netdev - Re: [net-next-2.6 PATCH] e1000e: don't inadvertently re-set INTX

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Date:	Fri, 18 Jun 2010 14:14:42 -0700
From:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:	Dean Nelson <dnelson@...hat.com>
Cc:	netdev@...r.kernel.org, Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [net-next-2.6 PATCH] e1000e: don't inadvertently re-set 
	INTX_DISABLE

On Fri, Jun 18, 2010 at 13:36, Dean Nelson <dnelson@...hat.com> wrote:
> 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>
> CC: stable@...nel.org
>
> ---
>
> I forced the msi interrupt test to fail by commenting out the clearing
> of FLAG_MSI_TEST_FAILED in e1000_intr_msi_test().
>
>  drivers/net/e1000e/netdev.c |   13 +++++++++----
>  1 files changed, 9 insertions(+), 4 deletions(-)
>

Thanks Dean, I have added it to my queue.

Cheers,
Jeff
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