[PATCH 1/3] MIPS: Introduce WAR_4KC_LLSC config option

[Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>]

WAR_4KC_LLSC is used to control workaround of 4KC LLSC issue
that affects 4Kc up to version 0.9.

Early ath25 chips are known to be affected.

Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
---
 arch/mips/Kconfig                                        | 6 ++++++
 arch/mips/include/asm/cpu.h                              | 1 +
 arch/mips/include/asm/mach-ath25/cpu-feature-overrides.h | 2 +-
 arch/mips/kernel/cpu-probe.c                             | 7 +++++++
 4 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 30e90a2d53f4..354d033364ad 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -230,6 +230,7 @@ config ATH25
 	select SYS_SUPPORTS_BIG_ENDIAN
 	select SYS_SUPPORTS_32BIT_KERNEL
 	select SYS_HAS_EARLY_PRINTK
+	select WAR_4KC_LLSC if !SOC_AR5312
 	help
 	  Support for Atheros AR231x and Atheros AR531x based boards
 
@@ -2544,6 +2545,11 @@ config WAR_ICACHE_REFILLS
 config WAR_R10000_LLSC
 	bool
 
+# On 4Kc up to version 0.9 (PRID_REV < 1) there is a bug that may cause llsc
+# sequences to deadlock.
+config WAR_4KC_LLSC
+	bool
+
 # 34K core erratum: "Problems Executing the TLBR Instruction"
 config WAR_MIPS34K_MISSED_ITLB
 	bool
diff --git a/arch/mips/include/asm/cpu.h b/arch/mips/include/asm/cpu.h
index ecb9854cb432..84bb1931a8b4 100644
--- a/arch/mips/include/asm/cpu.h
+++ b/arch/mips/include/asm/cpu.h
@@ -247,6 +247,7 @@
 #define PRID_REV_VR4122			0x0070
 #define PRID_REV_VR4181A		0x0070	/* Same as VR4122 */
 #define PRID_REV_VR4130			0x0080
+#define PRID_REV_4KC_V1_0		0x0001
 #define PRID_REV_34K_V1_0_2		0x0022
 #define PRID_REV_LOONGSON1B		0x0020
 #define PRID_REV_LOONGSON1C		0x0020	/* Same as Loongson-1B */
diff --git a/arch/mips/include/asm/mach-ath25/cpu-feature-overrides.h b/arch/mips/include/asm/mach-ath25/cpu-feature-overrides.h
index ec3604c44ef2..5df292b1ff04 100644
--- a/arch/mips/include/asm/mach-ath25/cpu-feature-overrides.h
+++ b/arch/mips/include/asm/mach-ath25/cpu-feature-overrides.h
@@ -24,7 +24,7 @@
 #define cpu_has_counter			1
 #define cpu_has_ejtag			1
 
-#if !defined(CONFIG_SOC_AR5312)
+#if !defined(WAR_4KC_LLSC)
 #  define cpu_has_llsc			1
 #else
 /*
diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c
index 6d15a398d389..fd452e68cd90 100644
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -152,6 +152,13 @@ static inline void check_errata(void)
 	struct cpuinfo_mips *c = &current_cpu_data;
 
 	switch (current_cpu_type()) {
+	case CPU_4KC:
+		if ((c->processor_id & PRID_REV_MASK) < PRID_REV_4KC_V1_0) {
+			c->options &= ~MIPS_CPU_LLSC;
+			if (!IS_ENABLED(CONFIG_WAR_4K_LLSC))
+				pr_err("CPU have LLSC errata, please enable CONFIG_WAR_4K_LLSC");
+		}
+		break;
 	case CPU_34K:
 		/*
 		 * Erratum "RPS May Cause Incorrect Instruction Execution"
-- 
2.39.2 (Apple Git-143)