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

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Date:	Tue, 26 Jul 2016 13:42:21 +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 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.

Thanks,

	tglx
---
diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index a080f4496fe2..142341f8331b 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -645,6 +645,15 @@ static int msi_capability_init(struct pci_dev *dev, int nvec)
 		return ret;
 	}
 
+	/*
+	 * The mask can be ignored and PCI 2.3 does not specify mask bits for
+	 * each MSI interrupt. So in case of hierarchical irqdomains we need
+	 * to make sure that if masking is not available that the msi message
+	 * is written prior to setting the MSI enable bit in the device.
+	 */
+	if (pci_msi_ignore_mask || !entry->msi_attrib.maskbit)
+		irq_domain_activate_irq(irq_get_irq_data(entry->irq));
+
 	/* Set MSI enabled bits	 */
 	pci_intx_for_msi(dev, 0);
 	pci_msi_set_enable(dev, 1);