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    SubjectRe: [PATCH v2 2/6] PCI/MSI: Factor out pci_get_msi_cap() interface
    On Thu, Sep 26, 2013 at 09:58:53AM +0100, David Laight wrote:
    > Would it be possible to do some kind of 2-stage allocation.
    > In the first pass the driver would pass a minimum and desired
    > number of MSI-X interrupts, but not actually be given any.

    Repeated calls to msi_enable_msi/msix() is what we are trying to avoid.

    > Interrupts could then be allocated after it is known how many
    > are required and how many are available.

    Yep, that what we are heading to. So basic pattern I see would be like this:

    int foo_driver_enable_msix(struct pci_dev *pdev, int nvec)
    {
    ...

    rc = pci_msix_table_size(pdev);
    if (rc < 0)
    return rc;

    nvec = min(nvec, rc);
    if (nvec < FOO_DRIVER_MINIMUM_NVEC)
    goto single_msi;

    for (i = 0; i < nvec; i++)
    entries[i].entry = i;

    rc = pci_enable_msix(pdev, entries, nvec);
    if (rc)
    goto single_msi;

    return 0;

    single_msi:
    ...

    }

    But this will break pSeries and we might end up with something like this:

    int foo_driver_enable_msix(struct pci_dev *pdev, int nvec)
    {
    ...

    rc = pci_msix_table_size(pdev);
    if (rc < 0)
    return rc;

    nvec = min(nvec, rc);
    if (nvec < FOO_DRIVER_MINIMUM_NVEC)
    goto single_msi;

    rc = pci_get_msix_limit(pdev, nvec);
    if (rc < 0)
    return rc;

    nvec = min(nvec, rc);
    if (nvec < FOO_DRIVER_MINIMUM_NVEC)
    goto single_msi;

    for (i = 0; i < nvec; i++)
    entries[i].entry = i;

    rc = pci_enable_msix(pdev, entries, nvec);
    if (rc)
    goto single_msi;

    return 0;

    single_msi:
    ...

    }

    > David

    --
    Regards,
    Alexander Gordeev
    agordeev@redhat.com


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