On Wed, Dec 18, 2013 at 6:23 AM, Alexander Gordeev <agordeev@xxxxxxxxxx> wrote:
> On Tue, Dec 17, 2013 at 05:30:02PM -0700, Bjorn Helgaas wrote:
>
> Hi Bjorn,
>
> Thank you for the review!
>
> Sorry for a heavy skipping - I just wanted to focus on a principal
> moment in your suggestion and then go on with the original note.
>
>> I only see five users of pci_enable_msi_block() (nvme, ath10k, wil6210,
>> ipr, vfio); we can easily convert those to use pci_enable_msi_range() and
>> then remove pci_enable_msi_block().
>
>> It would be good if pci_enable_msix() could be implemented in terms of
>> pci_enable_msix_range(nvec, nvec), with a little extra glue to handle the
>> positive return values.
>
> So you want to get rid of the tri-state "low-level" pci_enable_msi_block()
> and pci_enable_msix(), right? I believe we can not do this, since we need
> to support a non-standard hardware which (a) can not be asked any arbitrary
> number of vectors within a range and (b) needs extra magic to enable MSI
> operation.
>
> I.e. below is a snippet from a real device driver Mark Lord has sent in a
> previous conversation:
>
> 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);
>
> The same probably could have been done with pci_enable_msix_range(nvec, nvec)
> call and checking for -ENOSPC errno, but IMO it would be less graceful and
> reliable, since -ENOSPC might come from anywhere.
>
> IOW, I believe we need to keep the door open for custom MSI-enablement (loop)
> implementations.
I think this can still be done even with pci_enable_msix_range().
Here's what I'm thinking, tell me where I'm going wrong:
rc = pci_enable_msix_range(dev->pdev, dev->irqs, 1, 16);
if (rc < 0) { /* error */ }
else { /* rc interrupts allocated */ }
If rc == 13 and the device can only use 8, the extra 5 would be
ignored and wasted.
If the waste is unacceptable, the driver can try this:
rc = pci_enable_msix_range(dev->pdev, dev->irqs, 16, 16);
if (rc < 0) {
rc = pci_enable_msix_range(dev->pdev, dev->irqs, 8, 8);
if (rc < 0) {
rc = pci_enable_msix_range(dev->pdev, dev->irqs, 4, 4);
...
}
if (rc < 0) { /* error, couldn't allocate *any* interrupts */
else { /* rc interrupts allocated (1, 2, 4, 8, or 16) */ }
Bjorn
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