+/**
+ * pci_update_current_state - Read PCI power state of given device from its
+ * PCI PM registers and cache it
+ * @dev: PCI device to handle.
+ * @pm: PCI PM capability offset of the device.
+ */
+static void pci_update_current_state(struct pci_dev *dev, int pm)
+{
+ if (pm) {
+ u16 pmcsr;
+
+ pci_read_config_word(dev, pm + PCI_PM_CTRL, &pmcsr);
+ dev->current_state = (pmcsr & PCI_PM_CTRL_STATE_MASK);
+ }
+}
+
+/**
+ * pci_set_power_state - Set the power state of a PCI device
+ * @dev: PCI device to handle.
+ * @state: PCI power state (D0, D1, D2, D3hot) to put the device into.
+ *
+ * Transition a device to a new power state, using the platform formware and/or
+ * the device's PCI PM registers.
+ *
+ * RETURN VALUE:
+ * -EINVAL if the requested state is invalid.
+ * -EIO if device does not support PCI PM or its PM capabilities register has a
+ * wrong version, or device doesn't support the requested state.
+ * 0 if device already is in the requested state.
+ * 0 if device's power state has been successfully changed.
+ */
+int pci_set_power_state(struct pci_dev *dev, pci_power_t state)
+{
+ int pm, error;
+
+ /* bound the state we're entering */
+ if (state > PCI_D3hot)
+ state = PCI_D3hot;
+ else if (state < PCI_D0)
+ state = PCI_D0;
+ else if ((state == PCI_D1 || state == PCI_D2) && pci_no_d1d2(dev))
+ /*
+ * If the device or the parent bridge do not support PCI PM,
+ * ignore the request if we're doing anything other than putting
+ * it into D0 (which would only happen on boot).
+ */
+ return 0;
+
+ /* Find PCI PM capability in the list */
+ pm = pci_find_capability(dev, PCI_CAP_ID_PM);
+
+ if (state == PCI_D0 && platform_pci_power_manageable(dev)) {
+ /*
+ * Allow the platform to change the state, for example via ACPI
+ * _PR0, _PS0 and some such, but do not trust it.
+ */
+ int ret = platform_pci_set_power_state(dev, PCI_D0);
+ if (!ret)
+ pci_update_current_state(dev, pm);
+ }
+
+ error = pci_raw_set_power_state(dev, pm, state);
+
+ if (state > PCI_D0 && platform_pci_power_manageable(dev)) {
+ /* Allow the platform to finalize the transition */
+ int ret = platform_pci_set_power_state(dev, state);
+ if (!ret) {
+ pci_update_current_state(dev, pm);
+ error = 0;
+ }
+ }
+
+ return error;
+}
+