Re: [RFC PATCH] PCI: remove access to pci_[enable|disable]_msi() for drivers

[Stefan Smietanowski <stesmi@stesmi.com>]

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Hi Greg.

>>>>* What if the driver writer does not want MSI enabled for their
>>>>  hardware (even though there is an MSI capabilities entry)?  Reasons
>>>>  include: overhead involved in initiating the MSI; no support in some
>>>>  versions of firmware (QLogic hardware).
>>>
>>>Yes, a very good point.  I guess I should keep the pci_enable_msi() and
>>>pci_disable_msi() functions exported for this reason.
>>>
>>
>>well... only pci_disable_msi() is needed for this ;)
> 
> I thought so too, until I looked at the IB driver :(
> 
> The issue is, if pci_enable_msix() fails, we want to fall back to MSI,
> so you need to call pci_enable_msi() for that (after calling
> pci_disable_msi() before calling pci_enable_msix(), what a mess...)
> 
> So we still need both functions, and for MSI-X, the logic involved in
> enabling it is horrible.  Let me see if this can be made saner...

Why not make pci_switch_to_msix() (yeah, horrible name) instead?

pci_switch_to_msix(dev)
{
  pci_disable_msi(dev);
  if (!psi_enable_msix(dev))
    pci_enable_msi(dev);
}

And it can naturally inform the caller if it failed or not.

// Stefan
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