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    Subject[PATCH RFC 06/77] PCI/MSI: Factor out pci_get_msi_cap() interface
    Date
    This update is needed to facilitate a forthcoming re-design
    MSI/MSI-X interrupts enabling pattern.

    Device drivers will use this interface to obtain maximum number
    of MSI interrupts the device supports and use that value in the
    following call to pci_enable_msi_block() interface.

    Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
    ---
    Documentation/PCI/MSI-HOWTO.txt | 15 +++++++++++++++
    drivers/pci/msi.c | 33 +++++++++++++++++++++------------
    include/linux/pci.h | 6 ++++++
    3 files changed, 42 insertions(+), 12 deletions(-)

    diff --git a/Documentation/PCI/MSI-HOWTO.txt b/Documentation/PCI/MSI-HOWTO.txt
    index 35b2d64..1f37ce2 100644
    --- a/Documentation/PCI/MSI-HOWTO.txt
    +++ b/Documentation/PCI/MSI-HOWTO.txt
    @@ -169,6 +169,21 @@ on any interrupt for which it previously called request_irq().
    Failure to do so results in a BUG_ON(), leaving the device with
    MSI enabled and thus leaking its vector.

    +4.2.5 pci_get_msi_cap
    +
    +int pci_get_msi_cap(struct pci_dev *dev)
    +
    +This function could be used to retrieve the number of MSI vectors the
    +device requested (via the Multiple Message Capable register). The MSI
    +specification only allows the returned value to be a power of two,
    +up to a maximum of 2^5 (32).
    +
    +If this function returns a negative number, it indicates the device is
    +not capable of sending MSIs.
    +
    +If this function returns a positive number, it indicates the maximum
    +number of MSI interrupt vectors that could be allocated.
    +
    4.3 Using MSI-X

    The MSI-X capability is much more flexible than the MSI capability.
    diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
    index 875c353..ca59bfc 100644
    --- a/drivers/pci/msi.c
    +++ b/drivers/pci/msi.c
    @@ -812,6 +812,21 @@ static int pci_msi_check_device(struct pci_dev *dev, int nvec, int type)
    return 0;
    }

    +int pci_get_msi_cap(struct pci_dev *dev)
    +{
    + int ret;
    + u16 msgctl;
    +
    + if (!dev->msi_cap)
    + return -EINVAL;
    +
    + pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &msgctl);
    + ret = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
    +
    + return ret;
    +}
    +EXPORT_SYMBOL(pci_get_msi_cap);
    +
    /**
    * pci_enable_msi_block - configure device's MSI capability structure
    * @dev: device to configure
    @@ -828,13 +843,10 @@ static int pci_msi_check_device(struct pci_dev *dev, int nvec, int type)
    int pci_enable_msi_block(struct pci_dev *dev, unsigned int nvec)
    {
    int status, maxvec;
    - u16 msgctl;

    - if (!dev->msi_cap)
    - return -EINVAL;
    -
    - pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &msgctl);
    - maxvec = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
    + maxvec = pci_get_msi_cap(dev);
    + if (maxvec < 0)
    + return maxvec;
    if (nvec > maxvec)
    return maxvec;

    @@ -859,13 +871,10 @@ EXPORT_SYMBOL(pci_enable_msi_block);
    int pci_enable_msi_block_auto(struct pci_dev *dev, unsigned int *maxvec)
    {
    int ret, nvec;
    - u16 msgctl;

    - if (!dev->msi_cap)
    - return -EINVAL;
    -
    - pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &msgctl);
    - ret = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
    + ret = pci_get_msi_cap(dev);
    + if (ret < 0)
    + return ret;

    if (maxvec)
    *maxvec = ret;
    diff --git a/include/linux/pci.h b/include/linux/pci.h
    index da172f9..2fa92ef 100644
    --- a/include/linux/pci.h
    +++ b/include/linux/pci.h
    @@ -1144,6 +1144,11 @@ struct msix_entry {


    #ifndef CONFIG_PCI_MSI
    +static inline int pci_get_msi_cap(struct pci_dev *dev)
    +{
    + return -1;
    +}
    +
    static inline int pci_enable_msi_block(struct pci_dev *dev, unsigned int nvec)
    {
    return -1;
    @@ -1185,6 +1190,7 @@ static inline int pci_msi_enabled(void)
    return 0;
    }
    #else
    +int pci_get_msi_cap(struct pci_dev *dev);
    int pci_enable_msi_block(struct pci_dev *dev, unsigned int nvec);
    int pci_enable_msi_block_auto(struct pci_dev *dev, unsigned int *maxvec);
    void pci_msi_shutdown(struct pci_dev *dev);
    --
    1.7.7.6


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