[Qemu-ppc] [PATCH v2] PPC: Introduce the Virtual Time Base (VTB) SPR register

[Cyril Bur]

This patch adds basic support for the VTB.

PowerISA:
The Virtual Time Base (VTB) is a 64-bit incrementing counter.
Virtual Time Base increments at the same rate as the Time Base until its value
becomes 0xFFFF_FFFF_FFFF_FFFF (2 64 - 1); at the next increment its value
becomes 0x0000_0000_0000_0000. There is no interrupt or other indication when
this occurs.

The operation of the Virtual Time Base has the following additional
properties.
1. Loading a GPR from the Virtual Time Base has no effect on the accuracy of
the Virtual Time Base.
2. Copying the contents of a GPR to the Virtual Time Base replaces the
contents of the Virtual Time Base with the contents of the GPR.

Signed-off-by: Cyril Bur <address@hidden>
---
V2:
   Drop the use of spr_read_vtb() and just use spr_read_tbl() as a handler for 
VTB
reads
   Correct the permissions for user mode access of the VTB

---
 target-ppc/cpu.h            |  1 +
 target-ppc/translate_init.c | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/target-ppc/cpu.h b/target-ppc/cpu.h
index b706b9f..abc3545 100644
--- a/target-ppc/cpu.h
+++ b/target-ppc/cpu.h
@@ -1624,6 +1624,7 @@ static inline int cpu_mmu_index (CPUPPCState *env)
 #define SPR_MPC_MD_DBRAM1     (0x32A)
 #define SPR_RCPU_L2U_RA3      (0x32B)
 #define SPR_TAR               (0x32F)
+#define SPR_VTB               (0x351)
 #define SPR_440_INV0          (0x370)
 #define SPR_440_INV1          (0x371)
 #define SPR_440_INV2          (0x372)
diff --git a/target-ppc/translate_init.c b/target-ppc/translate_init.c
index df1a62c..201761e 100644
--- a/target-ppc/translate_init.c
+++ b/target-ppc/translate_init.c
@@ -873,6 +873,15 @@ static void gen_tbl (CPUPPCState *env)
                  0x00000000);
 }
 
+/* Virtual Time Base */
+static void gen_spr_vtb(CPUPPCState *env)
+{
+    spr_register(env, SPR_VTB, "VTB",
+                 SPR_NOACCESS, SPR_NOACCESS,
+                 &spr_read_tbl, SPR_NOACCESS,
+                 0x00000000);
+}
+
 /* Softare table search registers */
 static void gen_6xx_7xx_soft_tlb (CPUPPCState *env, int nb_tlbs, int nb_ways)
 {
@@ -7881,6 +7890,7 @@ static void init_proc_book3s_64(CPUPPCState *env, int 
version)
         gen_spr_power8_pmu_sup(env);
         gen_spr_power8_pmu_user(env);
         gen_spr_power8_tm(env);
+        gen_spr_vtb(env);
     }
     if (version < BOOK3S_CPU_POWER8) {
         gen_spr_book3s_dbg(env);
-- 
1.9.1