From: Alexander Gordeev <agordeev@redhat.com>
To: Bjorn Helgaas <bhelgaas@google.com>
Cc: linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>,
linux-ide@vger.kernel.org, linux-pci@vger.kernel.org
Subject: Re: [PATCH 3/7] ahci: Use new interfaces for MSI/MSI-X enablement
Date: Tue, 14 Jan 2014 09:50:40 +0100 [thread overview]
Message-ID: <20140114085040.GA6873@dhcp-26-207.brq.redhat.com> (raw)
In-Reply-To: <20140113191220.GA6525@google.com>
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
agordeev@redhat.com
next prev parent reply other threads:[~2014-01-14 8:48 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-07 18:05 [PATCH 0/7] Phase out pci_enable_msi_block() Alexander Gordeev
2014-01-07 18:05 ` [PATCH 1/7] ipr: Do not call pci_disable_msi/msix() if pci_enable_msi/msix() failed Alexander Gordeev
2014-01-07 18:05 ` [PATCH 2/7] ipr: Use new interfaces for MSI/MSI-X enablement Alexander Gordeev
2014-01-07 18:05 ` [PATCH 3/7] ahci: " Alexander Gordeev
2014-01-13 19:12 ` Bjorn Helgaas
2014-01-14 8:50 ` Alexander Gordeev [this message]
2014-01-14 8:54 ` Alexander Gordeev
2014-01-14 17:31 ` Bjorn Helgaas
2014-01-07 18:05 ` [PATCH 4/7] nvme: " Alexander Gordeev
2014-01-07 18:05 ` [PATCH 5/7] vfio: " Alexander Gordeev
2014-01-07 18:34 ` Alex Williamson
2014-01-08 7:42 ` Alexander Gordeev
2014-01-08 7:57 ` [PATCH v2 " Alexander Gordeev
2014-01-08 13:45 ` Alex Williamson
2014-01-10 7:42 ` [PATCH v3 " Alexander Gordeev
2014-01-10 15:45 ` Alex Williamson
2014-01-07 18:05 ` [PATCH 6/7] ath10k: Use new interfaces for MSI enablement Alexander Gordeev
2014-01-08 8:23 ` Kalle Valo
2014-01-08 9:04 ` Alexander Gordeev
2014-01-08 12:44 ` Kalle Valo
2014-01-07 18:05 ` [PATCH 7/7] wil6210: " Alexander Gordeev
2014-01-08 11:30 ` Vladimir Kondratiev
2014-01-08 11:54 ` Alexander Gordeev
2014-01-08 12:19 ` Vladimir Kondratiev
2014-01-08 12:34 ` Alexander Gordeev
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