genirq: Introduce irq_chip.irq_compose_msi_msg() to support stacked irqchip

Add callback irq_compose_msi_msg to struct irq_chip, which will be used
to support stacked irqchip.

Signed-off-by: Jiang Liu <[e-mail]>
Cc: Bjorn Helgaas <[e-mail]>
Cc: Grant Likely <[e-mail]>
Cc: Marc Zyngier <[e-mail]>
Cc: Yingjoe Chen <[e-mail]>
Cc: Yijing Wang <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>

include/linux/irq.h

···
 struct module;
 struct irq_desc;
 struct irq_data;
+struct msi_msg;
 typedef	void (*irq_flow_handler_t)(unsigned int irq,
 					    struct irq_desc *desc);
 typedef	void (*irq_preflow_handler_t)(struct irq_data *data);
···
  *				any other callback related to this irq
  * @irq_release_resources:	optional to release resources acquired with
  *				irq_request_resources
+ * @irq_compose_msi_msg:	optional to compose message content for MSI
  * @flags:		chip specific flags
  */
 struct irq_chip {
···
 	void		(*irq_print_chip)(struct irq_data *data, struct seq_file *p);
 	int		(*irq_request_resources)(struct irq_data *data);
 	void		(*irq_release_resources)(struct irq_data *data);
+
+	void		(*irq_compose_msi_msg)(struct irq_data *data, struct msi_msg *msg);
 
 	unsigned long	flags;
 };
···
 extern void handle_bad_irq(unsigned int irq, struct irq_desc *desc);
 extern void handle_nested_irq(unsigned int irq);
 
+extern int irq_chip_compose_msi_msg(struct irq_data *data, struct msi_msg *msg);
 #ifdef	CONFIG_IRQ_DOMAIN_HIERARCHY
 extern void irq_chip_ack_parent(struct irq_data *data);
 extern int irq_chip_retrigger_hierarchy(struct irq_data *data);

kernel/irq/chip.c

···
 	return -ENOSYS;
 }
 #endif
+
+/**
+ * irq_chip_compose_msi_msg - Componse msi message for a irq chip
+ * @data:	Pointer to interrupt specific data
+ * @msg:	Pointer to the MSI message
+ *
+ * For hierarchical domains we find the first chip in the hierarchy
+ * which implements the irq_compose_msi_msg callback. For non
+ * hierarchical we use the top level chip.
+ */
+int irq_chip_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
+{
+	struct irq_data *pos = NULL;
+
+#ifdef	CONFIG_IRQ_DOMAIN_HIERARCHY
+	for (; data; data = data->parent_data)
+#endif
+		if (data->chip && data->chip->irq_compose_msi_msg)
+			pos = data;
+	if (!pos)
+		return -ENOSYS;
+
+	pos->chip->irq_compose_msi_msg(pos, msg);
+
+	return 0;
+}