[PATCH v2 4/8] irqchip/al-fic: switch to shared parent interrupt

[Eliav Farber]

Until now the driver requested its parent interrupt using the chained IRQ
API (irq_set_chained_handler_and_data()), which only works when each
parent interrupt is wired to a single FIC instance.

A FIC controller is built from groups, each described by its own DT node,
and the groups of one controller share that controller's output line
toward the parent. So a real devicetree has several FIC nodes on one
parent GIC SPI, and a chained handler can only be installed once per
parent. Cascading compounds this: an aggregating group collects several
peripherals' outputs onto the line above it.

To support that, request the parent interrupt as a shared interrupt
(IRQF_SHARED) instead of installing a chained handler. The handler now has
the standard irqreturn_t prototype and reports whether it handled any
child interrupt, so the shared-IRQ core can dispatch to the correct
instance. IRQF_NO_THREAD is set because the handler only demultiplexes to
the child domain and must not be forced-threaded; all instances sharing a
parent line agree on this flag, as the shared-IRQ core requires.

generic_handle_domain_irq() is retained for dispatch; its return value is
used to determine whether a pending child was actually handled so the
handler can return IRQ_HANDLED/IRQ_NONE correctly.

request_irq() can fail, unlike irq_set_chained_handler_and_data(), so add
an error path for it. It calls irq_domain_remove_generic_chips() before
irq_domain_remove(), because irq_domain_remove() frees the generic chips
only when the domain carries IRQ_DOMAIN_FLAG_DESTROY_GC.

Co-developed-by: Talel Shenhar <talel@xxxxxxxxxx>
Signed-off-by: Talel Shenhar <talel@xxxxxxxxxx>
Signed-off-by: Eliav Farber <farbere@xxxxxxxxxx>
---
v2:
 - Fix the request_irq() error path: v1 called irq_free_generic_chip(gc),
   which is kfree(gc) on an interior pointer into the single allocation
   made by irq_domain_alloc_generic_chips() - an invalid free reachable
   when request_irq() fails at probe. Replace it with
   irq_domain_remove_generic_chips() before irq_domain_remove(), and add a
   commit-message paragraph explaining the teardown ordering.
 - Add Co-developed-by/Signed-off-by: Talel Shenhar.
 - Reworded to state the hardware reason for the shared parent (the groups
   of one controller share that controller's output line).

 drivers/irqchip/irq-al-fic.c | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/drivers/irqchip/irq-al-fic.c b/drivers/irqchip/irq-al-fic.c
index c7cc2631caf8..091a06abc0bb 100644
--- a/drivers/irqchip/irq-al-fic.c
+++ b/drivers/irqchip/irq-al-fic.c
@@ -4,9 +4,9 @@
  */
 
 #include <linux/bitfield.h>
+#include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/irqchip.h>
-#include <linux/irqchip/chained_irq.h>
 #include <linux/irqdomain.h>
 #include <linux/module.h>
 #include <linux/of.h>
@@ -95,24 +95,24 @@ static int al_fic_irq_set_type(struct irq_data *data, unsigned int flow_type)
 	return 0;
 }
 
-static void al_fic_irq_handler(struct irq_desc *desc)
+static irqreturn_t al_fic_irq_handler(int irq, void *data)
 {
-	struct al_fic *fic = irq_desc_get_handler_data(desc);
+	struct al_fic *fic = data;
 	struct irq_domain *domain = fic->domain;
-	struct irq_chip *irqchip = irq_desc_get_chip(desc);
 	struct irq_chip_generic *gc = irq_get_domain_generic_chip(domain, 0);
+	irqreturn_t ret = IRQ_NONE;
 	unsigned long pending;
 	u32 hwirq;
 
-	chained_irq_enter(irqchip, desc);
-
 	pending = readl_relaxed(fic->base + AL_FIC_CAUSE);
 	pending &= ~gc->mask_cache;
 
-	for_each_set_bit(hwirq, &pending, NR_FIC_IRQS)
-		generic_handle_domain_irq(domain, hwirq);
+	for_each_set_bit(hwirq, &pending, NR_FIC_IRQS) {
+		if (!generic_handle_domain_irq(domain, hwirq))
+			ret = IRQ_HANDLED;
+	}
 
-	chained_irq_exit(irqchip, desc);
+	return ret;
 }
 
 static int al_fic_irq_retrigger(struct irq_data *data)
@@ -162,11 +162,18 @@ static int al_fic_register(struct device_node *node,
 	gc->chip_types->chip.flags = IRQCHIP_SKIP_SET_WAKE;
 	gc->private = fic;
 
-	irq_set_chained_handler_and_data(fic->parent_irq,
-					 al_fic_irq_handler,
-					 fic);
+	ret = request_irq(fic->parent_irq, al_fic_irq_handler,
+			  IRQF_NO_THREAD | IRQF_SHARED, fic->node->full_name,
+			  fic);
+	if (ret) {
+		pr_err("fail to request irq (%d)\n", ret);
+		goto err_remove_generic_chips;
+	}
+
 	return 0;
 
+err_remove_generic_chips:
+	irq_domain_remove_generic_chips(fic->domain);
 err_domain_remove:
 	irq_domain_remove(fic->domain);
 
-- 
2.47.3