irqchip/irq-msi-lib: Prepare for DEVICE MSI to replace platform MSI

Add the prerequisites for DEVICE MSI into the shared select() and child
domain init function. These domains are really trivial and just provide a
custom irq chip callback to write the MSI message.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Shivamurthy Shastri <shivamurthy.shastri@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240623142235.085171290@linutronix.de

drivers/irqchip/irq-msi-lib.c

@@ -56,6 +56,21 @@ bool msi_lib_init_dev_msi_info(struct device *dev, struct irq_domain *domain,
 		if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PCI_MSI)))
 			return false;
 
+		break;
+	case DOMAIN_BUS_DEVICE_MSI:
+		/*
+		 * Per device MSI should never have any MSI feature bits
+		 * set. It's sole purpose is to create a dumb interrupt
+		 * chip which has a device specific irq_write_msi_msg()
+		 * callback.
+		 */
+		if (WARN_ON_ONCE(info->flags))
+			return false;
+
+		/* Core managed MSI descriptors */
+		info->flags = MSI_FLAG_ALLOC_SIMPLE_MSI_DESCS | MSI_FLAG_FREE_MSI_DESCS;
+		/* Remove PCI specific flags */
+		required_flags &= ~MSI_FLAG_PCI_MSI_MASK_PARENT;
 		break;
 	default:
 		/*

drivers/irqchip/irq-msi-lib.h

@@ -15,6 +15,8 @@
 #define MATCH_PCI_MSI		(0)
 #endif
 
+#define MATCH_PLATFORM_MSI	BIT(DOMAIN_BUS_PLATFORM_MSI)
+
 int msi_lib_irq_domain_select(struct irq_domain *d, struct irq_fwspec *fwspec,
 			      enum irq_domain_bus_token bus_token);