linux-kernel - Re: [PATCH 1/3] powernv:idle: Use correct IDLE_THREAD

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Date:   Thu, 13 Apr 2017 16:36:20 +1000
From:   Michael Neuling <mikey@...ling.org>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        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>,
        Nicholas Piggin <npiggin@...il.com>,
        Mahesh J Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] powernv:idle: Use correct IDLE_THREAD_BITS in
 POWER8/9

On Wed, 2017-04-12 at 17:16 +0530, Gautham R. Shenoy wrote:
> From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
> 
> This patch ensures that POWER8 and POWER9 processors use the correct
> value of IDLE_THREAD_BITS as POWER8 has 8 threads per core and hence
> the IDLE_THREAD_BITS should be 0xFF while POWER9 has only 4 threads
> per core and hence the IDLE_THREAD_BITS should be 0xF.

Why don't we derive this from the device tree rather than hard wiring it per cpu
type?

Mikey

> 
> Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
> ---
>  arch/powerpc/include/asm/cpuidle.h    | 3 ++-
>  arch/powerpc/kernel/idle_book3s.S     | 9 ++++++---
>  arch/powerpc/platforms/powernv/idle.c | 5 ++++-
>  3 files changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/cpuidle.h
> b/arch/powerpc/include/asm/cpuidle.h
> index 52586f9..fece6ca 100644
> --- a/arch/powerpc/include/asm/cpuidle.h
> +++ b/arch/powerpc/include/asm/cpuidle.h
> @@ -34,7 +34,8 @@
>  #define PNV_CORE_IDLE_THREAD_WINKLE_BITS_SHIFT	8
>  #define PNV_CORE_IDLE_THREAD_WINKLE_BITS	0x0000FF00
>  
> -#define PNV_CORE_IDLE_THREAD_BITS       	0x000000FF
> +#define PNV_CORE_IDLE_4THREAD_BITS       	0x0000000F
> +#define PNV_CORE_IDLE_8THREAD_BITS       	0x000000FF
>  
>  /*
>   * ============================ NOTE =================================
> diff --git a/arch/powerpc/kernel/idle_book3s.S
> b/arch/powerpc/kernel/idle_book3s.S
> index 2b13fe2..9b747e9 100644
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -223,7 +223,7 @@ lwarx_loop1:
>  	add	r15,r15,r5			/* Add if winkle */
>  	andc	r15,r15,r7			/* Clear thread bit */
>  
> -	andi.	r9,r15,PNV_CORE_IDLE_THREAD_BITS
> +	andi.	r9,r15,PNV_CORE_IDLE_8THREAD_BITS
>  
>  /*
>   * If cr0 = 0, then current thread is the last thread of the core entering
> @@ -582,8 +582,11 @@ END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
>  	stwcx.	r15,0,r14
>  	bne-	1b
>  	isync
> -
> -	andi.	r9,r15,PNV_CORE_IDLE_THREAD_BITS
> +BEGIN_FTR_SECTION
> +	andi.	r9,r15,PNV_CORE_IDLE_4THREAD_BITS
> +FTR_SECTION_ELSE
> +	andi.	r9,r15,PNV_CORE_IDLE_8THREAD_BITS
> +ALT_FTR_SECTION_END_IFSET(CPU_FTR_ARCH_300)
>  	cmpwi	cr2,r9,0
>  
>  	/*
> diff --git a/arch/powerpc/platforms/powernv/idle.c
> b/arch/powerpc/platforms/powernv/idle.c
> index 445f30a..d46920b 100644
> --- a/arch/powerpc/platforms/powernv/idle.c
> +++ b/arch/powerpc/platforms/powernv/idle.c
> @@ -112,7 +112,10 @@ static void pnv_alloc_idle_core_states(void)
>  		size_t paca_ptr_array_size;
>  
>  		core_idle_state = kmalloc_node(sizeof(u32), GFP_KERNEL,
> node);
> -		*core_idle_state = PNV_CORE_IDLE_THREAD_BITS;
> +		if (cpu_has_feature(CPU_FTR_ARCH_300))
> +			*core_idle_state = PNV_CORE_IDLE_4THREAD_BITS;
> +		else
> +			*core_idle_state = PNV_CORE_IDLE_8THREAD_BITS;
>  		paca_ptr_array_size = (threads_per_core *
>  				       sizeof(struct paca_struct *));
>