Merge remote-tracking branch 'remotes/philmd-gitlab/tags/mips-20210104' into staging

MIPS patches queue

- Use PCI macros (Philippe Mathieu-Daudé)
- Clean up VT82C686B south bridge (BALATON Zoltan)
- Introduce clock_ticks_to_ns() (Peter Maydell)
- Add Loongson-3 machine (Huacai Chen)
- Make addresses used by bootloader unsigned (Jiaxun Yang)
- Clean fuloong2e PROM environment (Jiaxun Yang)
- Add integration test of fuloong2e booting Linux (Jiaxun Yang)

# gpg: Signature made Mon 04 Jan 2021 22:37:48 GMT
# gpg:                using RSA key FAABE75E12917221DCFD6BB2E3E32C2CDEADC0DE
# gpg: Good signature from "Philippe Mathieu-Daudé (F4BUG) <f4bug@amsat.org>" [full]
# Primary key fingerprint: FAAB E75E 1291 7221 DCFD  6BB2 E3E3 2C2C DEAD C0DE

* remotes/philmd-gitlab/tags/mips-20210104: (35 commits)
  tests/acceptance: Test boot_linux_console for fuloong2e
  hw/mips/fuloong2e: Correct cpuclock in PROM environment
  hw/mips/fuloong2e: Remove unused env entry
  hw/mips/fuloong2e: Replace faulty documentation links
  hw/mips/fuloong2e: Remove define DEBUG_FULOONG2E_INIT
  hw/mips: Use address translation helper to handle ENVP_ADDR
  hw/mips/malta: Use address translation helper to calculate bootloader_run_addr
  hw/mips: Make bootloader addresses unsigned
  docs/system: Update MIPS machine documentation
  hw/mips: Add Loongson-3 machine support
  hw/mips: Add Loongson-3 boot parameter helpers
  hw/mips: Implement fw_cfg_arch_key_name()
  hw/intc: Rework Loongson LIOINTC
  clock: Define and use new clock_display_freq()
  clock: Remove clock_get_ns()
  target/mips: Don't use clock_get_ns() in clock period calculation
  clock: Introduce clock_ticks_to_ns()
  vt82c686: Rename superio config related parts
  vt82c686: Use shorter name for local variable holding object state
  vt82c686: Remove unneeded includes and defines
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

2 files changed, 57 insertions, 4 deletions

diff --git a/docs/devel/clocks.rst b/docs/devel/clocks.rst
index e5da28e211..2548d84232 100644
--- a/docs/devel/clocks.rst
+++ b/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:
@@ -254,10 +263,44 @@ 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));
     }
 
+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
+----------------------------
+
+A commonly required operation for a clock is to calculate how long
+it will take for the clock to tick N times; this can then be used
+to set a timer expiry deadline. Use the function ``clock_ticks_to_ns()``,
+which takes an unsigned 64-bit count of ticks and returns the length
+of time in nanoseconds required for the clock to tick that many times.
+
+It is important not to try to calculate expiry deadlines using a
+shortcut like multiplying a "period of clock in nanoseconds" value
+by the tick count, because clocks can have periods which are not a
+whole number of nanoseconds, and the accumulated error in the
+multiplication can be significant.
+
+For a clock with a very long period and a large number of ticks,
+the result of this function could in theory be too large to fit in
+a 64-bit value. To avoid overflow in this case, ``clock_ticks_to_ns()``
+saturates the result to INT64_MAX (because this is the largest valid
+input to the QEMUTimer APIs). Since INT64_MAX nanoseconds is almost
+300 years, anything with an expiry later than that is in the "will
+never happen" category. Callers of ``clock_ticks_to_ns()`` should
+therefore generally not special-case the possibility of a saturated
+result but just allow the timer to be set to that far-future value.
+(If you are performing further calculations on the returned value
+rather than simply passing it to a QEMUTimer function like
+``timer_mod_ns()`` then you should be careful to avoid overflow
+in those calculations, of course.)
+
 Changing a clock period
 -----------------------
 
diff --git a/docs/system/target-mips.rst b/docs/system/target-mips.rst
index cd2a931edf..138441bdec 100644
--- a/docs/system/target-mips.rst
+++ b/docs/system/target-mips.rst
@@ -84,6 +84,16 @@ The Fuloong 2E emulation supports:
 
 -  RTL8139D as a network card chipset
 
+The Loongson-3 virtual platform emulation supports:
+
+-  Loongson 3A CPU
+
+-  LIOINTC as interrupt controller
+
+-  GPEX and virtio as peripheral devices
+
+-  Both KVM and TCG supported
+
 The mipssim pseudo board emulation provides an environment similar to
 what the proprietary MIPS emulator uses for running Linux. It supports: