MIPS: Ingenic: Disable broken BTB lookup optimization.

[ Upstream commit 053951dd ]

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

@@ -688,6 +688,9 @@
 #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 */
@@ -2774,6 +2777,7 @@ __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)

arch/mips/kernel/cpu-probe.c

@@ -1879,6 +1879,13 @@ 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!");