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SubjectRe: [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.

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