linux-kernel - Re: [v2 PATCH 3/4] powernv:idle: Don't override default/deepest directly in kernel

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Date:   Tue, 21 Mar 2017 02:39:34 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Michael Neuling <mikey@...ling.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        "Shreyas B. Prabhu" <shreyasbp@...il.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Anton Blanchard <anton@...ba.org>,
        Balbir Singh <bsingharora@...il.com>,
        Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH 3/4] powernv:idle: Don't override default/deepest
 directly in kernel

On Mon, 20 Mar 2017 21:24:17 +0530
"Gautham R. Shenoy" <ego@...ux.vnet.ibm.com> wrote:

> From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
> 
> Currently during idle-init on power9, if we don't find suitable stop
> states in the device tree that can be used as the
> default_stop/deepest_stop, we set stop0 (ESL=1,EC=1) as the default
> stop state psscr to be used by power9_idle and deepest stop state
> which is used by CPU-Hotplug.
> 
> However, if the platform firmware has not configured or enabled a stop
> state, the kernel should not make any assumptions and fallback to a
> default choice.
> 
> If the kernel uses a stop state that is not configured by the platform
> firmware, it may lead to further failures which should be avoided.
> 
> In this patch, we modify the init code to ensure that the kernel uses
> only the stop states exposed by the firmware through the device
> tree. When a suitable default stop state isn't found, we disable
> ppc_md.power_save for power9. Similarly, when a suitable
> deepest_stop_state is not found in the device tree exported by the
> firmware, fall back to the default busy-wait loop in the CPU-Hotplug
> code.
> 
> [Changelog written with inputs from svaidy@...ux.vnet.ibm.com]
> 
> Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
> ---
>  arch/powerpc/platforms/powernv/idle.c | 35 ++++++++++++++++++-----------------
>  1 file changed, 18 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
> index f335e0f..63ade78 100644
> --- a/arch/powerpc/platforms/powernv/idle.c
> +++ b/arch/powerpc/platforms/powernv/idle.c
> @@ -147,7 +147,6 @@ u32 pnv_get_supported_cpuidle_states(void)
>  }
>  EXPORT_SYMBOL_GPL(pnv_get_supported_cpuidle_states);
>  
> -
>  static void pnv_fastsleep_workaround_apply(void *info)
>  
>  {
> @@ -241,8 +240,9 @@ static DEVICE_ATTR(fastsleep_workaround_applyonce, 0600,
>   * The default stop state that will be used by ppc_md.power_save
>   * function on platforms that support stop instruction.
>   */
> -u64 pnv_default_stop_val;
> -u64 pnv_default_stop_mask;
> +static u64 pnv_default_stop_val;
> +static u64 pnv_default_stop_mask;
> +static bool default_stop_found;
>  
>  /*
>   * Used for ppc_md.power_save which needs a function with no parameters
> @@ -262,8 +262,9 @@ static void power9_idle(void)
>   * psscr value and mask of the deepest stop idle state.
>   * Used when a cpu is offlined.
>   */
> -u64 pnv_deepest_stop_psscr_val;
> -u64 pnv_deepest_stop_psscr_mask;
> +static u64 pnv_deepest_stop_psscr_val;
> +static u64 pnv_deepest_stop_psscr_mask;
> +static bool deepest_stop_found;

Aha you have made them static. Nitpick withdrawn :)

The log messages look good now.

Reviewed-by: Nicholas Piggin <npiggin@...il.com>