MIPS: Ingenic: Disable broken BTB lookup optimization.

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

diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h
index 1e6966e..bdbdc19 100644 (file)
--- 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 634e94f..93b46be 100644 (file)
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -1946,6 +1946,13 @@ static inline void cpu_probe_ingenic(struct cpuinfo_mips *c, unsigned int cpu)
                c->cputype = CPU_XBURST;
                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!");