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| author | WANG Xuerui <git@xen0n.name> | 2020-05-23 21:37:01 +0800 |
|---|---|---|
| committer | Thomas Bogendoerfer <tsbogend@alpha.franken.de> | 2020-05-24 09:26:55 +0200 |
| commit | ec7a93188a75b57b9f704db6862e7137f01aa80b (patch) | |
| tree | 84907800878283ad5358796589613757ed9783f2 /arch/mips/Kconfig | |
| parent | 8267e78f020a8de2752754c42ec1d56e92431477 (diff) | |
| download | linux-ec7a93188a75b57b9f704db6862e7137f01aa80b.tar.gz linux-ec7a93188a75b57b9f704db6862e7137f01aa80b.tar.bz2 linux-ec7a93188a75b57b9f704db6862e7137f01aa80b.zip | |
MIPS: emulate CPUCFG instruction on older Loongson64 cores
CPUCFG is the instruction for querying processor characteristics on
newer Loongson processors, much like CPUID of x86. Since the instruction
is supposedly designed to provide a unified way to do feature detection
(without having to, for example, parse /proc/cpuinfo which is too
heavyweight), it is important to provide compatibility for older cores
without native support. Fortunately, most of the fields can be
synthesized without changes to semantics. Performance is not really big
a concern, because feature detection logic is not expected to be
invoked very often in typical userland applications.
The instruction can't be emulated on LOONGSON_2EF cores, according to
FlyGoat's experiments. Because the LWC2 opcode is assigned to other
valid instructions on 2E and 2F, no RI exception is raised for us to
intercept. So compatibility is only extended back furthest to
Loongson-3A1000. Loongson-2K is covered too, as it is basically a remix
of various blocks from the 3A/3B models from a kernel perspective.
This is lightly based on Loongson's work on their Linux 3.10 fork, for
being the authority on the right feature flags to fill in, where things
aren't otherwise discoverable.
Signed-off-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Diffstat (limited to 'arch/mips/Kconfig')
| -rw-r--r-- | arch/mips/Kconfig | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig index f347312ecd74..c5fe30c78402 100644 --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -1441,6 +1441,18 @@ config CPU_LOONGSON3_WORKAROUNDS If unsure, please say Y. +config CPU_LOONGSON3_CPUCFG_EMULATION + bool "Emulate the CPUCFG instruction on older Loongson cores" + default y + depends on CPU_LOONGSON64 + help + Loongson-3A R4 and newer have the CPUCFG instruction available for + userland to query CPU capabilities, much like CPUID on x86. This + option provides emulation of the instruction on older Loongson + cores, back to Loongson-3A1000. + + If unsure, please say Y. + config CPU_LOONGSON2E bool "Loongson 2E" depends on SYS_HAS_CPU_LOONGSON2E |