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    SubjectRe: [PATCH v3 01/25] PCI: Add PCI_ERROR_RESPONSE and it's related definitions
    On Thursday 21 October 2021 20:37:26 Naveen Naidu wrote:
    > An MMIO read from a PCI device that doesn't exist or doesn't respond
    > causes a PCI error. There's no real data to return to satisfy the
    > CPU read, so most hardware fabricates ~0 data.
    >
    > Add a PCI_ERROR_RESPONSE definition for that and use it where
    > appropriate to make these checks consistent and easier to find.
    >
    > Also add helper definitions SET_PCI_ERROR_RESPONSE and
    > RESPONSE_IS_PCI_ERROR to make the code more readable.
    >
    > Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
    > Signed-off-by: Naveen Naidu <naveennaidu479@gmail.com>

    Reviewed-by: Pali Rohár <pali@kernel.org>

    > ---
    > include/linux/pci.h | 9 +++++++++
    > 1 file changed, 9 insertions(+)
    >
    > diff --git a/include/linux/pci.h b/include/linux/pci.h
    > index cd8aa6fce204..689c8277c584 100644
    > --- a/include/linux/pci.h
    > +++ b/include/linux/pci.h
    > @@ -154,6 +154,15 @@ enum pci_interrupt_pin {
    > /* The number of legacy PCI INTx interrupts */
    > #define PCI_NUM_INTX 4
    >
    > +/*
    > + * Reading from a device that doesn't respond typically returns ~0. A
    > + * successful read from a device may also return ~0, so you need additional
    > + * information to reliably identify errors.
    > + */
    > +#define PCI_ERROR_RESPONSE (~0ULL)
    > +#define SET_PCI_ERROR_RESPONSE(val) (*(val) = ((typeof(*(val))) PCI_ERROR_RESPONSE))
    > +#define RESPONSE_IS_PCI_ERROR(val) ((val) == ((typeof(val)) PCI_ERROR_RESPONSE))
    > +
    > /*
    > * pci_power_t values must match the bits in the Capabilities PME_Support
    > * and Control/Status PowerState fields in the Power Management capability.
    > --
    > 2.25.1
    >

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