On Wed, Oct 02, 2013 at 12:29:04PM +0200, Alexander Gordeev wrote:

This series is against "next" branch in Bjorn's repo:
git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git

Currently pci_enable_msi_block() and pci_enable_msix() interfaces
return a error code in case of failure, 0 in case of success and a
positive value which indicates the number of MSI-X/MSI interrupts
that could have been allocated. The latter value should be passed
to a repeated call to the interfaces until a failure or success:


	for (i = 0; i < FOO_DRIVER_MAXIMUM_NVEC; i++)
		adapter->msix_entries[i].entry = i;

	while (nvec >= FOO_DRIVER_MINIMUM_NVEC) {
		rc = pci_enable_msix(adapter->pdev,
				     adapter->msix_entries, nvec);
		if (rc > 0)
			nvec = rc;
		else
			return rc;
	}

	return -ENOSPC;


This technique proved to be confusing and error-prone. Vast share
of device drivers simply fail to follow the described guidelines.

To clarify "Vast share of device drivers":

 - 58 drivers call pci_enable_msix()
 - 24 try a single allocation and then fallback to MSI/LSI
 - 19 use the loop style allocation as above
 - 14 try an allocation, and if it fails retry once
 - 1  incorrectly continues when pci_enable_msix() returns > 0

So 33 drivers (> 50%) successfully make use of the "confusing and
error-prone" return value.

Another 24 happily ignore it, which is also entirely fine.

And yes, one is buggy, so obviously the interface is too complex. Thanks
drivers/ntb/ntb_hw.c

cheers