clock: Remove clock_get_ns()

Remove the now-unused clock_get_ns() API and the CLOCK_PERIOD_TO_NS()
macro that only it was using.

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: <20201215150929.30311-4-peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

docs/devel/clocks.rst

@@ -238,8 +238,17 @@ object during device instance init. For example:
 Fetching clock frequency/period
 -------------------------------
 
-To get the current state of a clock, use the functions ``clock_get()``,
-``clock_get_ns()`` or ``clock_get_hz()``.
+To get the current state of a clock, use the functions ``clock_get()``
+or ``clock_get_hz()``.
+
+``clock_get()`` returns the period of the clock in its fully precise
+internal representation, as an unsigned 64-bit integer in units of
+2^-32 nanoseconds. (For many purposes ``clock_ticks_to_ns()`` will
+be more convenient; see the section below on expiry deadlines.)
+
+``clock_get_hz()`` returns the frequency of the clock, rounded to the
+next lowest integer. This implies some inaccuracy due to the rounding,
+so be cautious about using it in calculations.
 
 It is also possible to register a callback on clock frequency changes.
 Here is an example:
@@ -254,8 +263,8 @@ Here is an example:
          */
 
         /* do something with the new period */
-        fprintf(stdout, "device new period is %" PRIu64 "ns\n",
-                        clock_get_ns(dev->my_clk_input));
+        fprintf(stdout, "device new period is %" PRIu64 "* 2^-32 ns\n",
+                        clock_get(dev->my_clk_input));
     }
 
 Calculating expiry deadlines

include/hw/clock.h

@@ -40,7 +40,6 @@ typedef void ClockCallback(void *opaque);
  * macro helpers to convert to hertz / nanosecond
  */
 #define CLOCK_PERIOD_FROM_NS(ns) ((ns) * (CLOCK_PERIOD_1SEC / 1000000000llu))
-#define CLOCK_PERIOD_TO_NS(per) ((per) / (CLOCK_PERIOD_1SEC / 1000000000llu))
 #define CLOCK_PERIOD_FROM_HZ(hz) (((hz) != 0) ? CLOCK_PERIOD_1SEC / (hz) : 0u)
 #define CLOCK_PERIOD_TO_HZ(per) (((per) != 0) ? CLOCK_PERIOD_1SEC / (per) : 0u)
 
@@ -215,11 +214,6 @@ static inline unsigned clock_get_hz(Clock *clk)
     return CLOCK_PERIOD_TO_HZ(clock_get(clk));
 }
 
-static inline unsigned clock_get_ns(Clock *clk)
-{
-    return CLOCK_PERIOD_TO_NS(clock_get(clk));
-}
-
 /**
  * clock_ticks_to_ns:
  * @clk: the clock to query