Patchwork [PPC] Make cpu_get_real_ticks use mfspr

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Submitter Alexander Graf
Date April 3, 2010, 9:37 a.m.
Message ID <1270287446-3904-1-git-send-email-agraf@suse.de>
Download mbox | patch
Permalink /patch/49332/
State New
Headers show

Comments

Alexander Graf - April 3, 2010, 9:37 a.m.
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 <agraf@suse.de>
---
 qemu-timer.h |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

Patch

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));