x86/{cpu,pit}: implement cpu_delay using the timestamp counter

5 files changed, 77 insertions, 10 deletions

diff --git a/arch/x86/machine/boot.c b/arch/x86/machine/boot.c
index b111a3c0..09ed36eb 100644
--- a/arch/x86/machine/boot.c
+++ b/arch/x86/machine/boot.c
@@ -461,6 +461,7 @@ boot_main(void)
     syscnt_setup();
     percpu_bootstrap();
     trap_setup();
+    pit_setup_free_running();
     cpu_setup();
     thread_bootstrap();
     cga_setup();
@@ -476,7 +477,6 @@ boot_main(void)
     boot_save_data();
     biosmem_free_usable();
     pic_setup();
-    pit_setup();
     cpu_mp_probe();
     kernel_main();
 
diff --git a/arch/x86/machine/cpu.c b/arch/x86/machine/cpu.c
index ff860ba0..d62b68f9 100644
--- a/arch/x86/machine/cpu.c
+++ b/arch/x86/machine/cpu.c
@@ -34,10 +34,16 @@
 #include <machine/cpu.h>
 #include <machine/io.h>
 #include <machine/lapic.h>
+#include <machine/pit.h>
 #include <machine/pmap.h>
 #include <machine/trap.h>
 #include <vm/vm_page.h>
 
+/*
+ * Delay used for frequency measurement, in microseconds.
+ */
+#define CPU_FREQ_CAL_DELAY  1000000
+
 #define CPU_TYPE_MASK       0x00003000
 #define CPU_TYPE_SHIFT      12
 #define CPU_FAMILY_MASK     0x00000f00
@@ -141,6 +147,11 @@ struct cpu cpu_desc __percpu;
 unsigned int cpu_nr_active __read_mostly;
 
 /*
+ * Processor frequency, assumed fixed and equal on all processors.
+ */
+static uint64_t cpu_freq __read_mostly;
+
+/*
  * Interrupt descriptor table.
  */
 static struct cpu_gate_desc cpu_idt[CPU_IDT_SIZE] __aligned(8) __read_mostly;
@@ -154,6 +165,24 @@ static struct cpu_gate_desc cpu_idt[CPU_IDT_SIZE] __aligned(8) __read_mostly;
 static unsigned long cpu_double_fault_handler;
 static char cpu_double_fault_stack[STACK_SIZE] __aligned(DATA_ALIGN);
 
+void
+cpu_delay(unsigned long usecs)
+{
+    int64_t total, prev, count, diff;
+
+    assert(usecs != 0);
+
+    total = DIV_CEIL((int64_t)usecs * cpu_freq, 1000000);
+    prev = cpu_get_tsc();
+
+    do {
+        count = cpu_get_tsc();
+        diff = count - prev;
+        prev = count;
+        total -= diff;
+    } while (total > 0);
+}
+
 void * __init
 cpu_get_boot_stack(void)
 {
@@ -508,6 +537,18 @@ cpu_init(struct cpu *cpu)
     cpu->state = CPU_STATE_ON;
 }
 
+static void __init
+cpu_measure_freq(void)
+{
+    uint64_t start, end;
+
+    start = cpu_get_tsc();
+    pit_delay(CPU_FREQ_CAL_DELAY);
+    end = cpu_get_tsc();
+
+    cpu_freq = (end - start) / (1000000 / CPU_FREQ_CAL_DELAY);
+}
+
 void __init
 cpu_setup(void)
 {
@@ -518,6 +559,8 @@ cpu_setup(void)
     cpu->double_fault_stack = cpu_double_fault_stack; /* XXX */
     cpu_init(cpu);
     cpu_nr_active = 1;
+
+    cpu_measure_freq();
 }
 
 static void __init
@@ -566,6 +609,10 @@ cpu_info(const struct cpu *cpu)
         printf("cpu%u: address widths: physical: %hu, virtual: %hu\n",
                cpu->id, cpu->phys_addr_width, cpu->virt_addr_width);
     }
+
+    printf("cpu%u: frequency: %llu.%02llu MHz\n", cpu->id,
+           (unsigned long long)cpu_freq / 1000000,
+           (unsigned long long)cpu_freq % 1000000);
 }
 
 void __init
diff --git a/arch/x86/machine/cpu.h b/arch/x86/machine/cpu.h
index 3bf1ade3..2360ea7d 100644
--- a/arch/x86/machine/cpu.h
+++ b/arch/x86/machine/cpu.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010-2014 Richard Braun.
+ * Copyright (c) 2010-2017 Richard Braun.
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -479,6 +479,15 @@ cpu_set_msr(uint32_t msr, uint32_t high, uint32_t low)
     asm volatile("wrmsr" : : "c" (msr), "a" (low), "d" (high));
 }
 
+static __always_inline uint64_t
+cpu_get_tsc(void)
+{
+    uint32_t high, low;
+
+    asm volatile("rdtsc" : "=a" (low), "=d" (high));
+    return ((uint64_t)high << 32) | low;
+}
+
 /*
  * Flush non-global TLB entries.
  *
@@ -528,13 +537,9 @@ cpu_tlb_flush_va(unsigned long va)
 }
 
 /*
- * XXX For now, directly use the PIT.
+ * Busy-wait for a given amount of time, in microseconds.
  */
-static inline void
-cpu_delay(unsigned long usecs)
-{
-    pit_delay(usecs);
-}
+void cpu_delay(unsigned long usecs);
 
 /*
  * Return the address of the boot stack allocated for the current processor.
diff --git a/arch/x86/machine/pit.c b/arch/x86/machine/pit.c
index d3fece51..bf53ee11 100644
--- a/arch/x86/machine/pit.c
+++ b/arch/x86/machine/pit.c
@@ -45,7 +45,7 @@
 #define PIT_MAX_COUNT 0xffff
 
 void __init
-pit_setup(void)
+pit_setup_free_running(void)
 {
     io_write_byte(PIT_PORT_MODE, PIT_MODE_RATE_GEN | PIT_MODE_RW_LSB
                                  | PIT_MODE_RW_MSB);
@@ -53,6 +53,12 @@ pit_setup(void)
     io_write_byte(PIT_PORT_COUNTER0, PIT_MAX_COUNT >> 8);
 }
 
+void __init
+pit_setup(void)
+{
+    /* TODO Implement */
+}
+
 static unsigned int
 pit_read(void)
 {
diff --git a/arch/x86/machine/pit.h b/arch/x86/machine/pit.h
index 3b4da60b..7bf7a7b7 100644
--- a/arch/x86/machine/pit.h
+++ b/arch/x86/machine/pit.h
@@ -19,7 +19,16 @@
 #define _X86_PIT_H
 
 /*
- * Set up the i8253 Programmable Interval Timer.
+ * Initialize the PIT as a free running counter.
+ *
+ * This is used during early initialization to measure the frequency of
+ * other clocks. The PIT is used despite its lack of precision because
+ * it's the only architectural timer with a known frequency.
+ */
+void pit_setup_free_running(void);
+
+/*
+ * Initialize the pit module.
  */
 void pit_setup(void);