Messages in this thread | | | Date | Tue, 4 Jul 2006 01:06:43 -0600 | From | Grant Grundler <> | Subject | Re: [patch 3/7] Check root chipset no_msi flag instead of all parent busses flags |
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On Sun, Jul 02, 2006 at 08:40:02PM -0400, Brice Goglin wrote: > MSI only requires support in the root chipset, which may not even have > a subordinate bus.
Brice, The above comment and the main part of this patch don't look right to me. Maybe it's the glass of wine I had two hours ago and it's around midnight now...
If the "root chipset" is not a PCI device and the architecture doesn't fake it, the root chipset (aka "PCI Host bus controller") is not visible to PCI subsystem. Some of the arch code (e.g. drivers/parisc/dino.c) uses "bus->self == NULL" to differentiate between PCI-PCI secondary busses and PCI bus below a "root chipset". ISTR alpha and sparc doing the same.
Can you confirm I'm remembering/understanding this bit correctly?
> pci_msi_supported() now checks the no_msi flag in the root_chipset pci_dev > struct instead of the PCI_BUS_FLAGS_NO_MSI flag of all its parent busses. > The MSI quirk now sets the no_msi flag accordingly.
I don't see how this could work for alpha/parisc/sparc (IIRC) or any other architecture that doesn't create "fake" PCI Root busses. I think your previous patch was correct in this regard.
> Index: linux-git/drivers/pci/msi.c > =================================================================== > --- linux-git.orig/drivers/pci/msi.c 2006-07-02 20:28:28.000000000 -0400 > +++ linux-git/drivers/pci/msi.c 2006-07-02 20:28:58.000000000 -0400 > @@ -905,19 +905,24 @@ > * @dev: pointer to the pci_dev data structure of MSI device function > * > * MSI must be globally enabled and supported by the device and > - * its parent busses. > + * its root chipset. > **/ > static > int pci_msi_supported(struct pci_dev * dev) > { > - struct pci_bus *bus; > + struct pci_dev *pdev; > > if (!pci_msi_enable || !dev || dev->no_msi) > return -1; > > - for (bus = dev->bus; bus; bus = bus->parent) > - if (bus->bus_flags & PCI_BUS_FLAGS_NO_MSI) > - return -1; > + /* find root complex for our device */ > + pdev = dev; > + while (pdev->bus && pdev->bus->self) > + pdev = pdev->bus->self;
In particular, I'm thinking this loop isn't correct though I'm not in a particular, erm, "certain" frame of mind right now. Under a parisc root device, pdev->bus->self would be NULL.
Maybe that's why parisc uses pci_scan_bus_parented() instead of pci_scan_bus(). (I've forgot the background behind that change).
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