Re: [Xen-devel] [PATCH v5 5/6] xen/x86: add PHYSDEVOP_msi_control

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Jul 18, 2019 at 03:17:27PM +0000, Jan Beulich wrote:
> On 18.07.2019 15:46, Roger Pau Monné  wrote:
> > In fact I don't think INTx should be enabled when MSI(-X) is disabled,
> > QEMU already traps writes to the command register, and it will manage
> > INTx enabling/disabling by itself. I think the only check required is
> > that MSI(-X) cannot be enabled if INTx is also enabled. In the same
> > way both MSI caspabilities cannot be enabled simultaneously. The
> > function should not explicitly disable any of the other capabilities,
> > and just return -EBUSY if the caller attempts for example to enable
> > MSI while INTx or MSI-X is enabled.
> 
> You do realize that pci_intx() only ever gets called for Xen
> internally used interrupts, i.e. mainly the serial console one?

You will have to bear with me because I'm not sure I understand why
it does matter. Do you mean to point out that dom0 is the one in full
control of INTx, and thus Xen shouldn't care of whether INTx and
MSI(-X) are enabled at the same time?

I still think that at least a warning should be printed if a caller
tries to enable MSI(-X) while INTx is also enabled, but unless there's
a reason to have both MSI(-X) and INTx enabled at the same time (maybe
a quirk for some hardware issue?) it shouldn't be allowed on this new
interface.

Thanks, Roger.

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