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    SubjectRe: [PATCH] msi: Immediately mask and unmask msi-x irqs.
    On Tue, Apr 03, 2007 at 01:41:49AM -0600, Eric W. Biederman wrote:
    > When we mask or unmask a msi-x irqs the writes may be posted because
    > we are writing to memory mapped region. This means the mask and
    > unmask don't happen immediately but at some unspecified time in the
    > future. Which is out of sync with how the mask/unmask logic work
    > for ioapic irqs.
    >
    > The practical result is that we get very subtle and hard to track down
    > irq migration bugs.
    >
    > This patch performs a read flush after writes to the MSI-X table for mask
    > and unmask operations. Since the SMP affinity is set while the interrupt
    > is masked, and since it's unmasked immediately after, no additional flushes
    > are required in the various affinity setting routines.

    set_msi_irq_affinity() is already doing read_msi_msg(). So the mask operation
    before this should atleast get flushed before we modify the irq destination
    information.

    With this patch however, unmask happens immediately.

    > diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
    > index ad33e01..435c195 100644
    > --- a/drivers/pci/msi.c
    > +++ b/drivers/pci/msi.c
    > @@ -94,6 +94,7 @@ static void msi_set_mask_bit(unsigned int irq, int flag)
    > int offset = entry->msi_attrib.entry_nr * PCI_MSIX_ENTRY_SIZE +
    > PCI_MSIX_ENTRY_VECTOR_CTRL_OFFSET;
    > writel(flag, entry->mask_base + offset);
    > + readl(entry->mask_base + offset);

    Don't we need the flush for the PCI_CAP_ID_MSI case aswell.

    thanks,
    suresh
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