PCI: Add Precision Time Measurement (PTM) support

Add Precision Time Measurement (PTM) support (see PCIe r3.1, sec 6.22).

Enable PTM on PTM Root devices and switch ports.  This does not enable PTM
on endpoints.

There currently are no PTM-capable devices on the market, but it is
expected to be supported by the Intel Apollo Lake platform.

[bhelgaas: complete rework]
Signed-off-by: Jonathan Yong <jonathan.yong@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

3 files changed, 82 insertions, 0 deletions

diff --git a/drivers/pci/pcie/Kconfig b/drivers/pci/pcie/Kconfig
index 7fcea75afa4c..7ce77635e5ad 100644
--- a/drivers/pci/pcie/Kconfig
+++ b/drivers/pci/pcie/Kconfig
@@ -92,3 +92,14 @@ config PCIE_DPC
           will be handled by the DPC driver.  If your system doesn't
           have this capability or you do not want to use this feature,
           it is safe to answer N.
+
+config PCIE_PTM
+        bool "PCIe Precision Time Measurement support"
+        default n
+        depends on PCIEPORTBUS
+        help
+          This enables PCI Express Precision Time Measurement (PTM)
+          support.
+
+          This is only useful if you have devices that support PTM, but it
+          is safe to enable even if you don't.
diff --git a/drivers/pci/pcie/Makefile b/drivers/pci/pcie/Makefile
index b24525b3dec1..36e35ea8fde7 100644
--- a/drivers/pci/pcie/Makefile
+++ b/drivers/pci/pcie/Makefile
@@ -16,3 +16,4 @@ obj-$(CONFIG_PCIEAER)		+= aer/
 obj-$(CONFIG_PCIE_PME) += pme.o
 
 obj-$(CONFIG_PCIE_DPC) += pcie-dpc.o
+obj-$(CONFIG_PCIE_PTM) += ptm.o
diff --git a/drivers/pci/pcie/ptm.c b/drivers/pci/pcie/ptm.c
new file mode 100644
index 000000000000..48eea4e65247
--- /dev/null
+++ b/drivers/pci/pcie/ptm.c
@@ -0,0 +1,70 @@
+/*
+ * PCI Express Precision Time Measurement
+ * Copyright (c) 2016, Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/pci.h>
+#include "../pci.h"
+
+static void pci_ptm_info(struct pci_dev *dev)
+{
+        dev_info(&dev->dev, "PTM enabled%s\n", dev->ptm_root ? " (root)" : "");
+}
+
+void pci_ptm_init(struct pci_dev *dev)
+{
+        int pos;
+        u32 cap, ctrl;
+        struct pci_dev *ups;
+
+        if (!pci_is_pcie(dev))
+                return;
+
+        pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_PTM);
+        if (!pos)
+                return;
+
+        /*
+         * Enable PTM only on interior devices (root ports, switch ports,
+         * etc.) on the assumption that it causes no link traffic until an
+         * endpoint enables it.
+         */
+        if ((pci_pcie_type(dev) == PCI_EXP_TYPE_ENDPOINT ||
+             pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END))
+                return;
+
+        pci_read_config_dword(dev, pos + PCI_PTM_CAP, &cap);
+
+        /*
+         * There's no point in enabling PTM unless it's enabled in the
+         * upstream device or this device can be a PTM Root itself.  Per
+         * the spec recommendation (PCIe r3.1, sec 7.32.3), select the
+         * furthest upstream Time Source as the PTM Root.
+         */
+        ups = pci_upstream_bridge(dev);
+        if (ups && ups->ptm_enabled) {
+                ctrl = PCI_PTM_CTRL_ENABLE;
+        } else {
+                if (cap & PCI_PTM_CAP_ROOT) {
+                        ctrl = PCI_PTM_CTRL_ENABLE | PCI_PTM_CTRL_ROOT;
+                        dev->ptm_root = 1;
+                } else
+                        return;
+        }
+
+        pci_write_config_dword(dev, pos + PCI_PTM_CTRL, ctrl);
+        dev->ptm_enabled = 1;
+
+        pci_ptm_info(dev);
+}