[PATCH] PCI: Add a "enable" sysfs attribute to the pci devices to allow userspace (Xorg) to enable devices without doing foul direct access

This patch adds an "enable" sysfs attribute to each PCI device. When read it
shows the "enabled-ness" of the device, but you can write a "0" into it to
disable a device, and a "1" to enable it.

This later is needed for X and other cases where userspace wants to enable
the BARs on a device (typical example: to run the video bios on a secundary
head). Right now X does all this "by hand" via bitbanging, that's just evil.
This allows X to no longer do that but to just let the kernel do this.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
CC: Peter Jones <pjones@redhat.com>
Acked-by: Dave Airlie <airlied@linux.ie>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/pci/pci-sysfs.c

@@ -43,6 +43,7 @@ pci_config_attr(subsystem_vendor, "0x%04x\n");
 pci_config_attr(subsystem_device, "0x%04x\n");
 pci_config_attr(class, "0x%06x\n");
 pci_config_attr(irq, "%u\n");
+pci_config_attr(is_enabled, "%u\n");
 
 static ssize_t local_cpus_show(struct device *dev,
 			struct device_attribute *attr, char *buf)
@@ -90,6 +91,25 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
 		       (u8)(pci_dev->class >> 16), (u8)(pci_dev->class >> 8),
 		       (u8)(pci_dev->class));
 }
+static ssize_t
+is_enabled_store(struct device *dev, struct device_attribute *attr,
+		const char *buf, size_t count)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+
+	/* this can crash the machine when done on the "wrong" device */
+	if (!capable(CAP_SYS_ADMIN))
+		return count;
+
+	if (*buf == '0')
+		pci_disable_device(pdev);
+
+	if (*buf == '1')
+		pci_enable_device(pdev);
+
+	return count;
+}
+
 
 struct device_attribute pci_dev_attrs[] = {
 	__ATTR_RO(resource),
@@ -101,6 +121,7 @@ struct device_attribute pci_dev_attrs[] = {
 	__ATTR_RO(irq),
 	__ATTR_RO(local_cpus),
 	__ATTR_RO(modalias),
+	__ATTR(enable, 0600, is_enabled_show, is_enabled_store),
 	__ATTR_NULL,
 };