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Date: Tue, 8 Oct 2013 15:33:30 +1100 From: Michael Ellerman <michael@...erman.id.au> To: Alexander Gordeev <agordeev@...hat.com> Cc: linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>, Ralf Baechle <ralf@...ux-mips.org>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Martin Schwidefsky <schwidefsky@...ibm.com>, Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>, Dan Williams <dan.j.williams@...el.com>, Andy King <acking@...are.com>, Jon Mason <jon.mason@...el.com>, Matt Porter <mporter@...nel.crashing.org>, linux-pci@...r.kernel.org, linux-mips@...ux-mips.org, linuxppc-dev@...ts.ozlabs.org, linux390@...ibm.com, linux-s390@...r.kernel.org, x86@...nel.org, linux-ide@...r.kernel.org, iss_storagedev@...com, linux-nvme@...ts.infradead.org, linux-rdma@...r.kernel.org, netdev@...r.kernel.org, e1000-devel@...ts.sourceforge.net, linux-driver@...gic.com, Solarflare linux maintainers <linux-net-drivers@...arflare.com>, VMware@...p-26-207.brq.redhat.com, "Inc." <pv-drivers@...are.com>, linux-scsi@...r.kernel.org Subject: Re: [PATCH RFC 00/77] Re-design MSI/MSI-X interrupts enablement pattern 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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