[tip: irq/urgent] irqchip/irq-brcmstb-l2: Add write memory barrier before exit

From: tip-bot2 for Doug Berger
Date: Tue Feb 13 2024 - 03:40:12 EST

The following commit has been merged into the irq/urgent branch of tip:

Commit-ID: b0344d6854d25a8b3b901c778b1728885dd99007
Gitweb: https://git.kernel.org/tip/b0344d6854d25a8b3b901c778b1728885dd99007
Author: Doug Berger <opendmb@xxxxxxxxx>
AuthorDate: Fri, 09 Feb 2024 17:24:49 -08:00
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Tue, 13 Feb 2024 09:33:31 +01:00

irqchip/irq-brcmstb-l2: Add write memory barrier before exit

It was observed on Broadcom devices that use GIC v3 architecture L1
interrupt controllers as the parent of brcmstb-l2 interrupt controllers
that the deactivation of the parent interrupt could happen before the
brcmstb-l2 deasserted its output. This would lead the GIC to reactivate the
interrupt only to find that no L2 interrupt was pending. The result was a
spurious interrupt invoking handle_bad_irq() with its associated
messaging. While this did not create a functional problem it is a waste of

The hazard exists because the memory mapped bus writes to the brcmstb-l2
registers are buffered and the GIC v3 architecture uses a very efficient
system register write to deactivate the interrupt.

Add a write memory barrier prior to invoking chained_irq_exit() to
introduce a dsb(st) on those systems to ensure the system register write
cannot be executed until the memory mapped writes are visible to the

[ florian: Added Fixes tag ]

Fixes: 7f646e92766e ("irqchip: brcmstb-l2: Add Broadcom Set Top Box Level-2 interrupt controller")
Signed-off-by: Doug Berger <opendmb@xxxxxxxxx>
Signed-off-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
Acked-by: Marc Zyngier <maz@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20240210012449.3009125-1-florian.fainelli@xxxxxxxxxxxx
drivers/irqchip/irq-brcmstb-l2.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/irqchip/irq-brcmstb-l2.c b/drivers/irqchip/irq-brcmstb-l2.c
index 5559c94..2b0b317 100644
--- a/drivers/irqchip/irq-brcmstb-l2.c
+++ b/drivers/irqchip/irq-brcmstb-l2.c
@@ -2,7 +2,7 @@
* Generic Broadcom Set Top Box Level 2 Interrupt controller driver
- * Copyright (C) 2014-2017 Broadcom
+ * Copyright (C) 2014-2024 Broadcom

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
@@ -112,6 +112,9 @@ static void brcmstb_l2_intc_irq_handle(struct irq_desc *desc)
generic_handle_domain_irq(b->domain, irq);
} while (status);
+ /* Don't ack parent before all device writes are done */
+ wmb();
chained_irq_exit(chip, desc);