radeon: RFC speed cap detection on ppc64

[Lucas Kannebley Tavares]

The radeon driver does speed cap detection on the root PCI device for 
the maximum speed with which the adapter can communicate. On ppc64 
systems, however, the root device belongs to the Hypervisor, so the 
current code would case a null pointer dereference.

I propose to look for the outmost bus with a parent node and get speed 
caps from it, though I suppose the cleaner way would be to inspect all 
devices along the way and choose the smallest speed cap.

Does anyone have suggestions for this?

Thanks

--
--- 
/home/lucaskt/work/devdrivers/kernel/linux/drivers/gpu/drm/drm_pci.c 
2012-09-26 10:06:00.280549928 -0300
+++ drm_pci.c	2012-09-26 15:38:51.121786353 -0300
@@ -466,6 +466,19 @@
 }
 EXPORT_SYMBOL(drm_pci_exit);

+static struct pci_dev *drm_get_pcie_root_dev(struct pci_dev *dev)
+{
+	// Go up through all possible busses to get the info for the outmost bus
+	while (!pci_is_root_bus(dev->bus))
+		dev = dev->bus->parent->self;
+	
+	// In POWER architectures there's no PCI root device, so it should 
just read
+	// the caps from the device itself
+	if (dev->bus->self != NULL)
+		return dev->bus->self;
+	else
+		return dev;
+}
+
 int drm_pcie_get_speed_cap_mask(struct drm_device *dev, u32 *mask)
 {
 	struct pci_dev *root;
@@ -479,7 +492,7 @@
 	if (!pci_is_pcie(dev->pdev))
 		return -EINVAL;

-	root = dev->pdev->bus->self;
+	root = drm_get_pcie_root_dev(dev->pdev);

 	pos = pci_pcie_cap(root);
 	if (!pos)


--
Lucas Kannebley Tavares
Software Engineer
IBM Linux Technology Center

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