Introduce a new function pointer in the irq_chip structure(irq_set_auxdata)
which is responsible for updating data which is stored in a shared register
or data storage. For example, the idxd driver uses the auxiliary data API
to enable/set and disable PASID field that is in the IMS entry (introduced
in a later patch) and that data are not typically present in MSI entry.

Reviewed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Megha Dey <redacted>
---
 include/linux/interrupt.h |  2 ++
 include/linux/irq.h       |  4 ++++
 kernel/irq/manage.c       | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 967e257..461ed1c 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h

@@ -496,6 +496,8 @@ extern int irq_get_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
 extern int irq_set_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
 				 bool state);
 
+int irq_set_auxdata(unsigned int irq, unsigned int which, u64 val);
+
 #ifdef CONFIG_IRQ_FORCED_THREADING
 # ifdef CONFIG_PREEMPT_RT
 #  define force_irqthreads	(true)

diff --git a/include/linux/irq.h b/include/linux/irq.h
index 2efde6a..fc19f32 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h

@@ -491,6 +491,8 @@ static inline irq_hw_number_t irqd_to_hwirq(struct irq_data *d)
  *				irq_request_resources
  * @irq_compose_msi_msg:	optional to compose message content for MSI
  * @irq_write_msi_msg:	optional to write message content for MSI
+ * @irq_set_auxdata:	Optional function to update auxiliary data e.g. in
+ *			shared registers
  * @irq_get_irqchip_state:	return the internal state of an interrupt
  * @irq_set_irqchip_state:	set the internal state of a interrupt
  * @irq_set_vcpu_affinity:	optional to target a vCPU in a virtual machine

@@ -538,6 +540,8 @@ struct irq_chip {
 	void		(*irq_compose_msi_msg)(struct irq_data *data, struct msi_msg *msg);
 	void		(*irq_write_msi_msg)(struct irq_data *data, struct msi_msg *msg);
 
+	int		(*irq_set_auxdata)(struct irq_data *data, unsigned int which, u64 auxval);
+
 	int		(*irq_get_irqchip_state)(struct irq_data *data, enum irqchip_irq_state which, bool *state);
 	int		(*irq_set_irqchip_state)(struct irq_data *data, enum irqchip_irq_state which, bool state);
 

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 85ede4e..68ff559 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c

@@ -2860,3 +2860,35 @@ bool irq_check_status_bit(unsigned int irq, unsigned int bitmask)
 	return res;
 }
 EXPORT_SYMBOL_GPL(irq_check_status_bit);
+
+/**
+ * irq_set_auxdata - Set auxiliary data
+ * @irq:	Interrupt to update
+ * @which:	Selector which data to update
+ * @auxval:	Auxiliary data value
+ *
+ * Function to update auxiliary data for an interrupt, e.g. to update data
+ * which is stored in a shared register or data storage (e.g. IMS).
+ */
+int irq_set_auxdata(unsigned int irq, unsigned int which, u64 val)