[PATCH 1/2] x86, ioapic: Reserve only 128 bytes for IOAPICs

[Bjorn Helgaas]

Previously we reserved 1024 bytes, but that's more space than the IOAPIC
consumes, and it can cause conflicts with nearby devices.  The known
requirement is 68 bytes (sizeof(struct io_apic)), and rounding up to a
power-of-2 gives us 128.

The bug reported below is caused by the following assignments (the IOAPIC
power-on default and the watchdog address recommended in the AMD SP5100
BIOS Developer's Guide):

  IOAPIC[0]        at [mem 0xfec00000-0xfec003ff]
  SP5100 TCO timer at [mem 0xfec000f0-0xfec000f7]

Reported-by: Ralf Jung ralfjung-e@xxxxxx
Reference: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=638863
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
---
 arch/x86/include/asm/apicdef.h |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/apicdef.h b/arch/x86/include/asm/apicdef.h
index 34595d5..855a18a 100644
--- a/arch/x86/include/asm/apicdef.h
+++ b/arch/x86/include/asm/apicdef.h
@@ -12,10 +12,11 @@
 #define	APIC_DEFAULT_PHYS_BASE		0xfee00000
 
 /*
- * This is the IO-APIC register space as specified
- * by Intel docs:
+ * I/O APICs are accessed indirectly via an index/data pair and an EOI
+ * register.  For example, see sec 13.5.1, "APIC Register Map," in the
+ * Intel ICH10 datasheet and the struct io_apic definition.
  */
-#define IO_APIC_SLOT_SIZE		1024
+#define IO_APIC_SLOT_SIZE		128
 
 #define	APIC_ID		0x20
 

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