PCI/PTM: Add pci_suspend_ptm() and pci_resume_ptm()

We disable PTM during suspend because that allows some Root Ports to enter
lower-power PM states, which means we also need to disable PTM for all
downstream devices.  Add pci_suspend_ptm() and pci_resume_ptm() for this
purpose.

pci_enable_ptm() and pci_disable_ptm() are for drivers to use to enable or
disable PTM.  They use dev->ptm_enabled to keep track of whether PTM should
be enabled.

pci_suspend_ptm() and pci_resume_ptm() are PCI core-internal functions to
temporarily disable PTM during suspend and (depending on dev->ptm_enabled)
re-enable PTM during resume.

Enable/disable/suspend/resume all use internal __pci_enable_ptm() and
__pci_disable_ptm() functions that only update the PTM Control register.
Outline:

  pci_enable_ptm(struct pci_dev *dev)
  {
     __pci_enable_ptm(dev);
     dev->ptm_enabled = 1;
     pci_ptm_info(dev);
  }

  pci_disable_ptm(struct pci_dev *dev)
  {
     if (dev->ptm_enabled) {
       __pci_disable_ptm(dev);
       dev->ptm_enabled = 0;
     }
  }

  pci_suspend_ptm(struct pci_dev *dev)
  {
     if (dev->ptm_enabled)
       __pci_disable_ptm(dev);
  }

  pci_resume_ptm(struct pci_dev *dev)
  {
     if (dev->ptm_enabled)
       __pci_enable_ptm(dev);
  }

Nothing currently calls pci_resume_ptm(); the suspend path saves the PTM
state before disabling PTM, so the PTM state restore in the resume path
implicitly re-enables it.  A future change will use pci_resume_ptm() to fix
some problems with this approach.

Link: https://lore.kernel.org/r/[email protected]
Tested-by: Rajvi Jingar <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Mika Westerberg <[email protected]>

Author: bjorn-helgaas

drivers/pci/pci.c

@@ -2714,7 +2714,7 @@ int pci_prepare_to_sleep(struct pci_dev *dev)
 	 * lower-power idle state as a whole.
 	 */
 	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
-		pci_disable_ptm(dev);
+		pci_suspend_ptm(dev);
 
 	pci_enable_wake(dev, target_state, wakeup);
 
@@ -2772,7 +2772,7 @@ int pci_finish_runtime_suspend(struct pci_dev *dev)
 	 * lower-power idle state as a whole.
 	 */
 	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
-		pci_disable_ptm(dev);
+		pci_suspend_ptm(dev);
 
 	__pci_enable_wake(dev, target_state, pci_dev_run_wake(dev));
 

drivers/pci/pci.h

@@ -507,11 +507,13 @@ static inline int pci_iov_bus_range(struct pci_bus *bus)
 #ifdef CONFIG_PCIE_PTM
 void pci_save_ptm_state(struct pci_dev *dev);
 void pci_restore_ptm_state(struct pci_dev *dev);
-void pci_disable_ptm(struct pci_dev *dev);
+void pci_suspend_ptm(struct pci_dev *dev);
+void pci_resume_ptm(struct pci_dev *dev);
 #else
 static inline void pci_save_ptm_state(struct pci_dev *dev) { }
 static inline void pci_restore_ptm_state(struct pci_dev *dev) { }
-static inline void pci_disable_ptm(struct pci_dev *dev) { }
+static inline void pci_suspend_ptm(struct pci_dev *dev) { }
+static inline void pci_resume_ptm(struct pci_dev *dev) { }
 #endif
 
 unsigned long pci_cardbus_resource_alignment(struct resource *);

drivers/pci/pcie/ptm.c

@@ -29,7 +29,7 @@ static void pci_ptm_info(struct pci_dev *dev)
 		 dev->ptm_root ? " (root)" : "", clock_desc);
 }
 
-void pci_disable_ptm(struct pci_dev *dev)
+static void __pci_disable_ptm(struct pci_dev *dev)
 {
 	u16 ptm = dev->ptm_cap;
 	u16 ctrl;
@@ -42,6 +42,21 @@ void pci_disable_ptm(struct pci_dev *dev)
 	pci_write_config_word(dev, ptm + PCI_PTM_CTRL, ctrl);
 }
 
