[PATCH 3/4] irqchip, gicv3: Implement Cavium ThunderX erratum 23154

From: Robert Richter <redacted>

This patch implements Cavium ThunderX erratum 23154.

The gicv3 of ThunderX requires a modified version for reading the IAR
status to ensure data synchronization. Since this is in the fast-path
and called with each interrupt, runtime patching is used using jump
label patching for smallest overhead (no-op). This is the same
technique as used for tracepoints.

Signed-off-by: Robert Richter <redacted>
---
 drivers/irqchip/irq-gic-v3.c | 37 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index f4bafc69cc18..57bb69686ec6 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c

@@ -107,14 +107,38 @@ static void gic_redist_wait_for_rwp(void)
 }
 
 /* Low level accessors */
-static u64 __maybe_unused gic_read_iar(void)
+static u64 gic_read_iar_common(void)
+{
+	u64 irqstat;
+
+	asm volatile("mrs_s %0, " __stringify(ICC_IAR1_EL1) : "=r" (irqstat));
+	return irqstat;
+}
+
+/* Cavium ThunderX erratum 23154 */
+static u64 gic_read_iar_cavium_thunderx(void)
 {
 	u64 irqstat;
 
+	asm volatile("nop;nop;nop;nop;");
+	asm volatile("nop;nop;nop;nop;");
 	asm volatile("mrs_s %0, " __stringify(ICC_IAR1_EL1) : "=r" (irqstat));
+	asm volatile("nop;nop;nop;nop;");
+	mb();
+
 	return irqstat;
 }
 
+struct static_key is_cavium_thunderx = STATIC_KEY_INIT_FALSE;
+
+static u64 __maybe_unused gic_read_iar(void)
+{
+	if (static_key_false(&is_cavium_thunderx))
+		return gic_read_iar_common();
+	else
+		return gic_read_iar_cavium_thunderx();
+}
+
 static void __maybe_unused gic_write_pmr(u64 val)
 {
 	asm volatile("msr_s " __stringify(ICC_PMR_EL1) ", %0" : : "r" (val));

@@ -765,8 +789,19 @@ static const struct irq_domain_ops gic_irq_domain_ops = {
 	.free = gic_irq_domain_free,
 };
 
+static void gicv3_enable_cavium_thunderx(void *data)
+{
+	static_key_slow_inc(&is_cavium_thunderx);
+}
+
 static const struct gic_capabilities gicv3_errata[] = {
 	{
+		.desc	= "GIC: Cavium erratum 23154",
+		.id	= 0xa100034c,	/* ThunderX pass 1.x */
+		.mask	= 0xffff0fff,
+		.init	= gicv3_enable_cavium_thunderx,
+	},
+	{
 	}
 };