From: Dean Nelson <dnelson@redhat.com>
Date: Wed, 30 Jun 2010 15:54:22 -0400
Subject: [net] e1000e: don't inadvertently re-set INTX_DISABLE
Message-id: <20100630155422.6314.66800.send-patch@localhost.localdomain>
Patchwork-id: 26642
O-Subject: [RHEL5.6 PATCH] e1000e: don't inadvertently re-set INTX_DISABLE
Bugzilla: 496127
RH-Acked-by: Andy Gospodarek <gospo@redhat.com>
RH-Acked-by: Prarit Bhargava <prarit@redhat.com>
RH-Acked-by: David S. Miller <davem@redhat.com>

Resolves RHBZ 496127.

Backport of net-next-2.6 commit 36f2407fe52c55566221f8c68c8fb808abffd2f5.

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.

Tested by myself on a number of Beaker systems by commenting out the clearing
of FLAG_MSI_TEST_FAILED in e1000_intr_msi_test(). The patch was also tested by
khali @linux-fr.org as reported in RHBZ 477774.

Brew build:
https://brewweb.devel.redhat.com/taskinfo?taskID=2561998


diff --git a/drivers/net/e1000e/netdev.c b/drivers/net/e1000e/netdev.c
index 5c858f3..43c8b89 100644
--- a/drivers/net/e1000e/netdev.c
+++ b/drivers/net/e1000e/netdev.c
@@ -3109,13 +3109,18 @@ static int e1000_test_msi(struct e1000_adapter *adapter)
 
 	/* 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)