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

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Date:   Fri, 7 Jul 2017 00:36:16 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        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 7, 2017 at 12:22 AM, Ross Zwisler
<ross.zwisler@...ux.intel.com> wrote:
> 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(-)

[cut]

>> > 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.

Well, I said "slightly". :-)

Thanks,
Rafael