Re: [RFC 4/8] x86_64: Parsing for ACPI "SAPIC" table

[Jack Steiner]

On Tue, Mar 25, 2008 at 12:03:32AM -0400, Len Brown wrote:
> IIR the x2apic scheme entails using the legacy entries for the
> first 256 entries, and extended entries for the processors above that, no?
> 
> Here we seem to be assuming all lapic or all sapic entries.
> 
> -Len
> 

Correct. That is the way it is currently coded & that is the way that
our BIOS creates the tables. Depending on the size of the system, all
entries will be either lapic OR all entries will be sapic.

Currently, the BIOS _tries_ to build legacy-compatible tables. It switches
into x2apic mode only if APICIDs are too big for legacy mode.

I found a statement in the x2apic spec that appears to support that behavior:

	sec 2.11.1 Extended xAPIC Init: BIOS Flow
	  ... There should never be a mixture of legacy and new entries.


However, it is certainly possible that this statement is in conflict with a statement
somewhere else.....



> 
> On Monday 24 March 2008, Jack Steiner wrote:
> > 
> > Add kernel support for new ACPI "sapic" tables that contain 16-bit APICIDs.
> > This patch simply adds parsing of an optional SAPIC table if present.
> > Otherwise, the traditional local APIC table is used.
> > 
> > Note: the SAPIC table is not a new ACPI table - it exists on other architectures
> > but is not currently recognized by x86_64.
> > 
> > 
> > 	Signed-off-by: Jack Steiner <steiner@xxxxxxx>
> > 
> > 
> > ---
> >  arch/x86/kernel/acpi/boot.c |   26 ++++++++++++++++++++++++--
> >  1 file changed, 24 insertions(+), 2 deletions(-)
> > 
> > Index: linux/arch/x86/kernel/acpi/boot.c
> > ===================================================================
> > --- linux.orig/arch/x86/kernel/acpi/boot.c	2008-03-21 15:37:05.000000000 -0500
> > +++ linux/arch/x86/kernel/acpi/boot.c	2008-03-21 15:40:46.000000000 -0500
> > @@ -261,6 +261,24 @@ acpi_parse_lapic(struct acpi_subtable_he
> >  }
> >  
> >  static int __init
> > +acpi_parse_sapic(struct acpi_subtable_header *header, const unsigned long end)
> > +{
> > +	struct acpi_madt_local_sapic *processor = NULL;
> > +
> > +	processor = (struct acpi_madt_local_sapic *)header;
> > +
> > +	if (BAD_MADT_ENTRY(processor, end))
> > +		return -EINVAL;
> > +
> > +	acpi_table_print_madt_entry(header);
> > +
> > +	mp_register_lapic((processor->id << 8) | processor->eid,/* APIC ID */
> > +		processor->lapic_flags & ACPI_MADT_ENABLED);	/* Enabled? */
> > +
> > +	return 0;
> > +}
> > +
> > +static int __init
> >  acpi_parse_lapic_addr_ovr(struct acpi_subtable_header * header,
> >  			  const unsigned long end)
> >  {
> > @@ -753,8 +771,12 @@ static int __init acpi_parse_madt_lapic_
> >  
> >  	mp_register_lapic_address(acpi_lapic_addr);
> >  
> > -	count = acpi_table_parse_madt(ACPI_MADT_TYPE_LOCAL_APIC, acpi_parse_lapic,
> > -				      MAX_APICS);
> > +	count = acpi_table_parse_madt(ACPI_MADT_TYPE_LOCAL_SAPIC,
> > +				      acpi_parse_sapic, MAX_APICS);
> > +
> > +	if (!count)
> > +		count = acpi_table_parse_madt(ACPI_MADT_TYPE_LOCAL_APIC,
> > +					      acpi_parse_lapic, MAX_APICS);
> >  	if (!count) {
> >  		printk(KERN_ERR PREFIX "No LAPIC entries present\n");
> >  		/* TBD: Cleanup to allow fallback to MPS */
> > --
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> > 
> 

-- 
Thanks

Jack Steiner (steiner@xxxxxxx)          651-683-5302
Principal Engineer                      SGI - Silicon Graphics, Inc.


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