linux-kernel - Re: [PATCH] LoongArch: Clean useless vcsr in loongarch

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Date:   Mon, 4 Jul 2022 17:27:13 +0800
From:   huqi <huqi@...ngson.cn>
To:     WANG Xuerui <kernel@...0n.name>,
        Huacai Chen <chenhuacai@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: Clean useless vcsr in loongarch_fpu.


On 2022/7/4 15:28, WANG Xuerui wrote:
> On 2022/7/4 14:14, huqi wrote:
>> From: Qi Hu <huqi@...ngson.cn>
>>
>> The `vcsr` do not use anymore. Remove this member from `loongarch_fpu`.
> "The VCSR is not used any more."
Thanks, this is incorrect to use `use`.
>>
>> Signed-off-by: Qi Hu <huqi@...ngson.cn>
>> ---
>>   arch/loongarch/include/asm/fpregdef.h  |  1 -
>>   arch/loongarch/include/asm/processor.h |  2 --
>>   arch/loongarch/kernel/asm-offsets.c    |  1 -
>>   arch/loongarch/kernel/fpu.S            | 10 ----------
>>   4 files changed, 14 deletions(-)
>>
>> diff --git a/arch/loongarch/include/asm/fpregdef.h 
>> b/arch/loongarch/include/asm/fpregdef.h
>> index adb16e4b43b0..b6be527831dd 100644
>> --- a/arch/loongarch/include/asm/fpregdef.h
>> +++ b/arch/loongarch/include/asm/fpregdef.h
>> @@ -48,6 +48,5 @@
>>   #define fcsr1    $r1
>>   #define fcsr2    $r2
>>   #define fcsr3    $r3
>> -#define vcsr16    $r16
>>     #endif /* _ASM_FPREGDEF_H */
>> diff --git a/arch/loongarch/include/asm/processor.h 
>> b/arch/loongarch/include/asm/processor.h
>> index 1d63c934b289..57ec45aa078e 100644
>> --- a/arch/loongarch/include/asm/processor.h
>> +++ b/arch/loongarch/include/asm/processor.h
>> @@ -80,7 +80,6 @@ BUILD_FPR_ACCESS(64)
>>     struct loongarch_fpu {
>>       unsigned int    fcsr;
>> -    unsigned int    vcsr;
>>       uint64_t    fcc;    /* 8x8 */
>>       union fpureg    fpr[NUM_FPU_REGS];
>>   };
>> @@ -161,7 +160,6 @@ struct thread_struct {
>>        */                            \
>>       .fpu            = {                \
>>           .fcsr        = 0,                \
>> -        .vcsr        = 0,                \
>>           .fcc        = 0,                \
>>           .fpr        = {{{0,},},},            \
>>       },                            \
>> diff --git a/arch/loongarch/kernel/asm-offsets.c 
>> b/arch/loongarch/kernel/asm-offsets.c
>> index bfb65eb2844f..20cd9e16a95a 100644
>> --- a/arch/loongarch/kernel/asm-offsets.c
>> +++ b/arch/loongarch/kernel/asm-offsets.c
>> @@ -166,7 +166,6 @@ void output_thread_fpu_defines(void)
>>         OFFSET(THREAD_FCSR, loongarch_fpu, fcsr);
>>       OFFSET(THREAD_FCC,  loongarch_fpu, fcc);
>> -    OFFSET(THREAD_VCSR, loongarch_fpu, vcsr);
>>       BLANK();
>>   }
>>   diff --git a/arch/loongarch/kernel/fpu.S b/arch/loongarch/kernel/fpu.S
>> index 75c6ce0682a2..a631a7137667 100644
>> --- a/arch/loongarch/kernel/fpu.S
>> +++ b/arch/loongarch/kernel/fpu.S
>> @@ -146,16 +146,6 @@
>>       movgr2fcsr    fcsr0, \tmp0
>>       .endm
>>   -    .macro sc_save_vcsr base, tmp0
>> -    movfcsr2gr    \tmp0, vcsr16
>> -    EX    st.w \tmp0, \base, 0
>> -    .endm
>> -
>> -    .macro sc_restore_vcsr base, tmp0
>> -    EX    ld.w \tmp0, \base, 0
>> -    movgr2fcsr    vcsr16, \tmp0
>> -    .endm
>> -
>>   /*
>>    * Save a thread's fp context.
>>    */
>
> The original code was written with future LSX/LASX support in mind; 
> the code is dead currently, but expected to get utilized Soon (TM).
>
> So, I'd like to confirm if future LoongArch models would *not* feature 
> LSX/LASX in its current form, and that the Loongson Corporation is not 
> going to upstream LSX/LASX support, given you are apparently a 
> Loongson employee with the first-hand information? We'd like to avoid 
> code churn in general, so if the LSX/LASX support is to be eventually 
> mainlined, removing them now would only lead to them being introduced 
> later.

`vcsr` is removed because it has been removed in hardware. What's more, 
it will not be used to support LSX/LASX in the future.