linux-kernel - [11/36] e1000e: dont inadvertently re-set INTX

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Message-Id: <20100806192115.403787611@clark.site>
Date:	Fri, 06 Aug 2010 12:19:52 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Dean Nelson <dnelson@...hat.com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [11/36] e1000e: dont inadvertently re-set INTX_DISABLE

2.6.34-stable review patch.  If anyone has any objections, please let us know.

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

From: Dean Nelson <dnelson@...hat.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@...hat.com>
Tested-by: Emil Tantilov <emil.s.tantilov@...el.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.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
@@ -3041,13 +3041,18 @@ 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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