+/**
+ * pci_disable_ptm() - Disable Precision Time Measurement
+ * @dev: PCI device
+ *
+ * Disable Precision Time Measurement for @dev.
+ */
+void pci_disable_ptm(struct pci_dev *dev)
+{
+	if (dev->ptm_enabled) {
+		__pci_disable_ptm(dev);
+		dev->ptm_enabled = 0;
+	}
+}
+EXPORT_SYMBOL(pci_disable_ptm);
+
 void pci_save_ptm_state(struct pci_dev *dev)
 {
 	u16 ptm = dev->ptm_cap;
@@ -151,18 +166,8 @@ void pci_ptm_init(struct pci_dev *dev)
 		pci_enable_ptm(dev, NULL);
 }
 
-/**
- * pci_enable_ptm() - Enable Precision Time Measurement
- * @dev: PCI device
- * @granularity: pointer to return granularity
- *
- * Enable Precision Time Measurement for @dev.  If successful and
- * @granularity is non-NULL, return the Effective Granularity.
- *
- * Return: zero if successful, or -EINVAL if @dev lacks a PTM Capability or
- * is not a PTM Root and lacks an upstream path of PTM-enabled devices.
- */
-int pci_enable_ptm(struct pci_dev *dev, u8 *granularity)
+/* Enable PTM in the Control register if possible */
+static int __pci_enable_ptm(struct pci_dev *dev)
 {
 	u16 ptm = dev->ptm_cap;
 	struct pci_dev *ups;
@@ -191,8 +196,29 @@ int pci_enable_ptm(struct pci_dev *dev, u8 *granularity)
 		ctrl |= PCI_PTM_CTRL_ROOT;
 
 	pci_write_config_dword(dev, ptm + PCI_PTM_CTRL, ctrl);
-	dev->ptm_enabled = 1;
+	return 0;
+}
 
+/**
+ * pci_enable_ptm() - Enable Precision Time Measurement
+ * @dev: PCI device
+ * @granularity: pointer to return granularity
+ *
+ * Enable Precision Time Measurement for @dev.  If successful and
+ * @granularity is non-NULL, return the Effective Granularity.
+ *
+ * Return: zero if successful, or -EINVAL if @dev lacks a PTM Capability or
+ * is not a PTM Root and lacks an upstream path of PTM-enabled devices.
+ */
+int pci_enable_ptm(struct pci_dev *dev, u8 *granularity)
+{
+	int rc;
+
+	rc = __pci_enable_ptm(dev);
+	if (rc)
+		return rc;
+
+	dev->ptm_enabled = 1;
 	pci_ptm_info(dev);
 
 	if (granularity)
@@ -201,6 +227,23 @@ int pci_enable_ptm(struct pci_dev *dev, u8 *granularity)
 }
 EXPORT_SYMBOL(pci_enable_ptm);
 
+/*
+ * Disable PTM, but preserve dev->ptm_enabled so we silently re-enable it on
+ * resume if necessary.
+ */
+void pci_suspend_ptm(struct pci_dev *dev)
+{
+	if (dev->ptm_enabled)
+		__pci_disable_ptm(dev);
+}
+
+/* If PTM was enabled before suspend, re-enable it when resuming */
+void pci_resume_ptm(struct pci_dev *dev)
+{
+	if (dev->ptm_enabled)
+		__pci_enable_ptm(dev);
+}
+
 bool pcie_ptm_enabled(struct pci_dev *dev)
 {
 	if (!dev)

include/linux/pci.h

@@ -1678,10 +1678,12 @@ bool pci_ats_disabled(void);
 
 #ifdef CONFIG_PCIE_PTM
 int pci_enable_ptm(struct pci_dev *dev, u8 *granularity);
+void pci_disable_ptm(struct pci_dev *dev);
 bool pcie_ptm_enabled(struct pci_dev *dev);
 #else
 static inline int pci_enable_ptm(struct pci_dev *dev, u8 *granularity)
 { return -EINVAL; }
+static inline void pci_disable_ptm(struct pci_dev *dev) { }
 static inline bool pcie_ptm_enabled(struct pci_dev *dev)
 { return false; }
 #endif