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

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Message-ID: <c835027a-9e3e-221b-01da-0e1930c4e58f@codeaurora.org>
Date:   Wed, 12 Sep 2018 09:57:14 -0600
From:   Jeffrey Hugo <jhugo@...eaurora.org>
To:     Sudeep Holla <sudeep.holla@....com>,
        Jeremy Linton <jeremy.linton@....com>, rjw@...ysocki.net,
        linux-acpi@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, vkilari@...eaurora.org
Subject: Re: [PATCH] ACPI/PPTT: Handle architecturally unknown cache types

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.

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?

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?

-- 
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.