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

[Jeffrey Hugo]

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.