Re: [PATCH 2/4] PCI: Query platform firmware for device power state

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On Wednesday, August 31, 2016 08:15:18 AM Lukas Wunner wrote:
> Usually the most accurate way to determine a PCI device's power state is
> to read its PM Control & Status Register.  There are two cases however
> when this is not an option:  If the device doesn't have the PM
> capability at all, or if it is in D3cold.
> 
> In D3cold, reading from config space typically results in a fabricated
> "all ones" response.  But in D3hot, the two bits representing the power
> state in the PMCSR are *also* set to 1.  Thus D3hot and D3cold are not
> discernible by just reading the PMCSR.
> 
> A (supposedly) reliable way to detect D3cold is to query the platform
> firmware for its opinion on the device's power state.  To this end,
> add a ->get_power callback to struct pci_platform_pm_ops, and an
> implementation to acpi_pci_platform_pm.  (The only pci_platform_pm_ops
> existing so far).
> 
> Amend pci_update_current_state() to query the platform firmware before
> reading the PMCSR.
> 
> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
> ---
>  drivers/pci/pci-acpi.c | 23 +++++++++++++++++++++++
>  drivers/pci/pci.c      | 21 ++++++++++++++++-----
>  drivers/pci/pci.h      |  3 +++
>  3 files changed, 42 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> index 9a033e8..89f2707 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -452,6 +452,28 @@ static int acpi_pci_set_power_state(struct pci_dev *dev, pci_power_t state)
>  	return error;
>  }
>  
> +static pci_power_t acpi_pci_get_power_state(struct pci_dev *dev)
> +{
> +	struct acpi_device *adev = ACPI_COMPANION(&dev->dev);
> +	static const pci_power_t state_conv[] = {
> +		[ACPI_STATE_D0]      = PCI_D0,
> +		[ACPI_STATE_D1]      = PCI_D1,
> +		[ACPI_STATE_D2]      = PCI_D2,
> +		[ACPI_STATE_D3_HOT]  = PCI_D3hot,
> +		[ACPI_STATE_D3_COLD] = PCI_D3cold,
> +	};
> +	int state;

ACPI_STATE_D3_HOT and ACPI_STATE_D3_COLD were introduced in ACPI 4.0.  For
systems predating that, ACPI_STATE_D3_HOT is the deepest state returned by
acpi_device_get_power().

> +
> +	if (!adev || !acpi_device_power_manageable(adev))
> +		return PCI_UNKNOWN;
> +
> +	if (acpi_device_get_power(adev, &state) || state < ACPI_STATE_D0
> +						|| state > ACPI_STATE_D3_COLD)

If the device is power-manageable by ACPI (you've just checked that) and
acpi_device_get_power() returns success (0), the returned state is guaranteed
to be within the boundaries (if it isn't, there is a bug that needs to be fixed).

> +		return PCI_UNKNOWN;
> +
> +	return state_conv[state];
> +}
> +
>  static bool acpi_pci_can_wakeup(struct pci_dev *dev)
>  {
>  	struct acpi_device *adev = ACPI_COMPANION(&dev->dev);
> @@ -534,6 +556,7 @@ static bool acpi_pci_need_resume(struct pci_dev *dev)
>  static const struct pci_platform_pm_ops acpi_pci_platform_pm = {
>  	.is_manageable = acpi_pci_power_manageable,
>  	.set_state = acpi_pci_set_power_state,
> +	.get_state = acpi_pci_get_power_state,
>  	.choose_state = acpi_pci_choose_state,
>  	.sleep_wake = acpi_pci_sleep_wake,
>  	.run_wake = acpi_pci_run_wake,
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 72a9d3a..e52e3d4 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -552,8 +552,9 @@ static const struct pci_platform_pm_ops *pci_platform_pm;
>  
>  int pci_set_platform_pm(const struct pci_platform_pm_ops *ops)
>  {
> -	if (!ops->is_manageable || !ops->set_state || !ops->choose_state ||
> -	    !ops->sleep_wake || !ops->run_wake || !ops->need_resume)
> +	if (!ops->is_manageable || !ops->set_state  || !ops->get_state ||
> +	    !ops->choose_state  || !ops->sleep_wake || !ops->run_wake  ||
> +	    !ops->need_resume)
>  		return -EINVAL;
>  	pci_platform_pm = ops;
>  	return 0;
> @@ -570,6 +571,11 @@ static inline int platform_pci_set_power_state(struct pci_dev *dev,
>  	return pci_platform_pm ? pci_platform_pm->set_state(dev, t) : -ENOSYS;
>  }
>  
> +static inline pci_power_t platform_pci_get_power_state(struct pci_dev *dev)
> +{
> +	return pci_platform_pm ? pci_platform_pm->get_state(dev) : PCI_UNKNOWN;
> +}
> +
>  static inline pci_power_t platform_pci_choose_state(struct pci_dev *dev)
>  {
>  	return pci_platform_pm ?
> @@ -701,14 +707,19 @@ static int pci_raw_set_power_state(struct pci_dev *dev, pci_power_t state)
>  }
>  
>  /**
> - * pci_update_current_state - Read PCI power state of given device from its
> - *                            PCI PM registers and cache it
> + * pci_update_current_state - Read power state of given device and cache it
>   * @dev: PCI device to handle.
>   * @state: State to cache in case the device doesn't have the PM capability
> + *
> + * The power state is read from the PMCSR register, which however is
> + * inaccessible in D3cold. The platform firmware is therefore queried first
> + * to detect accessibility of the register.
>   */
>  void pci_update_current_state(struct pci_dev *dev, pci_power_t state)
>  {
> -	if (dev->pm_cap) {
> +	if (platform_pci_get_power_state(dev) == PCI_D3cold) {
> +		dev->current_state = PCI_D3cold;
> +	} else if (dev->pm_cap) {

Why exactly do you need to change this function?

>  		u16 pmcsr;
>  
>  		/*
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 9730c47..01d5206 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -42,6 +42,8 @@ int pci_probe_reset_function(struct pci_dev *dev);
>   *
>   * @set_state: invokes the platform firmware to set the device's power state
>   *
> + * @get_state: queries the platform firmware for a device's current power state
> + *
>   * @choose_state: returns PCI power state of given device preferred by the
>   *                platform; to be used during system-wide transitions from a
>   *                sleeping state to the working state and vice versa
> @@ -62,6 +64,7 @@ int pci_probe_reset_function(struct pci_dev *dev);
>  struct pci_platform_pm_ops {
>  	bool (*is_manageable)(struct pci_dev *dev);
>  	int (*set_state)(struct pci_dev *dev, pci_power_t state);
> +	pci_power_t (*get_state)(struct pci_dev *dev);
>  	pci_power_t (*choose_state)(struct pci_dev *dev);
>  	int (*sleep_wake)(struct pci_dev *dev, bool enable);
>  	int (*run_wake)(struct pci_dev *dev, bool enable);
> 

Thanks,
Rafael

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