[net-next-2.6,1/4] e1000e: don't inadvertently re-set INTX_DISABLE

From: Dean Nelson <dnelson@redhat.com>

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@redhat.com>
CC: stable@kernel.org
Tested-by: Emil Tantilov <emil.s.tantilov@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
---

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


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From: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Date: Tue, 29 Jun 2010 21:12:05 -0700

> From: Dean Nelson <dnelson@redhat.com>
> 
> 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.
...
> 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@redhat.com>
> CC: stable@kernel.org
> Tested-by: Emil Tantilov <emil.s.tantilov@intel.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

Applied.
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