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SubjectRe: [PATCH] ACPI/PPTT: Handle architecturally unknown cache types
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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.

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