PCI/MSI: Add "msi_bus" sysfs MSI/MSI-X control for endpoints

The "msi_bus" sysfs file for bridges sets a bus flag to allow or disallow
future driver requests for MSI or MSI-X.  Previously, the sysfs file
existed for endpoints but did nothing.

Add "msi_bus" support for endpoints, so an administrator can prevent the
use of MSI and MSI-X for individual devices.

Note that as for bridges, these changes only affect future driver requests
for MSI or MSI-X, so drivers may need to be reloaded.

Add documentation for the "msi_bus" sysfs file.

[bhelgaas: changelog, comments, add "subordinate", add endpoint printk,
rework bus_flags setting, make bus_flags printk unconditional]
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index 6615fda..ee6c040 100644 (file)
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -65,6 +65,16 @@ Description:
                force a rescan of all PCI buses in the system, and
                re-discover previously removed devices.
 
+What:          /sys/bus/pci/devices/.../msi_bus
+Date:          September 2014
+Contact:       Linux PCI developers <linux-pci@vger.kernel.org>
+Description:
+               Writing a zero value to this attribute disallows MSI and
+               MSI-X for any future drivers of the device.  If the device
+               is a bridge, MSI and MSI-X will be disallowed for future
+               drivers of all child devices under the bridge.  Drivers
+               must be reloaded for the new setting to take effect.
+
 What:          /sys/bus/pci/devices/.../msi_irqs/
 Date:          September, 2011
 Contact:       Neil Horman <nhorman@tuxdriver.com>

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 9ff0a90..dbf63e2 100644 (file)
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -250,46 +250,45 @@ static ssize_t msi_bus_show(struct device *dev, struct device_attribute *attr,
                            char *buf)
 {
        struct pci_dev *pdev = to_pci_dev(dev);
+       struct pci_bus *subordinate = pdev->subordinate;
 
-       if (!pdev->subordinate)
-               return 0;
-
-       return sprintf(buf, "%u\n",
-                      !(pdev->subordinate->bus_flags & PCI_BUS_FLAGS_NO_MSI));
+       return sprintf(buf, "%u\n", subordinate ?
+                      !(subordinate->bus_flags & PCI_BUS_FLAGS_NO_MSI)
+                          : !pdev->no_msi);
 }
 
 static ssize_t msi_bus_store(struct device *dev, struct device_attribute *attr,
                             const char *buf, size_t count)
 {
        struct pci_dev *pdev = to_pci_dev(dev);
+       struct pci_bus *subordinate = pdev->subordinate;
        unsigned long val;
 
        if (kstrtoul(buf, 0, &val) < 0)
                return -EINVAL;
 
-       /*
-        * Bad things may happen if the no_msi flag is changed
-        * while drivers are loaded.
-        */
        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;
 
        /*
-        * Maybe devices without subordinate buses shouldn't have this
-        * attribute in the first place?
+        * "no_msi" and "bus_flags" only affect what happens when a driver
+        * requests MSI or MSI-X.  They don't affect any drivers that have
+        * already requested MSI or MSI-X.
         */
-       if (!pdev->subordinate)
+       if (!subordinate) {
+               pdev->no_msi = !val;
+               dev_info(&pdev->dev, "MSI/MSI-X %s for future drivers\n",
+                        val ? "allowed" : "disallowed");
                return count;
-
-       /* Is the flag going to change, or keep the value it already had? */
-       if (!(pdev->subordinate->bus_flags & PCI_BUS_FLAGS_NO_MSI) ^
-           !!val) {
-               pdev->subordinate->bus_flags ^= PCI_BUS_FLAGS_NO_MSI;
-
-               dev_warn(&pdev->dev, "forced subordinate bus to%s support MSI, bad things could happen\n",
-                        val ? "" : " not");
        }
 
+       if (val)
+               subordinate->bus_flags &= ~PCI_BUS_FLAGS_NO_MSI;
+       else
+               subordinate->bus_flags |= PCI_BUS_FLAGS_NO_MSI;
+
+       dev_info(&subordinate->dev, "MSI/MSI-X %s for future drivers of devices on this bus\n",
+                val ? "allowed" : "disallowed");
        return count;
 }
 static DEVICE_ATTR_RW(msi_bus);