linux-kernel - Re: [RFC v2 2/5] acpi: HMAT support in acpi_parse_entries

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Date:   Thu, 6 Jul 2017 16:22:00 -0600
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Anaczkowski, Lukasz" <lukasz.anaczkowski@...el.com>,
        "Box, David E" <david.e.box@...el.com>,
        "Kogut, Jaroslaw" <Jaroslaw.Kogut@...el.com>,
        "Lahtinen, Joonas" <joonas.lahtinen@...el.com>,
        "Moore, Robert" <robert.moore@...el.com>,
        "Nachimuthu, Murugasamy" <murugasamy.nachimuthu@...el.com>,
        "Odzioba, Lukasz" <lukasz.odzioba@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Schmauss, Erik" <erik.schmauss@...el.com>,
        "Verma, Vishal L" <vishal.l.verma@...el.com>,
        "Zheng, Lv" <lv.zheng@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jerome Glisse <jglisse@...hat.com>,
        Len Brown <lenb@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "devel@...ica.org" <devel@...ica.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: Re: [RFC v2 2/5] acpi: HMAT support in acpi_parse_entries_array()

On Fri, Jul 07, 2017 at 12:13:54AM +0200, Rafael J. Wysocki wrote:
> On Thu, Jul 6, 2017 at 11:52 PM, Ross Zwisler
> <ross.zwisler@...ux.intel.com> wrote:
> > The current implementation of acpi_parse_entries_array() assumes that each
> > subtable has a standard ACPI subtable entry of type struct
> > acpi_sutbable_header.  This standard subtable header has a one byte length
> > followed by a one byte type.
> >
> > The HMAT subtables have to allow for a longer length so they have subtable
> > headers of type struct acpi_hmat_structure which has a 2 byte type and a 4
> > byte length.
> >
> > Enhance the subtable parsing in acpi_parse_entries_array() so that it can
> > handle these new HMAT subtables.
> >
> > Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> > ---
> >  drivers/acpi/numa.c   |  2 +-
> >  drivers/acpi/tables.c | 52 ++++++++++++++++++++++++++++++++++++++++-----------
> >  2 files changed, 42 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/acpi/numa.c b/drivers/acpi/numa.c
> > index edb0c79..917f1cc 100644
> > --- a/drivers/acpi/numa.c
> > +++ b/drivers/acpi/numa.c
> > @@ -443,7 +443,7 @@ int __init acpi_numa_init(void)
> >          * So go over all cpu entries in SRAT to get apicid to node mapping.
> >          */
> >
> > -       /* SRAT: Static Resource Affinity Table */
> > +       /* SRAT: System Resource Affinity Table */
> >         if (!acpi_table_parse(ACPI_SIG_SRAT, acpi_parse_srat)) {
> >                 struct acpi_subtable_proc srat_proc[3];
> >
> 
> This change is unrelated to the rest of the patch.
> 
> Maybe send it separately?

Sure, will do.

> > diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
> > index ff42539..7979171 100644
> > --- a/drivers/acpi/tables.c
> > +++ b/drivers/acpi/tables.c
> > @@ -218,6 +218,33 @@ void acpi_table_print_madt_entry(struct acpi_subtable_header *header)
> >         }
> >  }
> >
> > +static unsigned long __init
> > +acpi_get_entry_type(char *id, void *entry)
> > +{
> > +       if (!strncmp(id, ACPI_SIG_HMAT, 4))
> > +               return ((struct acpi_hmat_structure *)entry)->type;
> > +       else
> > +               return ((struct acpi_subtable_header *)entry)->type;
> > +}
> 
> I slightly prefer to use ? : in similar situations.

Hmm..that becomes rather long, and seems complex for the already hard to read
?: operator?  Let's see, this:

	if (!strncmp(id, ACPI_SIG_HMAT, 4))
		return ((struct acpi_hmat_structure *)entry)->type;
	else
		return ((struct acpi_subtable_header *)entry)->type;

becomes

	return strncmp(id, ACPI_SIG_HMAT, 4)) ?
		((struct acpi_subtable_header *)entry)->type :
		((struct acpi_hmat_structure *)entry)->type;

Hmm...we only save one line, and I personally find that a lot harder to read,
but that being said if you feel strongly about it I'll make the change.