de
>  
>  		/*
>  		 * The power resources settings may indicate a power state
> -		 * shallower than the actual power state of the device.
> +		 * shallower than the actual power state of the device, because
> +		 * the same power resources may be referenced by other devices.
>  		 *
> -		 * Moreover, on systems predating ACPI 4.0, if the device
> -		 * doesn't depend on any power resources and _PSC returns 3,
> -		 * that means "power off".  We need to maintain compatibility
> -		 * with those systems.
> +		 * For systems predating ACPI 4.0 we assume that D3hot is the
> +		 * deepest state that can be supported.
>  		 */
>  		if (psc > result && psc < ACPI_STATE_D3_COLD)
>  			result = psc;
>  		else if (result == ACPI_STATE_UNKNOWN)
> -			result = psc > ACPI_STATE_D2 ? ACPI_STATE_D3_COLD : psc;
> +			result = psc > ACPI_STATE_D2 ? ACPI_STATE_D3_HOT : psc;
>  	}
>  
>  	/*
> @@ -153,8 +152,8 @@ static int acpi_dev_pm_explicit_set(stru
>   */
>  int acpi_device_set_power(struct acpi_device *device, int state)
>  {
> +	int target_state = state;
>  	int result = 0;
> -	bool cut_power = false;
>  
>  	if (!device || !device->flags.power_manageable
>  	    || (state < ACPI_STATE_D0) || (state > ACPI_STATE_D3_COLD))
> @@ -169,11 +168,21 @@ int acpi_device_set_power(struct acpi_de
>  		return 0;
>  	}
>  
> -	if (!device->power.states[state].flags.valid) {
> +	if (state == ACPI_STATE_D3_COLD) {
> +		/*
> +		 * For transitions to D3cold we need to execute _PS3 and then
> +		 * 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 (!device->power.states[ACPI_STATE_D3_COLD].flags.valid)
> +			target_state = state;
> +	} else if (!device->power.states[state].flags.valid) {
>  		dev_warn(&device->dev, "Power state %s not supported\n",
>  			 acpi_power_state_string(state));
>  		return -ENODEV;
>  	}
> +
>  	if (!device->power.flags.ignore_parent &&
>  	    device->parent && (state < device->parent->power.state)) {
>  		dev_warn(&device->dev,
> @@ -183,39 +192,38 @@ int acpi_device_set_power(struct acpi_de
>  		return -ENODEV;
>  	}
>  
> -	/* For D3cold we should first transition into D3hot. */
> -	if (state == ACPI_STATE_D3_COLD
> -	    && device->power.states[ACPI_STATE_D3_COLD].flags.os_accessible) {
> -		state = ACPI_STATE_D3_HOT;
> -		cut_power = true;
> -	}
> -
> -	if (state < device->power.state && state != ACPI_STATE_D0
> -	    && device->power.state >= ACPI_STATE_D3_HOT) {
> -		dev_warn(&device->dev,
> -			 "Cannot transition to non-D0 state from D3\n");
> -		return -ENODEV;
> -	}
> -
>  	/*
>  	 * Transition Power
>  	 * ----------------
> -	 * In accordance with the ACPI specification first apply power (via
> -	 * power resources) and then evaluate _PSx.
> +	 * In accordance with ACPI 6, _PSx is executed before manipulating power
> +	 * resources, unless the target state is D0, in which case _PS0 is
> +	 * supposed to be executed after turning the power resources on.
>  	 */
> -	if (device->power.flags.power_resources) {
> -		result = acpi_power_transition(device, state);
> +	if (state > ACPI_STATE_D0) {
> +		/*
> +		 * According to ACPI 6, devices cannot go from lower-power
> +		 * (deeper) states to higher-power (shallower) states.
