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[Qemu-devel] [PATCH] [PPC] Make cpu_get_real_ticks use mfspr
From: |
Alexander Graf |
Subject: |
[Qemu-devel] [PATCH] [PPC] Make cpu_get_real_ticks use mfspr |
Date: |
Sat, 3 Apr 2010 11:37:26 +0200 |
PowerPC CPUs have had two ways to read the time base for quite some time now.
They provide it using the mfspr instruction or - if a special bit is set in
that opcode - using mftb. For timekeeping we're currently using mftb.
While trying to get Qemu up and running on an e500v2 system, I stumbled over
the CPU not supporting mftbu. It just throws an illegal instruction trap.
So let's read the SPR values instead. All PPC CPUs should support them anyways.
I tested this patch on an e500v2 system where it makes qemu work and on my 970MP
system with 32-bit user space where everything still works with this patch
applied.
Signed-off-by: Alexander Graf <address@hidden>
---
qemu-timer.h | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/qemu-timer.h b/qemu-timer.h
index a7eac98..d2e15f4 100644
--- a/qemu-timer.h
+++ b/qemu-timer.h
@@ -98,9 +98,9 @@ static inline int64_t cpu_get_real_ticks(void)
#else
/* http://ozlabs.org/pipermail/linuxppc-dev/1999-October/003889.html */
unsigned long junk;
- __asm__ __volatile__ ("mftbu %1\n\t"
- "mftb %L0\n\t"
- "mftbu %0\n\t"
+ __asm__ __volatile__ ("mfspr %1,269\n\t" /* mftbu */
+ "mfspr %L0,268\n\t" /* mftb */
+ "mfspr %0,269\n\t" /* mftbu */
"cmpw %0,%1\n\t"
"bne $-16"
: "=r" (retval), "=r" (junk));
--
1.6.0.2
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