RE: [Penance PATCH] PCI: clean up the MSI code a bit

[Nguyen, Tom L]

On Thursday, June 09, 2005 4:49 PM Stefan Smietanowski wrote:
> pci_enable_msix(dev)
> {
>  if (is_dev_msi(dev))
>    pci_disable_msi(dev);
>  else if (is_dev_msix(dev))
>    return(ALREADY_MSIX);
>  else
>    return(MSIX_NOT_AVAILABLE);
>  if (!__pci_enable_msix(dev))
>    pci_enable_msi(dev);
>}
>
>That way noone needs to explicitly turn off msi as it's done
>automatically instead and the device will after this call
>always be in either MSIX, MSI or NORMAL IRQ mode, and
>always in the "best" mode the device, motherboard, bios, NB,
>whatever combination is available.

Your logic does not work because existing MSI/MSI-X code does not allow
a driver to switch back and forth between MSI mode and MSI-X mode. A
driver can switch interrupt mode between NORMAL IRQ mode and MSI mode or
between NORMAL IRQ mode and MSI-X mode but NOT between MSI mode and
MSI-X mode. A device driver should know well which MSI mode or MSI-X
mode it wants to run when its device supports both MSI and MSI-X
capability structures. Please read MSI-HOWTO before any attempt. If you
like to continue this path, then think of a better policy of how to
manage vector sources for MSI and MSI-X allocation before making
changes.

Thanks,
Long
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