Add a "enable" sysfs attribute to the pci devices to allowuserspace (Xorg) to enable devices without doing foul direct access

[Arjan van de Ven]

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@xxxxxxxxxxxxxxx>
CC: Peter Jones <pjones@xxxxxxxxxx>
CC: Dave Airlie <airlied@xxxxxxxx>
---
 drivers/pci/pci-sysfs.c |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

Index: linux-2.6.17-rc2-enable/drivers/pci/pci-sysfs.c
===================================================================
--- linux-2.6.17-rc2-enable.orig/drivers/pci/pci-sysfs.c
+++ linux-2.6.17-rc2-enable/drivers/pci/pci-sysfs.c
@@ -43,6 +43,7 @@ pci_config_attr(subsystem_vendor, "0x%04
 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 +91,28 @@ static ssize_t modalias_show(struct devi
 		       (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);
+
+	if (!pdev)
+		return 1;
+
+	/* this can crash the machine when done on the "wrong" device */
+	if (!capable(CAP_SYS_ADMIN))
+		return 1;
+
+	if (*buf == '0')
+		pci_disable_device(pdev);
+
+	if (*buf == '1')
+		pci_enable_device(pdev);
+
+	return 1;
+}
+
 
 struct device_attribute pci_dev_attrs[] = {
 	__ATTR_RO(resource),
@@ -101,6 +124,7 @@ 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,
 };
 

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