linux-kernel - Re: [PATCH] ACPI/PPTT: Handle architecturally unknown cache types

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Date:   Wed, 12 Sep 2018 10:25:47 -0600
From:   Jeffrey Hugo <jhugo@...eaurora.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Jeremy Linton <jeremy.linton@....com>, rjw@...ysocki.net,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        vkilari@...eaurora.org
Subject: Re: [PATCH] ACPI/PPTT: Handle architecturally unknown cache types

On 9/12/2018 10:15 AM, Sudeep Holla wrote:
> On Wed, Sep 12, 2018 at 09:57:14AM -0600, Jeffrey Hugo wrote:
>> On 9/12/2018 9:38 AM, Sudeep Holla wrote:
>>>
>>>
>>> On 12/09/18 16:27, Sudeep Holla wrote:
>>>>
>>>>
>>>> On 12/09/18 15:41, Jeffrey Hugo wrote:
>>>
>>> [...]
>>>
>>>>>
>>>>> Correct.  However, what if you have a NOCACHE (not architecturally
>>>>> specified), that is fully described in PPTT, as a non-unified cache
>>>>> (data only)?  Unlikely?  Maybe.  Still seem possible though, therefore I
>>>>> feel this assumption is suspect.
>>>>>
>>>>
>>>> Yes, we have other issues if the architecturally not specified cache is
>>>> not unified irrespective of what PPTT says. So we may need to review and
>>>> see if that assumption is removed everywhere.
>>>>
>>>> Until then why can't a simple change fix the issue you have:
>>>>
>>>> -->8
>>>>
>>>> diff --git i/drivers/acpi/pptt.c w/drivers/acpi/pptt.c
>>>> index d1e26cb599bf..f74131201f5e 100644
>>>> --- i/drivers/acpi/pptt.c
>>>> +++ w/drivers/acpi/pptt.c
>>>> @@ -406,7 +406,8 @@ static void update_cache_properties(struct cacheinfo
>>>> *this_leaf,
>>>>           * update the cache type as well.
>>>>           */
>>>>          if (this_leaf->type == CACHE_TYPE_NOCACHE &&
>>>> -           valid_flags == PPTT_CHECKED_ATTRIBUTES)
>>>> +           (valid_flags == PPTT_CHECKED_ATTRIBUTES ||
>>>> +            found_cache->flags & ACPI_PPTT_CACHE_TYPE_VALID))
>>>
>>> Looking at this again, if we are supporting just presence of cache type
>>> and size(may be), then we can drop the whole valid_flags thing here.
>>>
>>>>                  this_leaf->type = CACHE_TYPE_UNIFIED;
>>>>   }
>>>>
>>
>> Yes, this change fixes my usecase.  I think it invalidates the comment, and
>> really, the comment should probably mention that we assume unified type
>> because there are other issues in supporting architecturally not specified
>> inst/data only caches.
>>
> 
> Agreed.
> 
>> Do you want a V2 with this?  If so, do you want the fixes tag removed since
>> you seem to view this as not a bug?
>>
> 
> Yes please, I am fine to retain fixes tag but that's my opinion.
> 
>> I don't think I clearly understand the purpose of the valid flags, therefore
>> I feel as though I'm not sure if it can be dropped or not.  Is it fair to
>> say that what the valid flags is accomplishing is identifying if we have a
>> sufficient level of information to support this cache?  If not, then should
>> the cacheinfo driver not expose any sysfs information about the cache?
>>
> 
> I don't see the use of the flag if we *have to* support the case where
> all the cache geometry is not present but just cache type (and maybe
> size?) is present. If that's the case we can drop valid flags entirely.
> I really don't like the idea of supporting that, but I don't have strong
> reasons to defend my idea, so I am fine with that.
> 
> Further, I think in your case with NOCACHE type set, sysfs dir shouldn't
> have been created at the first place ideally. I think we need something
> like below to fix that.
> 
> -->8
> 
> diff --git i/drivers/base/cacheinfo.c w/drivers/base/cacheinfo.c
> index 5d5b5988e88b..cf78fa6d470d 100644
> --- i/drivers/base/cacheinfo.c
> +++ w/drivers/base/cacheinfo.c
> @@ -615,6 +615,8 @@ static int cache_add_dev(unsigned int cpu)
>   		this_leaf = this_cpu_ci->info_list + i;
>   		if (this_leaf->disable_sysfs)
>   			continue;
> +		if (this_leaf->type == CACHE_TYPE_NOCACHE)
> +			break;
>   		cache_groups = cache_get_attribute_groups(this_leaf);
>   		ci_dev = cpu_device_create(parent, this_leaf, cache_groups,
>   					   "index%1u", i);
> 

Ok, let me test this out, and send out a v2.

-- 
Jeffrey Hugo
Qualcomm Datacenter Technologies as an affiliate of Qualcomm 
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.