irqchip/gic-v3: Workaround Marvell erratum 38545 when reading IAR

When a IAR register read races with a GIC interrupt RELEASE event,
GIC-CPU interface could wrongly return a valid INTID to the CPU
for an interrupt that is already released(non activated) instead of 0x3ff.

As a side effect, an interrupt handler could run twice, once with
interrupt priority and then with idle priority.

As a workaround, gic_read_iar is updated so that it will return a
valid interrupt ID only if there is a change in the active priority list
after the IAR read on all the affected Silicons.

Since there are silicon variants where both 23154 and 38545 are applicable,
workaround for erratum 23154 has been extended to address both of them.

Signed-off-by: Linu Cherian <lcherian@marvell.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220307143014.22758-1-lcherian@marvell.com
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 21 insertions, 2 deletions

diff --git a/arch/arm64/include/asm/arch_gicv3.h b/arch/arm64/include/asm/arch_gicv3.h
index 4ad22c3135db..8bd5afc7b692 100644
--- a/arch/arm64/include/asm/arch_gicv3.h
+++ b/arch/arm64/include/asm/arch_gicv3.h
@@ -53,17 +53,36 @@ static inline u64 gic_read_iar_common(void)
  * The gicv3 of ThunderX requires a modified version for reading the
  * IAR status to ensure data synchronization (access to icc_iar1_el1
  * is not sync'ed before and after).
+ *
+ * Erratum 38545
+ *
+ * When a IAR register read races with a GIC interrupt RELEASE event,
+ * GIC-CPU interface could wrongly return a valid INTID to the CPU
+ * for an interrupt that is already released(non activated) instead of 0x3ff.
+ *
+ * To workaround this, return a valid interrupt ID only if there is a change
+ * in the active priority list after the IAR read.
+ *
+ * Common function used for both the workarounds since,
+ * 1. On Thunderx 88xx 1.x both erratas are applicable.
+ * 2. Having extra nops doesn't add any side effects for Silicons where
+ *    erratum 23154 is not applicable.
  */
 static inline u64 gic_read_iar_cavium_thunderx(void)
 {
-	u64 irqstat;
+	u64 irqstat, apr;
 
+	apr = read_sysreg_s(SYS_ICC_AP1R0_EL1);
 	nops(8);
 	irqstat = read_sysreg_s(SYS_ICC_IAR1_EL1);
 	nops(4);
 	mb();
 
-	return irqstat;
+	/* Max priority groups implemented is only 32 */
+	if (likely(apr != read_sysreg_s(SYS_ICC_AP1R0_EL1)))
+		return irqstat;
+
+	return 0x3ff;
 }
 
 static inline void gic_write_ctlr(u32 val)