Re: [PATCH V7 2/3] MIPS: Loongson-3: Enable COP2 usage in kernel

From: Jiaxun Yang <jiaxun.yang@flygoat.com>
To: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Huacai Chen <chenhc@lemote.com>
Cc: linux-mips@vger.kernel.org, Fuxin Zhang <zhangfx@lemote.com>,
	Huacai Chen <chenhuacai@gmail.com>
Subject: Re: [PATCH V7 2/3] MIPS: Loongson-3: Enable COP2 usage in kernel
Date: Wed, 23 Sep 2020 17:44:02 +0800	[thread overview]
Message-ID: <177ADF0C-1633-449F-B589-712EA4857E79@flygoat.com> (raw)
In-Reply-To: <20200921121554.GA8642@alpha.franken.de>

于 2020年9月21日 GMT+08:00 下午8:15:54, Thomas Bogendoerfer <tsbogend@alpha.franken.de> 写到:
>On Mon, Sep 21, 2020 at 05:12:27PM +0800, Huacai Chen wrote:
>> Loongson-3's COP2 is Multi-Media coprocessor, it is disabled in kernel
>> mode by default. However, gslq/gssq (16-bytes load/store instructions)
>> overrides the instruction format of lwc2/swc2. If we wan't to use gslq/
>> gssq for optimization in kernel, we should enable COP2 usage in kernel.
>> 
>> Please pay attention that in this patch we only enable COP2 in kernel,
>> which means it will lose ST0_CU2 when a process go to user space (try
>> to use COP2 in user space will trigger an exception and then grab COP2,
>> which is similar to FPU). And as a result, we need to modify the context
>> switching code because the new scheduled process doesn't contain ST0_CU2
>> in its THERAD_STATUS probably.
>> 
>> For zboot, we disable gslq/gssq be generated by toolchain.
>> 
>> Signed-off-by: Huacai Chen <chenhc@lemote.com>
>> ---
>> V3: Stop using ST0_MM and use ST0_CU2 instead (Thank Thomas and Maciej).
>> V4: Adopt Thomas's suggestion to improve coding style.
>> V5: Use ST0_KERNEL_CUMASK in all possible places to avoid #ifdefs.
>> V6: Modify switch_to() and don't touch r4k_switch.S.
>> V7: For zboot, disable gslq/gssq be generated by toolchain.
>> 
>>  arch/mips/boot/compressed/Makefile | 5 +++++
>>  arch/mips/include/asm/mipsregs.h   | 7 +++++++
>>  arch/mips/include/asm/stackframe.h | 6 +++---
>>  arch/mips/kernel/head.S            | 2 +-
>>  arch/mips/kernel/process.c         | 4 ++--
>>  arch/mips/kernel/traps.c           | 2 +-
>>  6 files changed, 19 insertions(+), 7 deletions(-)
>> 
>> diff --git a/arch/mips/boot/compressed/Makefile b/arch/mips/boot/compressed/Makefile
>> index 9a9ba77..2c491c1 100644
>> --- a/arch/mips/boot/compressed/Makefile
>> +++ b/arch/mips/boot/compressed/Makefile
>> @@ -22,6 +22,11 @@ KBUILD_CFLAGS := $(filter-out -pg, $(KBUILD_CFLAGS))
>>  
>>  KBUILD_CFLAGS := $(filter-out -fstack-protector, $(KBUILD_CFLAGS))
>>  
>> +# Disable lq/sq in zboot
>> +ifdef CONFIG_CPU_LOONGSON64
>> +KBUILD_CFLAGS := $(filter-out -march=loongson3a, $(KBUILD_CFLAGS)) -march=mips64r2
>> +endif
>> +
>
>thanks for doing this, I'm going to apply this later.
>
>This remind of another question, what about loongson2ef ? I'm getting
>kbuild failure because of enabled loongson-mmi mails. Are we are missing
>something like cflags-y += $(call cc-option,-mno-loongson-mmi) in Platform
>file ? Who is taking care of loongson2ef ?

I'll send a patch later. Sorry for the inconvenience.

I'm taking care of it. Just being a little bit busy recently.

Thanks.

- Jiaxun

>
>Thomas.
>