linux-kernel - Re: [PATCH] genirq/msi: Make sure PCI MSIs are activated early

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Date:	Tue, 26 Jul 2016 16:05:37 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Bjorn Helgaas <helgaas@...nel.org>
cc:	Marc Zyngier <marc.zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] genirq/msi: Make sure PCI MSIs are activated early

On Tue, 26 Jul 2016, Thomas Gleixner wrote:
> On Tue, 26 Jul 2016, Thomas Gleixner wrote:
> > On Mon, 25 Jul 2016, Bjorn Helgaas wrote:
> > > On Mon, Jul 25, 2016 at 09:45:13AM +0200, Thomas Gleixner wrote:
> > > I thought the original issue [1] was that PCI_MSI_FLAGS_ENABLE was being
> > > written before PCI_MSI_ADDRESS_LO.  That doesn't sound like a good
> > > idea to me.
> > 
> > Well. That's only a problem if the PCI device does not support masking. But
> > yes, we missed that case back then.
> >  
> > > That does seem like a problem.  Maybe it would be better to delay
> > > setting PCI_MSI_FLAGS_ENABLE until after the MSI address & data bits
> > > have been set?
> > 
> > I thought about that, but that gets ugly pretty fast. Here is an alternative
> > solution.
> > 
> > I think that's the proper place to do it _AFTER_ the hierarchical allocation
> > took place. On x86 Marc's ACTIVATE_EARLY flag would not work because the
> > message is not yet ready to be assembled.
> 
> Actually it works, because the MSI domain is the last one which is running the
> allocation function. So everything else is initialized already.
> 
> I'll take Marc's patch with some additional commentry as it turned out to be a
> workaround for the reported VMware issues with PCI/MSI-X pass through.

Now I digged a little bit deeper into all that PCI/MSI maze.

When a interrupt is freed, then we write the msi message to 0, but the
PCI_MSI_FLAGS_ENABLE flag is still set. That makes me wonder ...

Thanks,

	tglx