[PATCH v3] pci-sysfs: Make PCI bridge attribute visible in sysfs

[Wong Vee Khee]

From: vwong <vee.khee.wong@xxxxxx>

 In this commit, we are exposing PCIe bridges attributes
 such as secondary bus number, subordinate bus number,
 max link speed and link width, current link speed and
 link width to sysfs located in /sys/bus/pci/devices/...

 Part of the reasons we are doing this rather than getting
 these information through parsing lspci is due to the fact
 that accessing PCIe link information via lspci require root
 privilege.

 This changes also allow clients to get PCIe bridges information
 easily because lspci list out all PCIe devices.

Signed-off-by: Wong Vee Khee <vee.khee.wong@xxxxxx>
Signed-off-by: Hui Chun Ong <hui.chun.ong@xxxxxx>
---
 drivers/pci/pci-sysfs.c       | 197 +++++++++++++++++++++++++++++++++++++++++-
 include/uapi/linux/pci_regs.h |   1 +
 2 files changed, 194 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 31e9961..a2ada91 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -154,6 +154,127 @@ static ssize_t resource_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RO(resource);
 
+static ssize_t max_link_speed_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	struct pci_dev *pci_dev = to_pci_dev(dev);
+	u32 linkcap;
+	int err;
+	const char *speed;
+
+	err = pcie_capability_read_dword(pci_dev, PCI_EXP_LNKCAP, &linkcap);
+
+	if (!err) {
+		switch (linkcap & PCI_EXP_LNKCAP_SLS) {
+		case PCI_EXP_LNKCAP_SLS_8_0GB:
+			speed = "8 GT/s";
+			break;
+		case PCI_EXP_LNKCAP_SLS_5_0GB:
+			speed = "5 GT/s";
+			break;
+		case PCI_EXP_LNKCAP_SLS_2_5GB:
+			speed = "2.5 GT/s";
+			break;
+		default:
+			speed = "Unknown speed";
+		}
+
+		return sprintf(buf, "%s\n", speed);
+	}
+
+	return -EINVAL;
+}
+static DEVICE_ATTR_RO(max_link_speed);
+
+static ssize_t max_link_width_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	struct pci_dev *pci_dev = to_pci_dev(dev);
+	u32 linkcap;
+	int err;
+
+	err = pcie_capability_read_dword(pci_dev, PCI_EXP_LNKCAP, &linkcap);
+
+	return err ? -EINVAL : sprintf(
+		buf, "%u\n", (linkcap & PCI_EXP_LNKCAP_MLW) >> 4);
+}
+static DEVICE_ATTR_RO(max_link_width);
+
+static ssize_t current_link_speed_show(struct device *dev,
+				       struct device_attribute *attr, char *buf)
+{
+	struct pci_dev *pci_dev = to_pci_dev(dev);
+	u16 linkstat;
+	int err;
+	const char *speed;
+
+	err = pcie_capability_read_word(pci_dev, PCI_EXP_LNKSTA, &linkstat);
+
+	if (!err) {
+		switch (linkstat & PCI_EXP_LNKSTA_CLS) {
+		case PCI_EXP_LNKSTA_CLS_8_0GB:
+			speed = "8 GT/s";
+			break;
+		case PCI_EXP_LNKSTA_CLS_5_0GB:
+			speed = "5 GT/s";
+			break;
+		case PCI_EXP_LNKSTA_CLS_2_5GB:
+			speed = "2.5 GT/s";
+			break;
+		default:
+			speed = "Unknown speed";
+		}
+
+		return sprintf(buf, "%s\n", speed);
+	}
+
+	return -EINVAL;
+}
+static DEVICE_ATTR_RO(current_link_speed);
+
+static ssize_t current_link_width_show(struct device *dev,
+				       struct device_attribute *attr, char *buf)
+{
+	struct pci_dev *pci_dev = to_pci_dev(dev);
+	u16 linkstat;
+	int err;
+
+	err = pcie_capability_read_word(pci_dev, PCI_EXP_LNKSTA, &linkstat);
+
+	return err ? -EINVAL : sprintf(
+		buf, "%u\n",
+		(linkstat & PCI_EXP_LNKSTA_NLW) >> PCI_EXP_LNKSTA_NLW_SHIFT);
+}
+static DEVICE_ATTR_RO(current_link_width);
+
+static ssize_t secondary_bus_number_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	struct pci_dev *pci_dev = to_pci_dev(dev);
+	u8 sec_bus;
+	int err;
+
+	err = pci_read_config_byte(pci_dev, PCI_SECONDARY_BUS, &sec_bus);
+
+	return err ? -EINVAL : sprintf(buf, "%u\n", sec_bus);
+}
+static DEVICE_ATTR_RO(secondary_bus_number);
+
+static ssize_t subordinate_bus_number_show(struct device *dev,
+					   struct device_attribute *attr,
+					   char *buf)
+{
+	struct pci_dev *pci_dev = to_pci_dev(dev);
+	u8 sub_bus;
+	int err;
+
+	err = pci_read_config_byte(pci_dev, PCI_SUBORDINATE_BUS, &sub_bus);
+
+	return err ? -EINVAL : sprintf(buf, "%u\n", sub_bus);
+}
+static DEVICE_ATTR_RO(subordinate_bus_number);
+
 static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
 			     char *buf)
 {
@@ -629,12 +750,17 @@ static struct attribute *pci_dev_attrs[] = {
 	NULL,
 };
 
