Re: [PATCH 1/2] riscv: Add stimecmp save and restore

From: Andrew Jones <ajones@ventanamicro.com>
To: Nick Hu <nick.hu@sifive.com>
Cc: greentime.hu@sifive.com, zong.li@sifive.com,
	 "Rafael J. Wysocki" <rafael@kernel.org>,
	Pavel Machek <pavel@ucw.cz>,
	 Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	 Albert Ou <aou@eecs.berkeley.edu>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	 Thomas Gleixner <tglx@linutronix.de>,
	Conor Dooley <conor.dooley@microchip.com>,
	 Samuel Holland <samuel.holland@sifive.com>,
	Sunil V L <sunilvl@ventanamicro.com>,
	linux-pm@vger.kernel.org,  linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] riscv: Add stimecmp save and restore
Date: Thu, 29 Aug 2024 09:59:04 +0200	[thread overview]
Message-ID: <20240829-fb7bda6b46302b65b2f89d20@orel> (raw)
In-Reply-To: <20240829033904.477200-2-nick.hu@sifive.com>

On Thu, Aug 29, 2024 at 11:38:59AM GMT, Nick Hu wrote:
> If the HW support the SSTC extension, we should save and restore the
> stimecmp register while cpu non retention suspend.
> 
> Signed-off-by: Nick Hu <nick.hu@sifive.com>
> ---
>  arch/riscv/include/asm/suspend.h |  4 ++++
>  arch/riscv/kernel/suspend.c      | 13 +++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/suspend.h b/arch/riscv/include/asm/suspend.h
> index 4ffb022b097f..ffaac2efabb5 100644
> --- a/arch/riscv/include/asm/suspend.h
> +++ b/arch/riscv/include/asm/suspend.h
> @@ -16,6 +16,10 @@ struct suspend_context {
>  	unsigned long envcfg;
>  	unsigned long tvec;
>  	unsigned long ie;
> +#if __riscv_xlen < 64
> +	unsigned long stimecmph;
> +#endif

I'm not sure the reduction in struct size is worth the #ifdeffery. If we
just always add stimecmph, then we can also change the #ifdef's below to
if's, i.e. if (__riscv_xlen < 64), which should still remove the code from
64-bit builds.

Or maybe we need something like

#if __riscv_xlen < 64
#define csrh_write(r, v) csr_write(r, v)
#else
#define csrh_write(r, v)
#endif

in asm/csr.h and then use it for all the *h csrs, but keep the #if in
the struct.

Thanks,
drew

> +	unsigned long stimecmp;
>  #ifdef CONFIG_MMU
>  	unsigned long satp;
>  #endif
> diff --git a/arch/riscv/kernel/suspend.c b/arch/riscv/kernel/suspend.c
> index c8cec0cc5833..3afd86e1abf7 100644
> --- a/arch/riscv/kernel/suspend.c
> +++ b/arch/riscv/kernel/suspend.c
> @@ -19,6 +19,12 @@ void suspend_save_csrs(struct suspend_context *context)
>  	context->tvec = csr_read(CSR_TVEC);
>  	context->ie = csr_read(CSR_IE);
>  
> +	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SSTC)) {
> +		context->stimecmp = csr_read(CSR_STIMECMP);
> +#if __riscv_xlen < 64
> +		context->stimecmph = csr_read(CSR_STIMECMPH);
> +#endif
> +	}
>  	/*
>  	 * No need to save/restore IP CSR (i.e. MIP or SIP) because:
>  	 *
> @@ -42,6 +48,13 @@ void suspend_restore_csrs(struct suspend_context *context)
>  	csr_write(CSR_TVEC, context->tvec);
>  	csr_write(CSR_IE, context->ie);
>  
> +	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SSTC)) {
> +		csr_write(CSR_STIMECMP, context->stimecmp);
> +#if __riscv_xlen < 64
> +		csr_write(CSR_STIMECMPH, context->stimecmph);
> +#endif
> +	}
> +
>  #ifdef CONFIG_MMU
>  	csr_write(CSR_SATP, context->satp);
>  #endif
> -- 
> 2.34.1
> 