target/mips: Fix cycle counter timing calculations

The cp0_count_ns value is calculated from the CP0_COUNT_RATE_DEFAULT
constant in target/mips/cpu.c.  The cycle counter resolution is defined
per-CPU in target/mips/cpu-defs.c.inc; use this value for calculating
cp0_count_ns.  Fixings timing problems on guest OSs for the 20Kc CPU
which has a CCRes of 1.

Signed-off-by: Simon Burge <simonb@NetBSD.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20211213135125.18378-1-simonb@NetBSD.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

diff --git a/target/mips/cpu.c b/target/mips/cpu.c
index 4aae239..0766e25 100644 (file)
--- a/target/mips/cpu.c
+++ b/target/mips/cpu.c
@@ -440,8 +440,9 @@ static void mips_cp0_period_set(MIPSCPU *cpu)
 {
     CPUMIPSState *env = &cpu->env;
 
+    /* env->CCRes isn't initialised this early, use env->cpu_model->CCRes. */
     env->cp0_count_ns = clock_ticks_to_ns(MIPS_CPU(cpu)->clock,
-                                          cpu->cp0_count_rate);
+                                          env->cpu_model->CCRes);
     assert(env->cp0_count_ns);
 }