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MIPS: Ingenic: Disable broken BTB lookup optimization.

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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
This commit is contained in:
Zhou Yanjie 2019-08-02 16:27:37 +08:00 committed by Paul Burton
parent 579de8f86b
commit 053951dda7
No known key found for this signature in database
GPG key ID: 3EA79FACB57500DD
2 changed files with 11 additions and 0 deletions
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4
arch/mips/include/asm/mipsregs.h
View file

@ -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)

7
arch/mips/kernel/cpu-probe.c
View file

@ -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!");