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From: Greg KH on 6 Aug 2010 15:20
2.6.32-stable review patch. If anyone has any objections, please let us know.

------------------

From: Dean Nelson <dnelson(a)redhat.com>

commit 36f2407fe52c55566221f8c68c8fb808abffd2f5 upstream.

Should e1000_test_msi() fail to see an msi interrupt, it attempts to
fallback to legacy INTx interrupts. But an error in the code may prevent
this from happening correctly.

Before calling e1000_test_msi_interrupt(), e1000_test_msi() disables SERR
by clearing the SERR bit from the just read PCI_COMMAND bits as it writes
them back out.

Upon return from calling e1000_test_msi_interrupt(), it re-enables SERR
by writing out the version of PCI_COMMAND it had previously read.

The problem with this is that e1000_test_msi_interrupt() calls
pci_disable_msi(), which eventually ends up in pci_intx(). And because
pci_intx() was called with enable set to 1, the INTX_DISABLE bit gets
cleared from PCI_COMMAND, which is what we want. But when we get back to
e1000_test_msi(), the INTX_DISABLE bit gets inadvertently re-set because
of the attempt by e1000_test_msi() to re-enable SERR.

The solution is to have e1000_test_msi() re-read the PCI_COMMAND bits as
part of its attempt to re-enable SERR.

During debugging/testing of this issue I found that not all the systems
I ran on had the SERR bit set to begin with. And on some of the systems
the same could be said for the INTX_DISABLE bit. Needless to say these
latter systems didn't have a problem falling back to legacy INTx
interrupts with the code as is.

Signed-off-by: Dean Nelson <dnelson(a)redhat.com>
Tested-by: Emil Tantilov <emil.s.tantilov(a)intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher(a)intel.com>
Signed-off-by: David S. Miller <davem(a)davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
drivers/net/e1000e/netdev.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

--- a/drivers/net/e1000e/netdev.c
+++ b/drivers/net/e1000e/netdev.c
@@ -3073,13 +3073,18 @@ static int e1000_test_msi(struct e1000_a

/* disable SERR in case the MSI write causes a master abort */
pci_read_config_word(adapter->pdev, PCI_COMMAND, &pci_cmd);
- pci_write_config_word(adapter->pdev, PCI_COMMAND,
- pci_cmd & ~PCI_COMMAND_SERR);
+ if (pci_cmd & PCI_COMMAND_SERR)
+ pci_write_config_word(adapter->pdev, PCI_COMMAND,
+ pci_cmd & ~PCI_COMMAND_SERR);

err = e1000_test_msi_interrupt(adapter);

- /* restore previous setting of command word */
- pci_write_config_word(adapter->pdev, PCI_COMMAND, pci_cmd);
+ /* re-enable SERR */
+ if (pci_cmd & PCI_COMMAND_SERR) {
+ pci_read_config_word(adapter->pdev, PCI_COMMAND, &pci_cmd);
+ pci_cmd |= PCI_COMMAND_SERR;
+ pci_write_config_word(adapter->pdev, PCI_COMMAND, pci_cmd);
+ }

/* success ! */
if (!err)


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