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Date:   Wed, 8 Apr 2020 16:24:43 +0530
From:   Gautham R Shenoy <ego@linux.vnet.ibm.com>
To:     Pratik Rajesh Sampat <psampat@linux.ibm.com>
Cc:     linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org,
        mpe@ellerman.id.au, mikey@neuling.org, npiggin@gmail.com,
        vaidy@linux.ibm.com, ego@linux.vnet.ibm.com,
        skiboot@lists.ozlabs.org, oohall@gmail.com,
        pratik.r.sampat@gmail.com
Subject: Re: [RFC 3/3] Introduce capability for firmware-enabled-stop
Message-ID: <20200408105443.GE950@in.ibm.com>
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References: <cover.1583332695.git.psampat@linux.ibm.com>
 <55fa5021e4de901f05ded8b669777711bf2a9724.1583332695.git.psampat@linux.ibm.com>
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Hi Pratik,

On Wed, Mar 04, 2020 at 09:31:23PM +0530, Pratik Rajesh Sampat wrote:
> Design patch that introduces the capability for firmware to handle the
> stop states instead. A bit is set based on the discovery of the feature
> and correspondingly also the responsibility to handle the stop states.
> 
> The commit does not contain calling into the firmware to utilize
> firmware enabled stop.
> 
> Signed-off-by: Pratik Rajesh Sampat <psampat at linux.ibm.com>
> ---
>  arch/powerpc/include/asm/processor.h | 1 +
>  arch/powerpc/kernel/dt_cpu_ftrs.c    | 9 +++++++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
> index 277dbabafd02..978fab35d133 100644
> --- a/arch/powerpc/include/asm/processor.h
> +++ b/arch/powerpc/include/asm/processor.h
> @@ -430,6 +430,7 @@ extern unsigned long cpuidle_disable;
>  enum idle_boot_override {IDLE_NO_OVERRIDE = 0, IDLE_POWERSAVE_OFF};
> 
>  #define STOP_ENABLE		0x00000001
> +#define FIRMWARE_STOP_ENABLE	0x00000010


This could be made a bit in the "version" variable.

> 
>  #define STOP_VERSION_P9       0x1
>  #define STOP_VERSION_P9_V1    0x2
> diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
> index 63e30aa49356..e00f8afabc46 100644
> --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
> +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
> @@ -313,6 +313,14 @@ static int __init feat_enable_idle_stop_quirk(struct dt_cpu_feature *f)
> 
>  	return 1;
>  }
> +
> +static int __init feat_enable_firmware_stop(struct dt_cpu_feature *f)
> +{
> +	stop_dep.cpuidle_prop |= FIRMWARE_STOP_ENABLE;

  	stop_dep.cpuidle_version |= FIRMWARE_STOP_V1; or some such
  	variant.


> +
> +	return 1;
> +}
> +
>  static int __init feat_enable_mmu_hash(struct dt_cpu_feature *f)
>  {
>  	u64 lpcr;
> @@ -608,6 +616,7 @@ static struct dt_cpu_feature_match __initdata
>  	{"alignment-interrupt-dsisr", feat_enable_align_dsisr, 0},
>  	{"idle-stop", feat_enable_idle_stop, 0},
>  	{"idle-stop-v1", feat_enable_idle_stop_quirk, 0},
> +	{"firmware-stop-supported", feat_enable_firmware_stop, 0},
>  	{"machine-check-power8", feat_enable_mce_power8, 0},
>  	{"performance-monitor-power8", feat_enable_pmu_power8, 0},
>  	{"data-stream-control-register", feat_enable_dscr, CPU_FTR_DSCR},
> -- 
> 2.24.1
>