[PATCH 4/5] irqchip/sifive-plic: Make better use of the effective affinity mask

[Samuel Holland <samuel@sholland.org>]

The PLIC driver already updates the effective affinity mask in its
.irq_set_affinity callback. Take advantage of that information to only
touch bits (and take spinlocks) for the specific relevant hart contexts.

First, make sure the effective affinity mask is set before IRQ startup.
Since this mask already takes priv->lmask into account, checking that
mask later is no longer needed (and handler->present is equivalent to
the bit being set in priv->lmask).

Then, when (un)masking or changing affinity, only clear/set the enable
bits in the specific old/new context(s). The cpumask operations in
plic_irq_unmask() are not needed because they duplicate the code in
plic_set_affinity().

Signed-off-by: Samuel Holland <samuel@sholland.org>
---

 drivers/irqchip/Kconfig           |  1 +
 drivers/irqchip/irq-sifive-plic.c | 26 ++++++++------------------
 2 files changed, 9 insertions(+), 18 deletions(-)

diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
index bc90500a7573..56ef2fc6d2eb 100644
--- a/drivers/irqchip/Kconfig
+++ b/drivers/irqchip/Kconfig
@@ -529,6 +529,7 @@ config SIFIVE_PLIC
 	bool "SiFive Platform-Level Interrupt Controller"
 	depends on RISCV
 	select IRQ_DOMAIN_HIERARCHY
+	select GENERIC_IRQ_EFFECTIVE_AFF_MASK if SMP
 	help
 	   This enables support for the PLIC chip found in SiFive (and
 	   potentially other) RISC-V systems.  The PLIC controls devices
diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
index bb87e4c3b88e..bf7d5bee0c0c 100644
--- a/drivers/irqchip/irq-sifive-plic.c
+++ b/drivers/irqchip/irq-sifive-plic.c
@@ -109,31 +109,18 @@ static inline void plic_irq_toggle(const struct cpumask *mask,
 	for_each_cpu(cpu, mask) {
 		struct plic_handler *handler = per_cpu_ptr(&plic_handlers, cpu);
 
-		if (handler->present &&
-		    cpumask_test_cpu(cpu, &handler->priv->lmask))
-			plic_toggle(handler, d->hwirq, enable);
+		plic_toggle(handler, d->hwirq, enable);
 	}
 }
 
 static void plic_irq_unmask(struct irq_data *d)
 {
-	struct cpumask amask;
-	unsigned int cpu;
-	struct plic_priv *priv = irq_data_get_irq_chip_data(d);
-
-	cpumask_and(&amask, &priv->lmask, cpu_online_mask);
-	cpu = cpumask_any_and(irq_data_get_affinity_mask(d),
-					   &amask);
-	if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
-		return;
-	plic_irq_toggle(cpumask_of(cpu), d, 1);
+	plic_irq_toggle(irq_data_get_effective_affinity_mask(d), d, 1);
 }
 
 static void plic_irq_mask(struct irq_data *d)
 {
-	struct plic_priv *priv = irq_data_get_irq_chip_data(d);
-
-	plic_irq_toggle(&priv->lmask, d, 0);
+	plic_irq_toggle(irq_data_get_effective_affinity_mask(d), d, 0);
 }
 
 #ifdef CONFIG_SMP
@@ -154,11 +141,13 @@ static int plic_set_affinity(struct irq_data *d,
 	if (cpu >= nr_cpu_ids)
 		return -EINVAL;
 
-	plic_irq_toggle(&priv->lmask, d, 0);
-	plic_irq_toggle(cpumask_of(cpu), d, !irqd_irq_masked(d));
+	plic_irq_mask(d);
 
 	irq_data_update_effective_affinity(d, cpumask_of(cpu));
 
+	if (!irqd_irq_masked(d))
+		plic_irq_unmask(d);
+
 	return IRQ_SET_MASK_OK_DONE;
 }
 #endif
@@ -184,6 +173,7 @@ static struct irq_chip plic_chip = {
 #ifdef CONFIG_SMP
 	.irq_set_affinity = plic_set_affinity,
 #endif
+	.flags		= IRQCHIP_AFFINITY_PRE_STARTUP,
 };
 
 static int plic_irqdomain_map(struct irq_domain *d, unsigned int irq,
-- 
2.35.1