linux-kernel - [PATCH v2] irqchip/irq-brcmstb-l2: Avoid saving mask on shutdown

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Date: Wed, 24 Apr 2024 10:57:32 -0700
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: linux-kernel@...r.kernel.org
Cc: Florian Fainelli <florian.fainelli@...adcom.com>,
	Tim Ross <tim.ross@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-mips@...r.kernel.org (open list:BROADCOM BMIPS MIPS ARCHITECTURE),
	linux-arm-kernel@...ts.infradead.org (moderated list:BROADCOM BCM7XXX ARM ARCHITECTURE)
Subject: [PATCH v2] irqchip/irq-brcmstb-l2: Avoid saving mask on shutdown

The interrupt controller shutdown path does not need to save the mask of
enabled interrupts because the next state the system is going to be in
is akin to a cold boot, or a kexec'd kernel. Saving the mask only makes
sense if the software state needs to preserve the hardware state across
a system suspend/resume cycle.

As an optimization, and given that there are systems with dozens of such
interrupt controller, we can save a "slow" memory mapped I/O read in the
shutdown path where no saving/restoring is required.

Reported-by: Tim Ross <tim.ross@...adcom.com>
Signed-off-by: Florian Fainelli <florian.fainelli@...adcom.com>
---

Changes in v2:

- expand the commit message to explain this is an optimiation saving a
  slow MMIO read

 drivers/irqchip/irq-brcmstb-l2.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/irqchip/irq-brcmstb-l2.c b/drivers/irqchip/irq-brcmstb-l2.c
index 2b0b3175cea0..c988886917f7 100644
--- a/drivers/irqchip/irq-brcmstb-l2.c
+++ b/drivers/irqchip/irq-brcmstb-l2.c
@@ -118,7 +118,7 @@ static void brcmstb_l2_intc_irq_handle(struct irq_desc *desc)
 	chained_irq_exit(chip, desc);
 }
 
-static void brcmstb_l2_intc_suspend(struct irq_data *d)
+static void __brcmstb_l2_intc_suspend(struct irq_data *d, bool save)
 {
 	struct irq_chip_generic *gc = irq_data_get_irq_chip_data(d);
 	struct irq_chip_type *ct = irq_data_get_chip_type(d);
@@ -127,7 +127,8 @@ static void brcmstb_l2_intc_suspend(struct irq_data *d)
 
 	irq_gc_lock_irqsave(gc, flags);
 	/* Save the current mask */
-	b->saved_mask = irq_reg_readl(gc, ct->regs.mask);
+	if (save)
+		b->saved_mask = irq_reg_readl(gc, ct->regs.mask);
 
 	if (b->can_wake) {
 		/* Program the wakeup mask */
@@ -137,6 +138,16 @@ static void brcmstb_l2_intc_suspend(struct irq_data *d)
 	irq_gc_unlock_irqrestore(gc, flags);
 }
 
+static void brcmstb_l2_intc_shutdown(struct irq_data *d)
+{
+	__brcmstb_l2_intc_suspend(d, false);
+}
+
+static void brcmstb_l2_intc_suspend(struct irq_data *d)
+{
+	__brcmstb_l2_intc_suspend(d, true);
+}
+
 static void brcmstb_l2_intc_resume(struct irq_data *d)
 {
 	struct irq_chip_generic *gc = irq_data_get_irq_chip_data(d);
@@ -252,7 +263,7 @@ static int __init brcmstb_l2_intc_of_init(struct device_node *np,
 
 	ct->chip.irq_suspend = brcmstb_l2_intc_suspend;
 	ct->chip.irq_resume = brcmstb_l2_intc_resume;
-	ct->chip.irq_pm_shutdown = brcmstb_l2_intc_suspend;
+	ct->chip.irq_pm_shutdown = brcmstb_l2_intc_shutdown;
 
 	if (data->can_wake) {
 		/* This IRQ chip can wake the system, set all child interrupts
-- 
2.34.1