linux-kernel - Re: [PATCH] Delete some unusefull operations for centaur CPU/platform

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Message-ID: <1983196.2xaV79s388@aspire.rjw.lan>
Date:   Fri, 02 Mar 2018 12:31:34 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     David Wang <davidwang@...oxin.com>
Cc:     len.brown@...el.com, pavel@....cz, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        linux-pm@...nel.org, linux-kernel@...r.kernel.org,
        brucechang@...-alliance.com, cooperyan@...oxin.com,
        qiyuanwang@...oxin.com, benjaminpan@...tech.com,
        lukelin@...cpu.com, timguo@...oxin.com, cobechen@...oxin.com,
        jiangbowang@...oxin.com
Subject: Re: [PATCH] Delete some unusefull operations for centaur CPU/platform

On Friday, March 2, 2018 5:11:48 AM CET David Wang wrote:
> For Centaur CPU, the ucode will make sure that each CPU core can keep cache
> coherency with each other when the CPU core entering to any C state. So the
> cache flush operations when enter C3 is not necessary and will cause large
> C3 enter/exit latency.
> And the bus master disable operation when CPU core entering C3 state is not
> needed too. Because the chipset will automatically do this operation.
> 
> Signed-off-by: David Wang <davidwang@...oxin.com>

I've queued up the previous version of your patch with some changes to
comments/subject/changelog made by me for v4.17.

Please see linux-next.

> ---
>  arch/x86/kernel/acpi/cstate.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
> index dde437f..1cd357b 100644
> --- a/arch/x86/kernel/acpi/cstate.c
> +++ b/arch/x86/kernel/acpi/cstate.c
> @@ -51,6 +51,18 @@ void acpi_processor_power_init_bm_check(struct acpi_processor_flags *flags,
>  	if (c->x86_vendor == X86_VENDOR_INTEL &&
>  	    (c->x86 > 0xf || (c->x86 == 6 && c->x86_model >= 0x0f)))
>  			flags->bm_control = 0;
> +
> +        if (c->x86_vendor == X86_VENDOR_CENTAUR) {
> +		/*
> +		 * on all centaur CPUs, sw need not execute cache flush operation
> +		 * when entering C3 type State.
> +		 *
> +		 * On all Centaur platforms, sw need not execute ARB_DISABLE while
> +		 * entering C3 type state.
> +		 */
> +		flags->bm_check = 1;
> +		flags->bm_control = 0;
> +	}
>  }
>  EXPORT_SYMBOL(acpi_processor_power_init_bm_check);
>  
>