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Subject[patch V2 43/46] genirq/msi: Provide and use msi_domain_set_default_info_flags()
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>
---
V2: New patch
---
drivers/pci/msi.c | 7 +------
include/linux/msi.h | 1 +
kernel/irq/msi.c | 24 ++++++++++++++++++++++++
3 files changed, 26 insertions(+), 6 deletions(-)

--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -1469,12 +1469,7 @@ struct irq_domain *pci_msi_create_irq_do
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)
--- a/include/linux/msi.h
+++ b/include/linux/msi.h
@@ -410,6 +410,7 @@ int platform_msi_domain_alloc(struct irq
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
--- a/kernel/irq/msi.c
+++ b/kernel/irq/msi.c
@@ -70,6 +70,30 @@ void get_cached_msi_msg(unsigned int irq
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 interupts 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)
{
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