target/mips/cpu: Make cp0_count_rate a property

Since not all CPU implementations use a cores use a CP0 timer
at half the frequency of the CPU, make this variable a property.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20201012095804.3335117-11-f4bug@amsat.org>

2 files changed, 20 insertions, 8 deletions

diff --git a/target/mips/cpu.c b/target/mips/cpu.c
index 4618813..461edfe 100644
--- a/target/mips/cpu.c
+++ b/target/mips/cpu.c
@@ -26,7 +26,7 @@
 #include "qemu/module.h"
 #include "sysemu/kvm.h"
 #include "exec/exec-all.h"
-
+#include "hw/qdev-properties.h"
 
 static void mips_cpu_set_pc(CPUState *cs, vaddr value)
 {
@@ -135,12 +135,7 @@ static void mips_cpu_disas_set_info(CPUState *s, disassemble_info *info)
 }
 
 /*
- * Since commit 6af0bf9c7c3 this model assumes a CPU clocked at 200MHz
- * and a CP0 timer running at half the clock of the CPU (cp0_count_rate = 2).
- *
- * TIMER_FREQ_HZ = CPU_FREQ_HZ / CP0_COUNT_RATE = 200 MHz / 2 = 100 MHz
- *
- * TIMER_PERIOD_NS = 1 / TIMER_FREQ_HZ = 10 ns
+ * Since commit 6af0bf9c7c3 this model assumes a CPU clocked at 200MHz.
  */
 #define CPU_FREQ_HZ_DEFAULT     200000000
 #define CP0_COUNT_RATE_DEFAULT  2
@@ -149,7 +144,7 @@ static void mips_cp0_period_set(MIPSCPU *cpu)
 {
     CPUMIPSState *env = &cpu->env;
 
-    env->cp0_count_ns = muldiv64(NANOSECONDS_PER_SECOND, CP0_COUNT_RATE_DEFAULT,
+    env->cp0_count_ns = muldiv64(NANOSECONDS_PER_SECOND, cpu->cp0_count_rate,
                                  CPU_FREQ_HZ_DEFAULT);
 }
 
@@ -202,6 +197,13 @@ static ObjectClass *mips_cpu_class_by_name(const char *cpu_model)
     return oc;
 }
 
+static Property mips_cpu_properties[] = {
+    /* CP0 timer running at half the clock of the CPU */
+    DEFINE_PROP_UINT32("cp0-count-rate", MIPSCPU, cp0_count_rate,
+                       CP0_COUNT_RATE_DEFAULT),
+    DEFINE_PROP_END_OF_LIST()
+};
+
 static void mips_cpu_class_init(ObjectClass *c, void *data)
 {
     MIPSCPUClass *mcc = MIPS_CPU_CLASS(c);
@@ -211,6 +213,7 @@ static void mips_cpu_class_init(ObjectClass *c, void *data)
     device_class_set_parent_realize(dc, mips_cpu_realizefn,
                                     &mcc->parent_realize);
     device_class_set_parent_reset(dc, mips_cpu_reset, &mcc->parent_reset);
+    device_class_set_props(dc, mips_cpu_properties);
 
     cc->class_by_name = mips_cpu_class_by_name;
     cc->has_work = mips_cpu_has_work;
diff --git a/target/mips/cpu.h b/target/mips/cpu.h
index 085a88e..baeceb8 100644
--- a/target/mips/cpu.h
+++ b/target/mips/cpu.h
@@ -1151,6 +1151,7 @@ struct CPUMIPSState {
 /**
  * MIPSCPU:
  * @env: #CPUMIPSState
+ * @cp0_count_rate: rate at which the coprocessor 0 counter increments
  *
  * A MIPS CPU.
  */
@@ -1161,6 +1162,14 @@ struct MIPSCPU {
 
     CPUNegativeOffsetState neg;
     CPUMIPSState env;
+    /*
+     * The Count register acts as a timer, incrementing at a constant rate,
+     * whether or not an instruction is executed, retired, or any forward
+     * progress is made through the pipeline. The rate at which the counter
+     * increments is implementation dependent, and is a function of the
+     * pipeline clock of the processor, not the issue width of the processor.
+     */
+    unsigned cp0_count_rate;
 };