[PATCH 05/12] genirq/msi: Provide and use msi_domain_set_default_info_flags()

[Megha Dey <megha.dey@intel.com>]

From: Thomas Gleixner <tglx@linutronix.de>

MSI interrupts have some common flags which should be set not only for
PCI/MSI interrupts.

Move the PCI/MSI flag setting into a common function so it can be reused.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Megha Dey <megha.dey@intel.com>
---
 drivers/pci/msi.c   |  7 +------
 include/linux/msi.h |  1 +
 kernel/irq/msi.c    | 24 ++++++++++++++++++++++++
 3 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 3162f88..20d2512 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -1492,12 +1492,7 @@ 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;
-	if (IS_ENABLED(CONFIG_GENERIC_IRQ_RESERVATION_MODE))
-		info->flags |= MSI_FLAG_MUST_REACTIVATE;
-
-	/* PCI-MSI is oneshot-safe */
-	info->chip->flags |= IRQCHIP_ONESHOT_SAFE;
+	msi_domain_set_default_info_flags(info);
 
 	domain = msi_create_irq_domain(fwnode, info, parent);
 	if (!domain)
diff --git a/include/linux/msi.h b/include/linux/msi.h
index 89acc76..d7a7f7d 100644
--- a/include/linux/msi.h
+++ b/include/linux/msi.h
@@ -448,6 +448,7 @@ int platform_msi_domain_alloc(struct irq_domain *domain, unsigned int virq,
 void platform_msi_domain_free(struct irq_domain *domain, unsigned int virq,
 			      unsigned int nvec);
 void *platform_msi_get_host_data(struct irq_domain *domain);
+void msi_domain_set_default_info_flags(struct msi_domain_info *info);
 #endif /* CONFIG_GENERIC_MSI_IRQ_DOMAIN */
 
 #ifdef CONFIG_PCI_MSI_IRQ_DOMAIN
diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
index dc0e2d7..3697909 100644
--- a/kernel/irq/msi.c
+++ b/kernel/irq/msi.c
@@ -70,6 +70,30 @@ void get_cached_msi_msg(unsigned int irq, struct msi_msg *msg)
 EXPORT_SYMBOL_GPL(get_cached_msi_msg);
 
 #ifdef CONFIG_GENERIC_MSI_IRQ_DOMAIN
+void msi_domain_set_default_info_flags(struct msi_domain_info *info)
+{
+	/* Required so that a device latches a valid MSI message on startup */
+	info->flags |= MSI_FLAG_ACTIVATE_EARLY;
+
+	/*
+	 * Interrupt reservation mode allows to stear the MSI message of an
+	 * inactive device to a special (usually spurious interrupt) target.
+	 * This allows to prevent interrupt vector exhaustion e.g. on x86.
+	 * But (PCI)MSI interrupts are activated early - see above - so the
+	 * interrupt request/startup sequence would not try to allocate a
+	 * usable vector which means that the device interrupts would end
+	 * up on the special vector and issue spurious interrupt messages.
+	 * Setting the reactivation flag ensures that when the interrupt
+	 * is requested the activation is invoked again so that a real
+	 * vector can be allocated.
+	 */
+	if (IS_ENABLED(CONFIG_GENERIC_IRQ_RESERVATION_MODE))
+		info->flags |= MSI_FLAG_MUST_REACTIVATE;
+
+	/* MSI is oneshot-safe at least in theory */
+	info->chip->flags |= IRQCHIP_ONESHOT_SAFE;
+}
+
 static inline void irq_chip_write_msi_msg(struct irq_data *data,
 					  struct msi_msg *msg)
 {
-- 
2.7.4