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

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Message-Id: <48d62ebb-73b9-86c6-b1f2-39ee1d3ae846@linux.vnet.ibm.com>
Date:   Tue, 7 Nov 2017 17:36:08 +0530
From:   Anju T Sudhakar <anju@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        maddy@...ux.vnet.ibm.com
Subject: Re: [PATCH v2] powerpc/kernel/sysfs: Export ldbar spr to sysfs

Hi mpe,


On Wednesday 01 November 2017 06:20 AM, Michael Ellerman wrote:
> 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


Thank you for reviewing the patch.

LDBAR, holds the thread-level counter configuration. Exposing this will help
us to understand  the current status of thread-level counters in the system.
Primarily, Bit 0 of ldbar tells whether the counters are enabled or not.
And bit 1  tells the mode (if 0-Accumulation Mode/if 1-Trace Mode).

But regarding the permission, you are right. On a reassessment I think 
that the permission
should be read only, because it is possible that we may write an 
incorrect value to the ldbar, that is wrong.
So I will change the permission here.



Thanks,
Anju
>
>> 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