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    SubjectRe: [RFC] disable PCIE 'Enable No Snoop' bit by default
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    From: Matthew Wilcox <matthew@wil.cx>
    Date: Thu, 6 Sep 2007 05:57:31 -0600

    > I'm not sure your analysis is correct. Here's what my draft copy of
    > the pcie 2.0 spec says:
    >
    > Enble No Snoop ­ If this bit is Set, the Function is permitted to
    > Set the No Snoop bit in the Requester Attributes of transactions it
    > initiates that do not require hardware enforced cache coherency (see
    > Section 2.2.6.5). Note that setting this bit to 1b should not cause
    > a Function to Set the No Snoop attribute on all transactions that it
    > initiates. Even when this bit is Set, a Function is only permitted
    > to Set the No Snoop attribute on a transaction when it can guarantee
    > that the address of the transaction is not stored in any cache in
    > the system. This bit permitted to be hardwired to 0b if a Function
    > would never Set the No Snoop attribute in transactions it initiates.
    > Default value of this bit is 1b.
    >
    > That implies that devices are only allowed to set it when it's safe to
    > do so ... and we don't need to turn it off.

    This is my understanding of this area of PCI-E as well, and I
    also agree that therefore we should not turn this bit off.

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