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PCI: Improve pci_msi_supported() comments

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Improve pci_msi_supported() comments.

Signed-off-by: Brice Goglin <brice@myri.com>
Signed-off-by: Grant Grundler <grundler@parisc-linux.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Brice Goglin 2006-10-05 10:24:31 +02:00 committed by Greg Kroah-Hartman
parent 662a98fb8d
commit 0306ebfa3b
1 changed files with 9 additions and 7 deletions
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16
drivers/pci/msi.c
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@ -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;