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Subject[PATCH 5.2 090/137] MIPS: Ingenic: Disable broken BTB lookup optimization.
Date
From: Zhou Yanjie <zhouyanjie@zoho.com>

[ Upstream commit 053951dda71ecb4b554a2cdbe26f5f6f9bee9dd2 ]

In order to further reduce power consumption, the XBurst core
by default attempts to avoid branch target buffer lookups by
detecting & special casing loops. This feature will cause
BogoMIPS and lpj calculate in error. Set cp0 config7 bit 4 to
disable this feature.

Signed-off-by: Zhou Yanjie <zhouyanjie@zoho.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: ralf@linux-mips.org
Cc: paul@crapouillou.net
Cc: jhogan@kernel.org
Cc: malat@debian.org
Cc: gregkh@linuxfoundation.org
Cc: tglx@linutronix.de
Cc: allison@lohutok.net
Cc: syq@debian.org
Cc: chenhc@lemote.com
Cc: jiaxun.yang@flygoat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/mips/include/asm/mipsregs.h | 4 ++++
arch/mips/kernel/cpu-probe.c | 7 +++++++
2 files changed, 11 insertions(+)

diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h
index 1e6966e8527e9..bdbdc19a2b8f8 100644
--- a/arch/mips/include/asm/mipsregs.h
+++ b/arch/mips/include/asm/mipsregs.h
@@ -689,6 +689,9 @@
#define MIPS_CONF7_IAR (_ULCAST_(1) << 10)
#define MIPS_CONF7_AR (_ULCAST_(1) << 16)

+/* Ingenic Config7 bits */
+#define MIPS_CONF7_BTB_LOOP_EN (_ULCAST_(1) << 4)
+
/* Config7 Bits specific to MIPS Technologies. */

/* Performance counters implemented Per TC */
@@ -2813,6 +2816,7 @@ __BUILD_SET_C0(status)
__BUILD_SET_C0(cause)
__BUILD_SET_C0(config)
__BUILD_SET_C0(config5)
+__BUILD_SET_C0(config7)
__BUILD_SET_C0(intcontrol)
__BUILD_SET_C0(intctl)
__BUILD_SET_C0(srsmap)
diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c
index 9635c1db3ae6a..e654ffc1c8a0d 100644
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -1964,6 +1964,13 @@ static inline void cpu_probe_ingenic(struct cpuinfo_mips *c, unsigned int cpu)
c->cputype = CPU_JZRISC;
c->writecombine = _CACHE_UNCACHED_ACCELERATED;
__cpu_name[cpu] = "Ingenic JZRISC";
+ /*
+ * The XBurst core by default attempts to avoid branch target
+ * buffer lookups by detecting & special casing loops. This
+ * feature will cause BogoMIPS and lpj calculate in error.
+ * Set cp0 config7 bit 4 to disable this feature.
+ */
+ set_c0_config7(MIPS_CONF7_BTB_LOOP_EN);
break;
default:
panic("Unknown Ingenic Processor ID!");
--
2.20.1


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