[PATCH v2] irqchip/irq-brcmstb-l2: add write memory barrier before exit

[PATCH v2] irqchip/irq-brcmstb-l2: add write memory barrier before exit

[Florian Fainelli]

From: Doug Berger <opendmb@gmail.com>

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 irq could happen
before the brcmstb-l2 deasserted its output. This would lead the
GIC to reactivate the irq only to find that no L2 interrupt was
pending. The result was a spurious interrupt invoking the
handle_bad_irq() with its associated messaging. While this did
not create a functional problem it is a waste of cycles.

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. This commit adds 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 system.

Signed-off-by: Doug Berger <opendmb@gmail.com>
Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
Fixes: 7f646e92766e ("irqchip: brcmstb-l2: Add Broadcom Set Top Box  Level-2 interrupt controller")
[florian: Added Fixes tag]
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
---
Changes in v2:

- add Fixes tag
- bump copyright

 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 5559c943f03f..63aed60dd3f1 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);
 out:
+	/* Don't ack parent before all device writes are done */
+	wmb();
+
 	chained_irq_exit(chip, desc);
 }
 
-- 
2.34.1

[PATCH v2] irqchip/irq-brcmstb-l2: add write memory barrier before exit

[Florian Fainelli]

From: Doug Berger <opendmb@gmail.com>

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 irq could happen
before the brcmstb-l2 deasserted its output. This would lead the
GIC to reactivate the irq only to find that no L2 interrupt was
pending. The result was a spurious interrupt invoking the
handle_bad_irq() with its associated messaging. While this did
not create a functional problem it is a waste of cycles.

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. This commit adds 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 system.

Signed-off-by: Doug Berger <opendmb@gmail.com>
Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
Fixes: 7f646e92766e ("irqchip: brcmstb-l2: Add Broadcom Set Top Box  Level-2 interrupt controller")
[florian: Added Fixes tag]
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
---
Changes in v2:

- add Fixes tag
- bump copyright

 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 5559c943f03f..63aed60dd3f1 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);
 out:
+	/* Don't ack parent before all device writes are done */
+	wmb();
+
 	chained_irq_exit(chip, desc);
 }
 
-- 
2.34.1


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Re: [PATCH v2] irqchip/irq-brcmstb-l2: add write memory barrier before exit

[Marc Zyngier]

On Sat, 10 Feb 2024 01:24:49 +0000,
Florian Fainelli <florian.fainelli@broadcom.com> wrote:
> 
> From: Doug Berger <opendmb@gmail.com>
> 
> 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 irq could happen
> before the brcmstb-l2 deasserted its output. This would lead the
> GIC to reactivate the irq only to find that no L2 interrupt was
> pending. The result was a spurious interrupt invoking the
> handle_bad_irq() with its associated messaging. While this did
> not create a functional problem it is a waste of cycles.
> 
> 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. This commit adds 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 system.
> 
> Signed-off-by: Doug Berger <opendmb@gmail.com>
> Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
> Fixes: 7f646e92766e ("irqchip: brcmstb-l2: Add Broadcom Set Top Box  Level-2 interrupt controller")
> [florian: Added Fixes tag]
> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH v2] irqchip/irq-brcmstb-l2: add write memory barrier before exit

[Marc Zyngier]

On Sat, 10 Feb 2024 01:24:49 +0000,
Florian Fainelli <florian.fainelli@broadcom.com> wrote:
> 
> From: Doug Berger <opendmb@gmail.com>
> 
> 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 irq could happen
> before the brcmstb-l2 deasserted its output. This would lead the
> GIC to reactivate the irq only to find that no L2 interrupt was
> pending. The result was a spurious interrupt invoking the
> handle_bad_irq() with its associated messaging. While this did
> not create a functional problem it is a waste of cycles.
> 
> 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. This commit adds 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 system.
> 
> Signed-off-by: Doug Berger <opendmb@gmail.com>
> Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
> Fixes: 7f646e92766e ("irqchip: brcmstb-l2: Add Broadcom Set Top Box  Level-2 interrupt controller")
> [florian: Added Fixes tag]
> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.

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

[tip-bot2 for Doug Berger]

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@gmail.com>
AuthorDate:    Fri, 09 Feb 2024 17:24:49 -08:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
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
cycles.

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
system.

[ florian: Added Fixes tag ]

Fixes: 7f646e92766e ("irqchip: brcmstb-l2: Add Broadcom Set Top Box  Level-2 interrupt controller")
Signed-off-by: Doug Berger <opendmb@gmail.com>
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20240210012449.3009125-1-florian.fainelli@broadcom.com
---
 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);
 out:
+	/* Don't ack parent before all device writes are done */
+	wmb();
+
 	chained_irq_exit(chip, desc);
 }