x86: Move some fixed or dummy config information into X86LocalApic.py.

The X86 local APIC doesn't actually use the pio_addr set in the config
and instead computes what address it will respond to based on the
initial ID of the CPU it's attached to. gem5's BasicPioDevice, which
the X86LocalApic class inherits from, does not provide a default value
for that parameter and will complain if *something* isn't set. The
value used, 0x2000000000000000, is a dummy value which is the base of
the region of the physical address space set aside for messages to
local APICs from the CPU and from other local APICs.

Also, the clock for the local APIC's timer is defined to be the bus
clock. The assumption seems to be that this has a 16:1 ratio with the
CPU clock, and I vaguely remember finding that that was more or less
unofficially true, even if it isn't necessary stringently defined to
be that.

Since we were already just assuming that that ratio was correct and
always setting up the local APICs clock that way, we can do that in
the X86LocalApic class definition and remove some special x86 specific
setup that we'd otherwise need for the x86 version of the Interrupt
class. If that's not correct, it can still be overridden somewhere else
in the config.

Change-Id: I50e84f899f44b1191c2ad79d05803b44f07001f9
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/19968
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/arch/x86/X86LocalApic.py b/src/arch/x86/X86LocalApic.py
index 5d4910e98..c1b835ccb 100644
--- a/src/arch/x86/X86LocalApic.py
+++ b/src/arch/x86/X86LocalApic.py
@@ -43,6 +43,7 @@ from m5.params import *
 from m5.proxy import *
 
 from m5.objects.Device import BasicPioDevice
+from m5.objects.ClockDomain import DerivedClockDomain
 
 class X86LocalApic(BasicPioDevice):
     type = 'X86LocalApic'
@@ -52,3 +53,15 @@ class X86LocalApic(BasicPioDevice):
     int_slave = SlavePort("Port for receiving interrupt messages")
     int_latency = Param.Latency('1ns', \
             "Latency for an interrupt to propagate through this device.")
+
+    # pio_addr isn't used by the local APIC model since it's address is
+    # calculated dynamically using the initial ID of the CPU it's attached to,
+    # but it needs to be set to something to make the BasicPioDevice happy.
+    pio_addr = 0x2000000000000000
+
+    # The clock rate for the local APIC timer is supposed to be the "bus clock"
+    # which we assume is 1/16th the rate of the CPU clock. I don't think this
+    # is a hard rule, but seems to be true in practice. This can be overriden
+    # in configs that use it.
+    clk_domain = DerivedClockDomain(
+            clk_domain=Parent.clk_domain, clk_divider=16)