-static const struct attribute_group pci_dev_group = {
-	.attrs = pci_dev_attrs,
+static struct attribute *pci_bridge_attrs[] = {
+	&dev_attr_subordinate_bus_number.attr,
+	&dev_attr_secondary_bus_number.attr,
+	NULL,
 };
 
-const struct attribute_group *pci_dev_groups[] = {
-	&pci_dev_group,
+static struct attribute *pcie_dev_attrs[] = {
+	&dev_attr_current_link_speed.attr,
+	&dev_attr_current_link_width.attr,
+	&dev_attr_max_link_width.attr,
+	&dev_attr_max_link_speed.attr,
 	NULL,
 };
 
@@ -1557,6 +1683,57 @@ static umode_t pci_dev_hp_attrs_are_visible(struct kobject *kobj,
 	return a->mode;
 }
 
+static umode_t pci_bridge_attrs_are_visible(struct kobject *kobj,
+					    struct attribute *a, int n)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct pci_dev *pdev = to_pci_dev(dev);
+
+	if (pci_is_bridge(pdev))
+		return a->mode;
+
+	return 0;
+}
+
+static umode_t pcie_dev_attrs_are_visible(struct kobject *kobj,
+					  struct attribute *a, int n)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct pci_dev *pdev = to_pci_dev(dev);
+
+	if (pci_is_pcie(pdev))
+		return a->mode;
+
+	return 0;
+}
+
+static const struct attribute_group pci_dev_group = {
+	.attrs = pci_dev_attrs,
+};
+
+const struct attribute_group *pci_dev_groups[] = {
+	&pci_dev_group,
+	NULL,
+};
+
+static const struct attribute_group pci_bridge_group = {
+	.attrs = pci_bridge_attrs,
+};
+
+const struct attribute_group *pci_bridge_groups[] = {
+	&pci_bridge_group,
+	NULL,
+};
+
+static const struct attribute_group pcie_dev_group = {
+	.attrs = pcie_dev_attrs,
+};
+
+const struct attribute_group *pcie_dev_groups[] = {
+	&pcie_dev_group,
+	NULL,
+};
+
 static struct attribute_group pci_dev_hp_attr_group = {
 	.attrs = pci_dev_hp_attrs,
 	.is_visible = pci_dev_hp_attrs_are_visible,
@@ -1592,12 +1769,24 @@ static struct attribute_group pci_dev_attr_group = {
 	.is_visible = pci_dev_attrs_are_visible,
 };
 
+static struct attribute_group pci_bridge_attr_group = {
+	.attrs = pci_bridge_attrs,
+	.is_visible = pci_bridge_attrs_are_visible,
+};
+
+static struct attribute_group pcie_dev_attr_group = {
+	.attrs = pcie_dev_attrs,
+	.is_visible = pcie_dev_attrs_are_visible,
+};
+
 static const struct attribute_group *pci_dev_attr_groups[] = {
 	&pci_dev_attr_group,
 	&pci_dev_hp_attr_group,
 #ifdef CONFIG_PCI_IOV
 	&sriov_dev_attr_group,
 #endif
+	&pci_bridge_attr_group,
+	&pcie_dev_attr_group,
 	NULL,
 };
 
diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
index d56bb00..c22d3eb 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -517,6 +517,7 @@
 #define  PCI_EXP_LNKCAP_SLS	0x0000000f /* Supported Link Speeds */
 #define  PCI_EXP_LNKCAP_SLS_2_5GB 0x00000001 /* LNKCAP2 SLS Vector bit 0 */
 #define  PCI_EXP_LNKCAP_SLS_5_0GB 0x00000002 /* LNKCAP2 SLS Vector bit 1 */
+#define  PCI_EXP_LNKCAP_SLS_8_0GB 0x00000003 /* LNKCAP2 SLS Vector bit 2 */
 #define  PCI_EXP_LNKCAP_MLW	0x000003f0 /* Maximum Link Width */
 #define  PCI_EXP_LNKCAP_ASPMS	0x00000c00 /* ASPM Support */
 #define  PCI_EXP_LNKCAP_L0SEL	0x00007000 /* L0s Exit Latency */
-- 
2.7.4