[RFC PATCH v1 05/13] PCI/ASPM: Add pci_enable_link_state()

[Ilpo Järvinen]

pci_disable_link_state() lacks a symmetric pair. Some drivers want to
disable ASPM during certain phases of their operation but then
re-enable it later on. If pci_disable_link_state() is made for the
device, there is currently no way to re-enable the states that were
disabled.

Add pci_enable_link_state() to remove ASPM states from the state
disable mask.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
---
 drivers/pci/pcie/aspm.c | 44 +++++++++++++++++++++++++++++++++++++++++
 include/linux/pci.h     |  2 ++
 2 files changed, 46 insertions(+)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 4727f73a2d0d..aed59ab13c46 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -1165,6 +1165,50 @@ int pci_disable_link_state(struct pci_dev *pdev, int state)
 }
 EXPORT_SYMBOL(pci_disable_link_state);
 
+/**
+ * pci_enable_link_state - Re-enable device's link state
+ * @pdev: PCI device
+ * @state: ASPM link states to re-enable
+ *
+ * Enable device's link state that were previously disable so the link is
+ * allowed to enter the specific states. Note that if the BIOS didn't grant
+ * ASPM control to the OS, this does nothing because we can't touch the
+ * LNKCTL register.
+ *
+ * Return: 0 or a negative errno.
+ */
+int pci_enable_link_state(struct pci_dev *pdev, int state)
+{
+	struct pcie_link_state *link = pcie_aspm_get_link(pdev);
+
+	if (!link)
+		return -EINVAL;
+	/*
+	 * A driver requested that ASPM be disabled on this device, but
+	 * if we don't have permission to manage ASPM (e.g., on ACPI
+	 * systems we have to observe the FADT ACPI_FADT_NO_ASPM bit and
+	 * the _OSC method), we can't honor that request.  Windows has
+	 * a similar mechanism using "PciASPMOptOut", which is also
+	 * ignored in this situation.
+	 */
+	if (aspm_disabled) {
+		pci_warn(pdev, "can't enable ASPM; OS doesn't have ASPM control\n");
+		return -EPERM;
+	}
+
+	mutex_lock(&aspm_lock);
+	link->aspm_disable &= ~pci_link_state_mask(state);
+	pcie_config_aspm_link(link, policy_to_aspm_state(link));
+
+	if (state & PCIE_LINK_STATE_CLKPM)
+		link->clkpm_disable = 0;
+	pcie_set_clkpm(link, policy_to_clkpm_state(link));
+	mutex_unlock(&aspm_lock);
+
+	return 0;
+}
+EXPORT_SYMBOL(pci_enable_link_state);
+
 /**
  * pci_set_default_link_state - Set the default device link state
  * @pdev: PCI device
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 5597e97a086d..aec259d12ca0 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1777,11 +1777,13 @@ extern bool pcie_ports_native;
 int pci_disable_link_state(struct pci_dev *pdev, int state);
 int pci_disable_link_state_locked(struct pci_dev *pdev, int state);
 #ifdef CONFIG_PCIEASPM
+int pci_enable_link_state(struct pci_dev *pdev, int state);
 int pci_set_default_link_state(struct pci_dev *pdev, int state);
 void pcie_no_aspm(void);
 bool pcie_aspm_support_enabled(void);
 bool pcie_aspm_enabled(struct pci_dev *pdev);
 #else
+static inline int pci_enable_link_state(struct pci_dev *pdev, int state) { return -EOPNOTSUPP; }
 static inline int pci_set_default_link_state(struct pci_dev *pdev, int state)
 { return 0; }
 static inline void pcie_no_aspm(void) { }
-- 
2.30.2