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-rw-r--r--drivers/pci/msi.c16
1 files changed, 9 insertions, 7 deletions
diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index f9fdc54473c4..9fc9a34ef24a 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -627,22 +627,24 @@ static int msix_capability_init(struct pci_dev *dev,
* pci_msi_supported - check whether MSI may be enabled on device
* @dev: pointer to the pci_dev data structure of MSI device function
*
- * MSI must be globally enabled and supported by the device and its root
- * bus. But, the root bus is not easy to find since some architectures
- * have virtual busses on top of the PCI hierarchy (for instance the
- * hypertransport bus), while the actual bus where MSI must be supported
- * is below. So we test the MSI flag on all parent busses and assume
- * that no quirk will ever set the NO_MSI flag on a non-root bus.
+ * Look at global flags, the device itself, and its parent busses
+ * to return 0 if MSI are supported for the device.
**/
static
int pci_msi_supported(struct pci_dev * dev)
{
struct pci_bus *bus;
+ /* MSI must be globally enabled and supported by the device */
if (!pci_msi_enable || !dev || dev->no_msi)
return -EINVAL;
- /* check MSI flags of all parent busses */
+ /* Any bridge which does NOT route MSI transactions from it's
+ * secondary bus to it's primary bus must set NO_MSI flag on
+ * the secondary pci_bus.
+ * We expect only arch-specific PCI host bus controller driver
+ * or quirks for specific PCI bridges to be setting NO_MSI.
+ */
for (bus = dev->bus; bus; bus = bus->parent)
if (bus->bus_flags & PCI_BUS_FLAGS_NO_MSI)
return -EINVAL;