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Date: Thu, 10 Oct 2013 19:17:18 -0400
From: Mark Lord <kernel@start.ca>
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To: Alexander Gordeev <agordeev@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH RFC 00/77] Re-design MSI/MSI-X interrupts enablement
 pattern
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Just to help us all understand "the loop" issue..

Here's an example of driver code which uses the existing MSI-X interfaces,
for a device which can work with either 16, 8, 4, 2, or 1 MSI-X interrupt.
This is from a new driver I'm working on right now:


static int xx_alloc_msix_irqs (struct xx_dev *dev, int nvec)
{
        xx_disable_all_irqs(dev);
        do {
                if (nvec < 2)
                        xx_prep_for_1_msix_vector(dev);
                else if (nvec < 4)
                        xx_prep_for_2_msix_vectors(dev);
                else if (nvec < 8)
                        xx_prep_for_4_msix_vectors(dev);
                else if (nvec < 16)
                        xx_prep_for_8_msix_vectors(dev);
                else
                        xx_prep_for_16_msix_vectors(dev);
                nvec = pci_enable_msix(dev->pdev, dev->irqs, dev->num_vectors);
        } while (nvec > 0);

        if (nvec) {
                kerr(dev->name, "pci_enable_msix() failed, err=%d", nvec);
                dev->num_vectors = 0;
                return nvec;
        }
        return 0;       /* success */
}