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

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Date:	Wed, 13 Jul 2016 17:18:33 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>,
	<linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] genirq/msi: Make sure PCI MSIs are activated early

Bharat Kumar Gogada reported issues with the generic MSI code,
where the end-point ended up with garbage in its MSI configuration
(both for the vector and the message).

It turns out that the two MSI paths in the kernel are doing slightly
different things:

generic MSI: disable MSI -> allocate MSI -> enable MSI -> setup EP
PCI MSI: disable MSI -> allocate MSI -> setup EP -> enable MSI

and it turns out that end-points are allowed to latch the content
of the MSI configuration registers as soon as MSIs are enabled.
In Bharat's case, the end-point ends up using whatever was there
already, which is not what you want.

In order to make things converge, we introduce a new MSI domain
flag (MSI_FLAG_ACTIVATE_EARLY) that is unconditionally set for
PCI/MSI. When set, this flag forces the programming of the end-point
as soon as the MSIs are allocated.

A consequence of this is that we have an extra activate in
irq_startup, but that should be without much consequence.

Reported-by: Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
Tested-by: Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
Signed-off-by: Marc Zyngier <marc.zyngier@....com>
---
 drivers/pci/msi.c   | 2 ++
 include/linux/msi.h | 2 ++
 kernel/irq/msi.c    | 7 +++++++
 3 files changed, 11 insertions(+)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index a080f44..565e2a4 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -1277,6 +1277,8 @@ struct irq_domain *pci_msi_create_irq_domain(struct fwnode_handle *fwnode,
 	if (info->flags & MSI_FLAG_USE_DEF_CHIP_OPS)
 		pci_msi_domain_update_chip_ops(info);
 
+	info->flags |= MSI_FLAG_ACTIVATE_EARLY;
+
 	domain = msi_create_irq_domain(fwnode, info, parent);
 	if (!domain)
 		return NULL;
diff --git a/include/linux/msi.h b/include/linux/msi.h
index 8b425c6..513b7c7 100644
--- a/include/linux/msi.h
+++ b/include/linux/msi.h
@@ -270,6 +270,8 @@ enum {
 	MSI_FLAG_MULTI_PCI_MSI		= (1 << 3),
 	/* Support PCI MSIX interrupts */
 	MSI_FLAG_PCI_MSIX		= (1 << 4),
+	/* Needs early activate, required for PCI */
+	MSI_FLAG_ACTIVATE_EARLY		= (1 << 5),
 };
 
 int msi_domain_set_affinity(struct irq_data *data, const struct cpumask *mask,
diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
index 38e89ce..4ed2cca 100644
--- a/kernel/irq/msi.c
+++ b/kernel/irq/msi.c
@@ -361,6 +361,13 @@ int msi_domain_alloc_irqs(struct irq_domain *domain, struct device *dev,
 		else
 			dev_dbg(dev, "irq [%d-%d] for MSI\n",
 				virq, virq + desc->nvec_used - 1);
+
+		if (info->flags & MSI_FLAG_ACTIVATE_EARLY) {
+			struct irq_data *irq_data;
+
+			irq_data = irq_domain_get_irq_data(domain, desc->irq);
+			irq_domain_activate_irq(irq_data);
+		}
 	}
 
 	return 0;
-- 
2.1.4