clock: Define and use new clock_display_freq()

It's common to want to print a human-readable indication of a clock's
frequency. Provide a utility function in the clock API to return a
string which is a displayable representation of the frequency,
and use it in qdev-monitor.c.

Before:

  (qemu) info qtree
  [...]
  dev: xilinx,zynq_slcr, id ""
    clock-in "ps_clk" freq_hz=3.333333e+07
    mmio 00000000f8000000/0000000000001000

After:

  dev: xilinx,zynq_slcr, id ""
    clock-in "ps_clk" freq_hz=33.3 MHz
    mmio 00000000f8000000/0000000000001000

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Luc Michel <luc@lmichel.fr>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20201215150929.30311-5-peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

docs/devel/clocks.rst

@@ -267,6 +267,11 @@ Here is an example:
                         clock_get(dev->my_clk_input));
     }
 
+If you are only interested in the frequency for displaying it to
+humans (for instance in debugging), use ``clock_display_freq()``,
+which returns a prettified string-representation, e.g. "33.3 MHz".
+The caller must free the string with g_free() after use.
+
 Calculating expiry deadlines
 ----------------------------
 

hw/core/clock.c

@@ -12,6 +12,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/cutils.h"
 #include "hw/clock.h"
 #include "trace.h"
 
@@ -111,6 +112,11 @@ static void clock_disconnect(Clock *clk)
     QLIST_REMOVE(clk, sibling);
 }
 
+char *clock_display_freq(Clock *clk)
+{
+    return freq_to_str(clock_get_hz(clk));
+}
+
 static void clock_initfn(Object *obj)
 {
     Clock *clk = CLOCK(obj);

include/hw/clock.h

@@ -264,4 +264,16 @@ static inline bool clock_is_enabled(const Clock *clk)
     return clock_get(clk) != 0;
 }
 
+/**
+ * clock_display_freq: return human-readable representation of clock frequency
+ * @clk: clock
+ *
+ * Return a string which has a human-readable representation of the
+ * clock's frequency, e.g. "33.3 MHz". This is intended for debug
+ * and display purposes.
+ *
+ * The caller is responsible for freeing the string with g_free().
+ */
+char *clock_display_freq(Clock *clk);
+
 #endif /* QEMU_HW_CLOCK_H */

softmmu/qdev-monitor.c

@@ -736,11 +736,11 @@ static void qdev_print(Monitor *mon, DeviceState *dev, int indent)
         }
     }
     QLIST_FOREACH(ncl, &dev->clocks, node) {
-        qdev_printf("clock-%s%s \"%s\" freq_hz=%e\n",
+        g_autofree char *freq_str = clock_display_freq(ncl->clock);
+        qdev_printf("clock-%s%s \"%s\" freq_hz=%s\n",
                     ncl->output ? "out" : "in",
                     ncl->alias ? " (alias)" : "",
-                    ncl->name,
-                    CLOCK_PERIOD_TO_HZ(1.0 * clock_get(ncl->clock)));
+                    ncl->name, freq_str);
     }
     class = object_get_class(OBJECT(dev));
     do {