[tip: irq/msi] irqdomain: Add IRQ_DOMAIN_FLAG_MSI_IMMUTABLE and irq_domain_is_msi_immutable()

[tip-bot2 for Frank Li]

The following commit has been merged into the irq/msi branch of tip:

Commit-ID:     b8c7bfb7a0f01521297d688ca5fe1482c81e8910
Gitweb:        https://git.kernel.org/tip/b8c7bfb7a0f01521297d688ca5fe1482c81e8910
Author:        Frank Li <Frank.Li@xxxxxxx>
AuthorDate:    Mon, 14 Apr 2025 14:30:56 -04:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Wed, 07 May 2025 17:49:00 +02:00

irqdomain: Add IRQ_DOMAIN_FLAG_MSI_IMMUTABLE and irq_domain_is_msi_immutable()

Add the flag IRQ_DOMAIN_FLAG_MSI_IMMUTABLE and the API function
irq_domain_is_msi_immutable() to check if the MSI controller retains an
immutable address/data pair during irq_set_affinity().

Ensure compatibility with MSI users like PCIe Endpoint Doorbell, which
require the address/data pair to remain unchanged after setup. Use this
function to verify if the MSI controller is immutable.

Signed-off-by: Frank Li <Frank.Li@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/20250414-ep-msi-v18-2-f69b49917464@xxxxxxx

---
 include/linux/irqdomain.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/irqdomain.h b/include/linux/irqdomain.h
index bb71111..bccfff5 100644
--- a/include/linux/irqdomain.h
+++ b/include/linux/irqdomain.h
@@ -231,6 +231,9 @@ enum {
 	/* Irq domain must destroy generic chips when removed */
 	IRQ_DOMAIN_FLAG_DESTROY_GC	= (1 << 10),
 
+	/* Address and data pair is mutable when irq_set_affinity() */
+	IRQ_DOMAIN_FLAG_MSI_IMMUTABLE	= (1 << 11),
+
 	/*
 	 * Flags starting from IRQ_DOMAIN_FLAG_NONCORE are reserved
 	 * for implementation specific purposes and ignored by the
@@ -691,6 +694,10 @@ static inline bool irq_domain_is_msi_device(struct irq_domain *domain)
 	return domain->flags & IRQ_DOMAIN_FLAG_MSI_DEVICE;
 }
 
+static inline bool irq_domain_is_msi_immutable(struct irq_domain *domain)
+{
+	return domain->flags & IRQ_DOMAIN_FLAG_MSI_IMMUTABLE;
+}
 #else	/* CONFIG_IRQ_DOMAIN_HIERARCHY */
 static inline int irq_domain_alloc_irqs(struct irq_domain *domain,
 			unsigned int nr_irqs, int node, void *arg)