Re: [PATCH] riscv: Do not save the scratch CSR during suspend

From: Andrew Jones <ajones@ventanamicro.com>
To: Samuel Holland <samuel.holland@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>,
	linux-riscv@lists.infradead.org,
	 Albert Ou <aou@eecs.berkeley.edu>,
	Conor Dooley <conor.dooley@microchip.com>,
	 Ley Foon Tan <leyfoon.tan@starfivetech.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	 Pavel Machek <pavel@ucw.cz>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	 Sia Jee Heng <jeeheng.sia@starfivetech.com>,
	linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH] riscv: Do not save the scratch CSR during suspend
Date: Wed, 13 Mar 2024 09:44:18 +0100	[thread overview]
Message-ID: <20240313-a1837dd45cb20198ef5ceae6@orel> (raw)
In-Reply-To: <20240312195641.1830521-1-samuel.holland@sifive.com>

On Tue, Mar 12, 2024 at 12:56:38PM -0700, Samuel Holland wrote:
> While the processor is executing kernel code, the value of the scratch
> CSR is always zero, so there is no need to save the value. Continue to
> write the CSR during the resume flow, so we do not rely on firmware to
> initialize it.
> 
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
> ---
> 
>  arch/riscv/include/asm/suspend.h | 1 -
>  arch/riscv/kernel/suspend.c      | 3 +--
>  2 files changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/suspend.h b/arch/riscv/include/asm/suspend.h
> index 491296a335d0..6569eefacf38 100644
> --- a/arch/riscv/include/asm/suspend.h
> +++ b/arch/riscv/include/asm/suspend.h
> @@ -13,7 +13,6 @@ struct suspend_context {
>  	/* Saved and restored by low-level functions */
>  	struct pt_regs regs;
>  	/* Saved and restored by high-level functions */
> -	unsigned long scratch;
>  	unsigned long envcfg;
>  	unsigned long tvec;
>  	unsigned long ie;
> diff --git a/arch/riscv/kernel/suspend.c b/arch/riscv/kernel/suspend.c
> index 299795341e8a..3d306d8a253d 100644
> --- a/arch/riscv/kernel/suspend.c
> +++ b/arch/riscv/kernel/suspend.c
> @@ -14,7 +14,6 @@
>  
>  void suspend_save_csrs(struct suspend_context *context)
>  {
> -	context->scratch = csr_read(CSR_SCRATCH);
>  	if (riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_XLINUXENVCFG))
>  		context->envcfg = csr_read(CSR_ENVCFG);
>  	context->tvec = csr_read(CSR_TVEC);
> @@ -37,7 +36,7 @@ void suspend_save_csrs(struct suspend_context *context)
>  
>  void suspend_restore_csrs(struct suspend_context *context)
>  {
> -	csr_write(CSR_SCRATCH, context->scratch);
> +	csr_write(CSR_SCRATCH, 0);
>  	if (riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_XLINUXENVCFG))
>  		csr_write(CSR_ENVCFG, context->envcfg);
>  	csr_write(CSR_TVEC, context->tvec);
> -- 
> 2.43.1
>

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

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