target/mips: Rework cp0_timer with clock API

Previous implementation of MIPS cp0_timer computes a
cp0_count_ns based on input clock. However rounding
error of cp0_count_ns can affect precision of cp0_timer.

Using clock API and a divider for cp0_timer, so we can
use clock_ns_to_ticks/clock_ns_to_ticks to avoid rounding
issue.

Also workaround the situation that in such handler flow:

count = read_c0_count()
write_c0_compare(count)

If timer had not progressed when compare was written, the
interrupt would trigger again.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230521110037.90049-1-jiaxun.yang@flygoat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/target/mips/cpu.c b/target/mips/cpu.c
index 01e0fbe..b7119cb 100644
--- a/target/mips/cpu.c
+++ b/target/mips/cpu.c
@@ -449,9 +449,9 @@ static void mips_cp0_period_set(MIPSCPU *cpu)
 {
     CPUMIPSState *env = &cpu->env;
 
-    env->cp0_count_ns = clock_ticks_to_ns(MIPS_CPU(cpu)->clock,
-                                          env->cpu_model->CCRes);
-    assert(env->cp0_count_ns);
+    clock_set_mul_div(cpu->count_div, env->cpu_model->CCRes, 1);
+    clock_set_source(cpu->count_div, cpu->clock);
+    clock_set_source(env->count_clock, cpu->count_div);
 }
 
 static void mips_cpu_realizefn(DeviceState *dev, Error **errp)
@@ -504,6 +504,8 @@ static void mips_cpu_initfn(Object *obj)
 
     cpu_set_cpustate_pointers(cpu);
     cpu->clock = qdev_init_clock_in(DEVICE(obj), "clk-in", NULL, cpu, 0);
+    cpu->count_div = clock_new(OBJECT(obj), "clk-div-count");
+    env->count_clock = clock_new(OBJECT(obj), "clk-count");
     env->cpu_model = mcc->cpu_def;
 }