Re: [PATCH v3 1/3] acpi: HMAT support in acpi_parse_entries_array()

[Rafael J. Wysocki]

On Sat, Dec 16, 2017 at 2:57 AM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> On Fri, Dec 15, 2017 at 5:53 PM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
>> On Friday, December 15, 2017 2:10:17 AM CET Dan Williams wrote:
>>> On Wed, Dec 13, 2017 at 6:10 PM, Ross Zwisler
>>> <ross.zwisler@xxxxxxxxxxxxxxx> wrote:
>>> > The current implementation of acpi_parse_entries_array() assumes that each
>>> > subtable has a standard ACPI subtable entry of type struct
>>> > acpi_subtable_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.
>>>
>>> Hmm, NFIT has a 2 byte type and a 2 byte length, so its one more
>>> permutation. I happened to reinvent sub-table parsing in the NFIT
>>> driver, but it might be nice in the future to refactor that to use the
>>> common parsing.
>>>
>>> >
>>> > 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@xxxxxxxxxxxxxxx>
>>> > ---
>>> >  drivers/acpi/tables.c | 52 ++++++++++++++++++++++++++++++++++++++++-----------
>>> >  1 file changed, 41 insertions(+), 11 deletions(-)
>>> >
>>> > diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
>>> > index 80ce2a7d224b..f777b94c234a 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) == 0)
>>> > +               return ((struct acpi_hmat_structure *)entry)->type;
>>> > +       else
>>> > +               return ((struct acpi_subtable_header *)entry)->type;
>>> > +}
>>>
>>> It seems inefficient to make all checks keep asking "is HMAT?".
>>
>> Well, ideally, the signature should be checked once.  I guess that can be
>> arranged for here.
>>
>>> Especially if we want to extend this to other table types should we
>>> instead setup and pass a pair of function pointers to parse the
>>> sub-table format?
>>
>> Function pointers may be too much even. :-)
>
> True, how about an enum of acpi sub-table header types?

That works.