On Mon, Jan 13, 2014 at 12:12:20PM -0700, Bjorn Helgaas wrote:
> > - nvec = rc;
> > - rc = pci_enable_msi_block(pdev, nvec);
> > - if (rc)
> > + if (pci_enable_msi_range(pdev, nvec, nvec) < 0)
> > goto intx;
> >
> > return nvec;
> >
> > single_msi:
> > - rc = pci_enable_msi(pdev);
> > - if (rc)
> > + if (pci_enable_msi_range(pdev, 1, 1) < 0)
>
> This part doesn't seem like an improvement. There are a hundred or so
> callers of pci_enable_msi() that only want a single MSI. Is there any
> benefit in changing them to use pci_enable_msi_range()?
In this particular case it reads better to me as one sees on the screen
pci_enable_msi_range(pdev, nvec, nvec) and pci_enable_msi_range(pdev, 1, 1)
calls. That allows to avoid switching in mind between negative-or-positive
return in the former call and negative-or-zero return from pci_enable_msi()
if we had it.
But in most cases when single MSI is enabled we do cause complication
with the patterns below (which I expect I am going be hated for ;) ):
- rc = pci_enable_msi(pdev);
- if (rc)
+ rc = pci_enable_msi_range(pdev, 1, 1);
+ if (rc < 0)
...
- rc = pci_enable_msi(pdev);
- if (!rc)
+ rc = pci_enable_msi_range(pdev, 1, 1);
+ if (rc > 0)
...
I think we have a tradeoff between the interface simplicity and code clarity.
What if we try to address both goals by making pci_enable_msi() a helper over
pci_enable_msi_range(pdev, 1, 1)? In this case the return value will match
negative-or-positive binary semantics while reads almost as good as it used to:
- rc = pci_enable_msi(pdev);
- if (rc)
+ rc = pci_enable_msi(pdev);
+ if (rc < 0)
...
- rc = pci_enable_msi(pdev);
- if (!rc)
+ rc = pci_enable_msi(pdev);
+ if (rc > 0)
...
The whole interface would not be inflated as well, with just:
diff --git a/Documentation/PCI/MSI-HOWTO.txt b/Documentation/PCI/MSI-HOWTO.txt
index a8d0100..fa0b27d 100644
--- a/Documentation/PCI/MSI-HOWTO.txt
+++ b/Documentation/PCI/MSI-HOWTO.txt
@@ -158,6 +158,9 @@ static int foo_driver_enable_single_msi(struct pci_dev
*pdev)
return pci_enable_msi_range(pdev, 1, 1);
}
+A helper function pci_enable_msi() could be used instead. Note, as just
+one MSI is requested it could return either a negative errno or 1.
+
4.2.2 pci_disable_msi
void pci_disable_msi(struct pci_dev *dev)
--
Regards,
Alexander Gordeev
agord...@redhat.com
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