linux-kernel - Re: [PATCH] ACPI/HMAT: Fix the parsing of Cache Associativity and Write Policy

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Date:   Tue, 10 Dec 2019 09:27:15 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Tao Xu <tao3.xu@...el.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Len Brown <lenb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ACPI/HMAT: Fix the parsing of Cache Associativity and
 Write Policy

On Tue, Dec 10, 2019 at 9:19 AM Tao Xu <tao3.xu@...el.com> wrote:
>
> On 12/10/2019 4:06 PM, Rafael J. Wysocki wrote:
> > On Tue, Dec 10, 2019 at 2:04 AM Tao Xu <tao3.xu@...el.com> wrote:
> >>
> >> On 12/9/2019 6:01 PM, Rafael J. Wysocki wrote:
> >>> On Mon, Dec 2, 2019 at 8:03 AM Tao Xu <tao3.xu@...el.com> wrote:
> >>>>
> >>>> In chapter 5.2.27.5, Table 5-147: Field "Cache Attributes" of
> >>>> ACPI 6.3 spec: 0 is "None", 1 is "Direct Mapped", 2 is "Complex Cache
> >>>> Indexing" for Cache Associativity; 0 is "None", 1 is "Write Back",
> >>>> 2 is "Write Through" for Write Policy.
> >>>
> >>> Well, I'm not sure what the connection between the above statement,
> >>> which is correct AFAICS, and the changes made by the patch is.
> >>>
> >>> Is that the *_OTHER symbol names are confusing or something deeper?
> >>>
> >>
> >> Because in include/acpi/actbl1.h:
> >>
> >> #define ACPI_HMAT_CA_NONE                     (0)
> >>
> >> ACPI_HMAT_CA_NONE is 0, but in include/linux/node.h:
> >>
> >>      enum cache_indexing {
> >>             NODE_CACHE_DIRECT_MAP,
> >>             NODE_CACHE_INDEXED,
> >>             NODE_CACHE_OTHER,
> >>      };
> >> NODE_CACHE_OTHER is 2, and for otner enum:
> >>
> >>            case ACPI_HMAT_CA_DIRECT_MAPPED:
> >>                    tcache->cache_attrs.indexing = NODE_CACHE_DIRECT_MAP;
> >>                    break;
> >>            case ACPI_HMAT_CA_COMPLEX_CACHE_INDEXING:
> >>                    tcache->cache_attrs.indexing = NODE_CACHE_INDEXED;
> >>                    break;
> >> in include/acpi/actbl1.h:
> >>
> >>    #define ACPI_HMAT_CA_DIRECT_MAPPED            (1)
> >>    #define ACPI_HMAT_CA_COMPLEX_CACHE_INDEXING   (2)
> >>
> >> but in include/linux/node.h:
> >>
> >> NODE_CACHE_DIRECT_MAP is 0, NODE_CACHE_INDEXED is 1. This is incorrect.
> >
> > Why is it incorrect?
>
> Sorry I paste the wrong pre-define.
>
> This is the incorrect line:
>
> case ACPI_HMAT_CA_DIRECT_MAPPED:
> tcache->cache_attrs.indexing = NODE_CACHE_DIRECT_MAP;
>
> ACPI_HMAT_CA_DIRECT_MAPPED is 1, NODE_CACHE_DIRECT_MAP is 0. That means
> if HMAT table input 1 for cache_attrs.indexing, kernel store 0 in
> cache_attrs.indexing. But in ACPI 6.3, 0 means "None". So for the whole
> switch codes:

This is a mapping between the ACPI-defined values and the generic ones
defined in the kernel.  There is not rule I know of by which they must
be the same numbers.  Or is there such a rule which I'm missing?

As long as cache_attrs.indexing is used consistently going forward,
the difference between the ACPI-defined numbers and its values
shouldn't matter, should it?

>
>          switch ((attrs & ACPI_HMAT_CACHE_ASSOCIATIVITY) >> 8) {
>          case ACPI_HMAT_CA_DIRECT_MAPPED(1):
>                  tcache->cache_attrs.indexing = NODE_CACHE_DIRECT_MAP(0);
>                  break;
>          case ACPI_HMAT_CA_COMPLEX_CACHE_INDEXING(2):
>                  tcache->cache_attrs.indexing = NODE_CACHE_INDEXED(1);
>                  break;
>          case ACPI_HMAT_CA_NONE(0):
>          default:
>                  tcache->cache_attrs.indexing = NODE_CACHE_OTHER(2);
>                  break;
>          }