On Tue, Jan 20, 2009 at 8:03 AM, Mark Lord <liml@xxxxxx> wrote: > 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. I don't think that's necessary if free_irq() or disable_irq() are called. However, I'm not seeing those get called either. > > 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. In general, I don't think drivers need to call pci_intx(). I'm really not sure why it's exported even. > > 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 && hi jiqi(pdev)) > pci_intx(pdev, 1); Combined with the fact that we can't find where MSI is disabled, this bit of code in pci_enable_msi() might cause MSI reload to fail: /* Check whether driver already requested for MSI-X irqs */ if (dev->msix_enabled) { dev_info(&dev->dev, "can't enable MSI " "(MSI-X already enabled)\n"); return -EINVAL; } > 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. Neither. Code in sata_vsc.c is redundant and can be removed. pci_intx() is necessary in some broken cases where INTX has to be _enabled_ for MSI to work: http://lkml.indiana.edu/hypermail/linux/kernel/0710.3/0772.html > 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. Jeff Garzik seems to like that construct: > > Perhaps somebody from the PCI side of things might enlighten us all. http://lists.linuxcoding.com/kernel/2005-q3/msg11296.html Shows when pci_intx() was added. linux-pci was NOT cc'd on that email. And no one asked for Documentation/ update. C'est la vie. BTW, gregkh is very good about posting patches when sending a pull request to linus. But that just means it was likely buried in a pile of 50+ patches. grant -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html