[PATCH V7 7/9] PCI/sysfs: Add a 10-Bit Tag sysfs file

Dongdong Liu
2021-08-04T13:49:30Z

PCIe spec 5.0 r1.0 section 2.2.6.2 says that if an Endpoint supports
sending Requests to other Endpoints (as opposed to host memory), the
Endpoint must not send 10-Bit Tag Requests to another given Endpoint
unless an implementation-specific mechanism determines that the Endpoint
supports 10-Bit Tag Completer capability. Add a 10bit_tag sysfs file,
write 0 to disable 10-Bit Tag Requester when the driver does not bind
the device if the peer device does not support the 10-Bit Tag Completer.
This will make P2P traffic safe. the 10bit_tag file content indicate
current 10-Bit Tag Requester Enable status.

Signed-off-by: Dongdong Liu <liudongdong3@huawei.com>
---
Documentation/ABI/testing/sysfs-bus-pci | 16 +++++++-
drivers/pci/pci-sysfs.c | 69 +++++++++++++++++++++++++++++++++
2 files changed, 84 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index 793cbb7..0e0c97d 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -139,7 +139,7 @@ Description:
binary file containing the Vital Product Data for the
device. It should follow the VPD format defined in
PCI Specification 2.1 or 2.2, but users should consider
- that some devices may have incorrectly formatted data.
+ that some devices may have incorrectly formatted data.
If the underlying VPD has a writable section then the
corresponding section of this file will be writable.

@@ -407,3 +407,17 @@ Description:

The file is writable if the PF is bound to a driver that
implements ->sriov_set_msix_vec_count().
+
+What: /sys/bus/pci/devices/.../10bit_tag
+Date: August 2021
+Contact: Dongdong Liu <liudongdong3@huawei.com>
+Description:
+ If a PCI device support 10-Bit Tag Requester, will create the
+ 10bit_tag sysfs file. The file is readable, the value
+ indicate current 10-Bit Tag Requester Enable.
+ 1 - enabled, 0 - disabled.
+
+ The file is also writeable, the value only accept by write 0
+ to disable 10-Bit Tag Requester when the driver does not bind
+ the deivce. The typical use case is for p2pdma when the peer
+ device does not support 10-BIT Tag Completer.
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 5d63df7..e93ce8b 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -306,6 +306,49 @@ static ssize_t enable_show(struct device *dev, struct device_attribute *attr,
}
static DEVICE_ATTR_RW(enable);

+static ssize_t pci_10bit_tag_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct pci_dev *pdev = to_pci_dev(dev);
+ bool enable;
+
+ if (kstrtobool(buf, &enable) < 0)
+ return -EINVAL;
+
+ if (enable != false )
+ return -EINVAL;
+
+ if (pdev->driver)
+ return -EBUSY;
+
+ pcie_capability_clear_word(pdev, PCI_EXP_DEVCTL2,
+ PCI_EXP_DEVCTL2_10BIT_TAG_REQ_EN);
+ pci_info(pdev, "disabled 10-Bit Tag Requester\n");
+
+ return count;
+}
+
+static ssize_t pci_10bit_tag_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct pci_dev *pdev = to_pci_dev(dev);
+ u16 ctl;
+ int ret;
+
+ ret = pcie_capability_read_word(pdev, PCI_EXP_DEVCTL2, &ctl);
+ if (ret)
+ return -EINVAL;
+
+ return sysfs_emit(buf, "%u\n",
+ !!(ctl & PCI_EXP_DEVCTL2_10BIT_TAG_REQ_EN));
+}
+
+static struct device_attribute dev_attr_10bit_tag = __ATTR(10bit_tag, 0600,
+ pci_10bit_tag_show,
+ pci_10bit_tag_store);
+
#ifdef CONFIG_NUMA
static ssize_t numa_node_store(struct device *dev,
struct device_attribute *attr, const char *buf,
@@ -635,6 +678,11 @@ static struct attribute *pcie_dev_attrs[] = {
NULL,
};

+static struct attribute *pcie_dev_10bit_tag_attrs[] = {
+ &dev_attr_10bit_tag.attr,
+ NULL,
+};
+
static struct attribute *pcibus_attrs[] = {
&dev_attr_bus_rescan.attr,
&dev_attr_cpuaffinity.attr,
@@ -1482,6 +1530,21 @@ static umode_t pcie_dev_attrs_are_visible(struct kobject *kobj,
return 0;
}

+static umode_t pcie_dev_10bit_tag_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 (pdev->is_virtfn)
+ return 0;
+
+ if (!(pdev->pcie_devcap2 & PCI_EXP_DEVCAP2_10BIT_TAG_REQ))
+ return 0;
+
+ return a->mode;
+}
+
static const struct attribute_group pci_dev_group = {
.attrs = pci_dev_attrs,
};
@@ -1521,6 +1584,11 @@ static const struct attribute_group pcie_dev_attr_group = {
.is_visible = pcie_dev_attrs_are_visible,
};

+static const struct attribute_group pcie_dev_10bit_tag_attr_group = {
+ .attrs = pcie_dev_10bit_tag_attrs,
+ .is_visible = pcie_dev_10bit_tag_attrs_are_visible,
+};
+
static const struct attribute_group *pci_dev_attr_groups[] = {
&pci_dev_attr_group,
&pci_dev_hp_attr_group,
@@ -1530,6 +1598,7 @@ static const struct attribute_group *pci_dev_attr_groups[] = {
#endif
&pci_bridge_attr_group,
&pcie_dev_attr_group,
+ &pcie_dev_10bit_tag_attr_group,
#ifdef CONFIG_PCIEAER
&aer_stats_attr_group,
#endif
--
2.7.4