linux-kernel - libata, devm

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Date:	Tue, 20 Jan 2009 11:03:13 -0500
From:	Mark Lord <liml@....ca>
To:	IDE/ATA development list <linux-ide@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Tejun Heo <htejun@...il.com>, Jeff Garzik <jgarzik@...ox.com>,
	linux-pci@...r.kernel.org
Subject: libata, devm_*, and MSI ?

Tejun / Jeff,

I am working on MSI support for sata_mv, and am trying to puzzle out
exactly what the kernel expects for this.  Looking at other drivers,
both libata and otherwise, yields a variety of conflicting implementations.

For starters, the MSI HOW-TO suggests that drivers must be careful
to invoke pci_disable_msi() on module unload, but I don't see that
happening anywhere in libata.

Unless, Tejun, the devm_* routines automatically do this.. do they?

Next, there's no mention of a need for invoking pci_intx() in the HOW-TO,
yet some device drivers call it, and others do not.

Eg. from ahci.c, we have this:

        if ((hpriv->flags & AHCI_HFLAG_NO_MSI) || pci_enable_msi(pdev))
                pci_intx(pdev, 1);

Which agrees with the existing code in sata_mv:

        if (msi && pci_enable_msi(pdev))
                pci_intx(pdev, 1);

Which seems to call pci_intx() only when MSI is *not* used.  Fine.
But then in sata_vsc.c, we do sort of the opposite:

        if (pci_enable_msi(pdev) == 0)
                pci_intx(pdev, 0);

Either that one is wrong, or pci_intx() is unnecessary in all cases.
Again, the MSI HOW-TO doesn't even mention this routine.

Looking through the network drivers, it seems that some of them
do the pci_intx(pdev,1) call for the cases where pci_enable_msi() fails,
similar to ahci.c and sata_mv.c.

But not all of them do that.

Perhaps somebody from the PCI side of things might enlighten us all.

Thanks

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