PCI/PTM: Add pci_upstream_ptm() helper

PTM requires an unbroken path of PTM-supporting devices between the PTM
Root and the ultimate PTM Requester, but if a Switch supports PTM, only the
Upstream Port can have a PTM Capability; the Downstream Ports do not.

Previously we copied the PTM configuration from the Switch Upstream Port to
the Downstream Ports so dev->ptm_enabled for any device implied that all
the upstream devices support PTM.

Instead of making it look like Downstream Ports have their own PTM config,
add pci_upstream_ptm(), which returns the upstream device that has a PTM
Capability (either a Root Port or a Switch Upstream Port).

Link: https://lore.kernel.org/r/20220909202505.314195-3-helgaas@kernel.org
Tested-by: Rajvi Jingar <rajvi.jingar@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>

diff --git a/drivers/pci/pcie/ptm.c b/drivers/pci/pcie/ptm.c
index 85382c1..0df6cdf 100644 (file)
--- a/drivers/pci/pcie/ptm.c
+++ b/drivers/pci/pcie/ptm.c
@@ -76,6 +76,29 @@ void pci_restore_ptm_state(struct pci_dev *dev)
        pci_write_config_word(dev, ptm + PCI_PTM_CTRL, *cap);
 }
 
+/*
+ * If the next upstream device supports PTM, return it; otherwise return
+ * NULL.  PTM Messages are local, so both link partners must support it.
+ */
+static struct pci_dev *pci_upstream_ptm(struct pci_dev *dev)
+{
+       struct pci_dev *ups = pci_upstream_bridge(dev);
+
+       /*
+        * Switch Downstream Ports are not permitted to have a PTM
+        * capability; their PTM behavior is controlled by the Upstream
+        * Port (PCIe r5.0, sec 7.9.16), so if the upstream bridge is a
+        * Switch Downstream Port, look up one more level.
+        */
+       if (ups && pci_pcie_type(ups) == PCI_EXP_TYPE_DOWNSTREAM)
+               ups = pci_upstream_bridge(ups);
+
+       if (ups && ups->ptm_cap)
+               return ups;
+
+       return NULL;
+}
+
 void pci_ptm_init(struct pci_dev *dev)
 {
        u16 ptm;
@@ -95,19 +118,6 @@ void pci_ptm_init(struct pci_dev *dev)
             pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END))
                return;
 
-       /*
-        * Switch Downstream Ports are not permitted to have a PTM
-        * capability; their PTM behavior is controlled by the Upstream
-        * Port (PCIe r5.0, sec 7.9.16).
-        */
-       ups = pci_upstream_bridge(dev);
-       if (pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM &&
-           ups && ups->ptm_enabled) {
-               dev->ptm_granularity = ups->ptm_granularity;
-               dev->ptm_enabled = 1;
-               return;
-       }
-
        ptm = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_PTM);
        if (!ptm)
                return;
@@ -124,6 +134,7 @@ void pci_ptm_init(struct pci_dev *dev)
         * the spec recommendation (PCIe r3.1, sec 7.32.3), select the
         * furthest upstream Time Source as the PTM Root.
         */
+       ups = pci_upstream_ptm(dev);
        if (ups && ups->ptm_enabled) {
                ctrl = PCI_PTM_CTRL_ENABLE;
                if (ups->ptm_granularity == 0)
@@ -173,7 +184,7 @@ int pci_enable_ptm(struct pci_dev *dev, u8 *granularity)
         * associate the endpoint with a time source.
         */
        if (pci_pcie_type(dev) == PCI_EXP_TYPE_ENDPOINT) {
-               ups = pci_upstream_bridge(dev);
+               ups = pci_upstream_ptm(dev);
                if (!ups || !ups->ptm_enabled)
                        return -EINVAL;