> +		 */
> +		if (state < device->power.state) {
> +			dev_warn(&device->dev, "Cannot transition from %s to %s\n",
> +				 acpi_power_state_string(device->power.state),
> +				 acpi_power_state_string(state));
> +			return -ENODEV;
> +		}
> +
> +		result = acpi_dev_pm_explicit_set(device, state);
>  		if (result)
>  			goto end;
> -	}
> -	result = acpi_dev_pm_explicit_set(device, state);
> -	if (result)
> -		goto end;
>  
> -	if (cut_power) {
> -		device->power.state = state;
> -		state = ACPI_STATE_D3_COLD;
> -		result = acpi_power_transition(device, state);
> +		if (device->power.flags.power_resources)
> +			result = acpi_power_transition(device, target_state);
> +	} else {
> +		if (device->power.flags.power_resources) {
> +			result = acpi_power_transition(device, ACPI_STATE_D0);
> +			if (result)
> +				goto end;
> +		}
> +		result = acpi_dev_pm_explicit_set(device, ACPI_STATE_D0);
>  	}
>  
>   end:
> @@ -264,13 +272,24 @@ int acpi_bus_init_power(struct acpi_devi
>  		return result;
>  
>  	if (state < ACPI_STATE_D3_COLD && device->power.flags.power_resources) {
> +		/* Reference count the power resources. */
>  		result = acpi_power_on_resources(device, state);
>  		if (result)
>  			return result;
>  
> -		result = acpi_dev_pm_explicit_set(device, state);
> -		if (result)
> -			return result;
> +		if (state == ACPI_STATE_D0) {
> +			/*
> +			 * If _PSC is not present and the state inferred from
> +			 * power resources appears to be D0, it still may be
> +			 * necessary to execute _PS0 at this point, because
> +			 * another device using the same power resources may
> +			 * have been put into D0 previously and that's why we
> +			 * see D0 here.
> +			 */
> +			result = acpi_dev_pm_explicit_set(device, state);
> +			if (result)
> +				return result;
> +		}
>  	} else if (state == ACPI_STATE_UNKNOWN) {
>  		/*
>  		 * No power resources and missing _PSC?  Cross fingers and make
> @@ -603,12 +622,12 @@ int acpi_pm_device_sleep_state(struct de
>  	if (d_max_in < ACPI_STATE_D0 || d_max_in > ACPI_STATE_D3_COLD)
>  		return -EINVAL;
>  
> -	if (d_max_in > ACPI_STATE_D3_HOT) {
> +	if (d_max_in > ACPI_STATE_D2) {
>  		enum pm_qos_flags_status stat;
>  
>  		stat = dev_pm_qos_flags(dev, PM_QOS_FLAG_NO_POWER_OFF);
>  		if (stat == PM_QOS_FLAGS_ALL)
> -			d_max_in = ACPI_STATE_D3_HOT;
> +			d_max_in = ACPI_STATE_D2;
>  	}
>  
>  	adev = ACPI_COMPANION(dev);
> Index: linux-pm/drivers/acpi/fan.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/fan.c
> +++ linux-pm/drivers/acpi/fan.c
> @@ -158,8 +158,9 @@ static int fan_get_state(struct acpi_dev
>  	if (result)
>  		return result;
>  
> -	*state = (acpi_state == ACPI_STATE_D3_COLD ? 0 :
> -		 (acpi_state == ACPI_STATE_D0 ? 1 : -1));
> +	*state = acpi_state == ACPI_STATE_D3_COLD
> +			|| acpi_state == ACPI_STATE_D3_HOT ?
> +		0 : (acpi_state == ACPI_STATE_D0 ? 1 : -1);
>  	return 0;
>  }
>  
> Index: linux-pm/drivers/pci/pci-acpi.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci-acpi.c
> +++ linux-pm/drivers/pci/pci-acpi.c
> @@ -420,7 +420,7 @@ static int acpi_pci_set_power_state(stru
>  		[PCI_D0] = ACPI_STATE_D0,
>  		[PCI_D1] = ACPI_STATE_D1,
>  		[PCI_D2] = ACPI_STATE_D2,
> -		[PCI_D3hot] = ACPI_STATE_D3_COLD,
> +		[PCI_D3hot] = ACPI_STATE_D3_HOT,
>  		[PCI_D3cold] = ACPI_STATE_D3_COLD,
>  	};
>  	int error = -EINVAL;
> 
> --
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-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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