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

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Date:   Mon, 4 Jul 2022 15:28:01 +0800
From:   WANG Xuerui <kernel@...0n.name>
To:     huqi <huqi@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        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 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."
>
> 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.