linux-kernel - Re: [PATCH v2] powerpc/kernel/sysfs: Export ldbar spr to sysfs

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Message-ID: <87h8ue960z.fsf@concordia.ellerman.id.au>
Date:   Wed, 01 Nov 2017 11:50:04 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Anju T Sudhakar <anju@...ux.vnet.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        maddy@...ux.vnet.ibm.com, anju@...ux.vnet.ibm.com
Subject: Re: [PATCH v2] powerpc/kernel/sysfs: Export ldbar spr to sysfs

Anju T Sudhakar <anju@...ux.vnet.ibm.com> writes:

> Add ldbar spr to sysfs. The spr will hold thread level In-Memory Collection (IMC)
> counter configuration data.

This is missing any justification for why we would want to expose this,
and in particular why we would make it *writable*.

cheers

> diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
> index 4437c70..f8caee0 100644
> --- a/arch/powerpc/kernel/sysfs.c
> +++ b/arch/powerpc/kernel/sysfs.c
> @@ -485,6 +485,7 @@ SYSFS_PMCSETUP(mmcra, SPRN_MMCRA);
>  SYSFS_SPRSETUP(purr, SPRN_PURR);
>  SYSFS_SPRSETUP(spurr, SPRN_SPURR);
>  SYSFS_SPRSETUP(pir, SPRN_PIR);
> +SYSFS_SPRSETUP(ldbar, SPRN_LDBAR);
>  
>  /*
>    Lets only enable read for phyp resources and
> @@ -492,6 +493,7 @@ SYSFS_SPRSETUP(pir, SPRN_PIR);
>    Lets be conservative and default to pseries.
>  */
>  static DEVICE_ATTR(mmcra, 0600, show_mmcra, store_mmcra);
> +static DEVICE_ATTR(ldbar, 0600, show_ldbar, store_ldbar);
>  static DEVICE_ATTR(spurr, 0400, show_spurr, NULL);
>  static DEVICE_ATTR(purr, 0400, show_purr, store_purr);
>  static DEVICE_ATTR(pir, 0400, show_pir, NULL);
> @@ -757,6 +759,9 @@ static int register_cpu_online(unsigned int cpu)
>  			device_create_file(s, &pmc_attrs[i]);
>  
>  #ifdef CONFIG_PPC64
> +	if (cpu_has_feature(CPU_FTR_ARCH_300))
> +		device_create_file(s, &dev_attr_ldbar);
> +
>  	if (cpu_has_feature(CPU_FTR_MMCRA))
>  		device_create_file(s, &dev_attr_mmcra);
>  
> @@ -842,6 +847,9 @@ static int unregister_cpu_online(unsigned int cpu)
>  			device_remove_file(s, &pmc_attrs[i]);
>  
>  #ifdef CONFIG_PPC64
> +	if (cpu_has_feature(CPU_FTR_ARCH_300))
> +		device_remove_file(s, &dev_attr_ldbar);
> +
>  	if (cpu_has_feature(CPU_FTR_MMCRA))
>  		device_remove_file(s, &dev_attr_mmcra);
>  
> -- 
> 2.7.4