genirq: Generic chip: add irq_unmap_generic_chip

Without this patch irq_domain_disassociate() cannot properly release the interrupt.
Indeed, irq_map_generic_chip() checks a bit on 'gc->installed' but said bit is never cleared, only set.

Commit 088f40b7b027 ("genirq: Generic chip: Add linear irq domain support") added irq_map_generic_chip() function and also stated "This lacks a removal function for now".

This commit provides with an implementation of an unmap function that can be called by irq_domain_disassociate().

Fixes 088f40b7b027 ("genirq: Generic chip: Add linear irq domain support")

Signed-off-by Sebastian Frias <[email protected]>

---

This is required by loadable modules requesting IRQs.
In our case rmmod will perform free_irq() + irq_dispose_mapping(). Without the unmap call the module cannot request the IRQ after "rmmod" because it is marked as "installed" by the first successful "insmod".

NOTE: While the proposed unmap() function attempts to undo as much things as done by the map() function, I did not find a way to undo the following:

a) irq_gc_init_mask_cache(gc, dgc->gc_flags)
b) irq_set_lockdep_class(virq, &irq_nested_lock_class)
c) irq_modify_status(virq, dgc->irq_flags_to_clear, dgc->irq_flags_to_set)

Feel free to comment on that matter.

---
 kernel/irq/generic-chip.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

kernel/irq/generic-chip.c +26 -0

index abd286a..7b464cd 100644
@@ -411,8 +411,34 @@ int irq_map_generic_chip(struct irq_domain *d, unsigned int virq,
 }
 EXPORT_SYMBOL_GPL(irq_map_generic_chip);
 
+void irq_unmap_generic_chip(struct irq_domain *d, unsigned int virq)
+{
+	struct irq_data *data = irq_domain_get_irq_data(d, virq);
+	struct irq_domain_chip_generic *dgc = d->gc;
+	struct irq_chip_generic *gc;
+	unsigned int hw_irq = data->hwirq;
+	int chip_idx, irq_idx;
+
+	if (!d->gc)
+		return;
+
+	chip_idx = hw_irq / dgc->irqs_per_chip;
+	if (chip_idx >= dgc->num_chips)
+		return;
+	gc = dgc->gc[chip_idx];
+
+	irq_idx = hw_irq % dgc->irqs_per_chip;
+
+	clear_bit(irq_idx, &gc->installed);
+	irq_domain_set_info(d, virq, hw_irq,
+			    &no_irq_chip, NULL, NULL, NULL, NULL);
+
+}
+EXPORT_SYMBOL_GPL(irq_unmap_generic_chip);
+
 struct irq_domain_ops irq_generic_chip_ops = {
 	.map	= irq_map_generic_chip,
+	.unmap  = irq_unmap_generic_chip,
 	.xlate	= irq_domain_xlate_onetwocell,
 };
 EXPORT_SYMBOL_GPL(irq_generic_chip_ops);

NOTE: While the proposed unmap() function attempts to undo as much things as done by the map() function, I did not find a way to undo the following:

a) irq_gc_init_mask_cache(gc, dgc->gc_flags)

b) irq_set_lockdep_class(virq, &irq_nested_lock_class)

c) irq_modify_status(virq, dgc->irq_flags_to_clear, dgc->irq_flags_to_set)

Quoted 4 lines · Sebastian Frias

NOTE: While the proposed unmap() function attempts to undo as much things as done by the map() function, I did not find a way to undo the following:

a) irq_gc_init_mask_cache(gc, dgc->gc_flags)

You can't undo that. Because that represents the mask cache of the irq chip and that is required to be consistent over the life time of the irq chip.

Unmapping does not make the generic chip and the underlying irqchip go away.

Quoted 1 line

b) irq_set_lockdep_class(virq, &irq_nested_lock_class)

No point in undoing that. The irq descriptor is released on unmap.

Quoted 1 line

c) irq_modify_status(virq, dgc->irq_flags_to_clear, dgc->irq_flags_to_set)

See b)