Re: [PATCH v5 3/5] ACPI / processor: Introduce map_gic_id() to get apic id from MADT or _MAT method
From: Marc Zyngier
Date: Sat Feb 22 2014 - 07:11:21 EST
On 2014-02-22 10:21, Hanjun Guo wrote:
On 2014-2-21 20:37, Sudeep Holla wrote:
Hi Hanjun,
(Adding MarcZ for his views on GIC)
On 20/02/14 03:59, Hanjun Guo wrote:
Hi Sudeep,
Thanks for your comments, please refer to the replies below. :)
On 2014å02æ19æ 22:33, Sudeep Holla wrote:
Hi Hanjun,
On 18/02/14 16:23, Hanjun Guo wrote:
Get apic id from MADT or _MAT method is not implemented on
arm/arm64,
and ACPI 5.0 introduces GIC Structure for it, so this patch
introduces
map_gic_id() to get apic id followed the ACPI 5.0 spec.
Signed-off-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
---
drivers/acpi/processor_core.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/drivers/acpi/processor_core.c
b/drivers/acpi/processor_core.c
index 4dcf776..d316d9b 100644
--- a/drivers/acpi/processor_core.c
+++ b/drivers/acpi/processor_core.c
@@ -71,6 +71,27 @@ static int map_lsapic_id(struct
acpi_subtable_header *entry,
return 0;
}
+static int map_gic_id(struct acpi_subtable_header *entry,
+ int device_declaration, u32 acpi_id, int *apic_id)
+{
+ struct acpi_madt_generic_interrupt *gic =
+ (struct acpi_madt_generic_interrupt *)entry;
+
+ if (!(gic->flags & ACPI_MADT_ENABLED))
+ return -ENODEV;
+
+ /* In the GIC interrupt model, logical processors are
+ * required to have a Processor Device object in the DSDT,
+ * so we should check device_declaration here
+ */
+ if (device_declaration && (gic->uid == acpi_id)) {
+ *apic_id = gic->gic_id;
I have mentioned this earlier, it's not clear yet to me how does
this work ?
It needs more clarity in the form of comment here at-least as the
ACPIv5.0 is
also not so clear or explicit on how to handle this.
Yes, I noticed your comments and had a reply for that, after a
long consideration for this, I would withdraw my previous comments
before, please refer to the comments below.
Here you are expecting gic->uid = acpi_id which is fine, while
acpi_map_cpuid
matches apic_id with cpu_physical_id(which must be MPIDR in
ARM{32,64}). The
latter imposes restriction that gic->gic_id has to be MPIDR. Does
that mean we
are imposing restriction on GIC ID to be MPIDR ? If so please
document it here
and please explain the reason behind that choice.
On x86 and IA64, APIC/SAPIC ID is the hardware id of the logical
processor, and UID is just a unique ID to identify the processor in
DSDT, it
can be any value, and even can be strings defined in ASL if I
remember
that correctly.
OK, but that's not the case on ARM{32,64}. My main concern here is
if we don't
make this definitions clear enough, the vendors might produce ACPI
tables with
whatever suits them and we may end up supporting them. Since we are
starting
with clean slate, we can avoid getting into such situations. I will
be to be
more elaborate this time.
I agree.
The GIC ID is referred as the local GICâs hardware ID in ACPIv5.0.
IIUC, since GICC is per-cpu entry, it has to GIC CPU interface ID.
Now how does it differ from MPIDR ? e.g. ARM TC2(multi cluster
system)
GIC ID MPIDR Comment
0 0x000 CA15_0
1 0x001 CA15_1
2 0x100 CA7_0
3 0x101 CA7_1
4 0x102 CA7_2
Yes, obvious different. I know GIC ID can matche the bit index of the
associated processor
in the distributor's GICD_ITARGETSR register, and it a clear
statement in GICv1/GICv2, my
question is that is this consistent in GICv3/v4 too? this will have
some impact on the
code implementation.
For GICv3/v4, the only way you can match a CPU with its local
redistributor is by using the CPU MPIDR. The GIC CPU ID is an
implementation choice that may not exist (it doesn't in a distributed
implementation), so anything that relies on a GIC CPU ID is broken for
GICv3.
M.
--
Fast, cheap, reliable. Pick two.
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