Merge remote-tracking branch 'remotes/pmaydell/tags/pull-target-arm-20210129-1' into staging

target-arm queue:
 * Implement ID_PFR2
 * Conditionalize DBGDIDR
 * rename xlnx-zcu102.canbusN properties
 * provide powerdown/reset mechanism for secure firmware on 'virt' board
 * hw/misc: Fix arith overflow in NPCM7XX PWM module
 * target/arm: Replace magic value by MMU_DATA_LOAD definition
 * configure: fix preadv errors on Catalina macOS with new XCode
 * Various configure and other cleanups in preparation for iOS support
 * hvf: Add hypervisor entitlement to output binaries (needed for Big Sur)
 * Implement pvpanic-pci device
 * Convert the CMSDK timer devices to the Clock framework

# gpg: Signature made Fri 29 Jan 2021 16:08:02 GMT
# gpg:                using RSA key E1A5C593CD419DE28E8315CF3C2525ED14360CDE
# gpg:                issuer "peter.maydell@linaro.org"
# gpg: Good signature from "Peter Maydell <peter.maydell@linaro.org>" [ultimate]
# gpg:                 aka "Peter Maydell <pmaydell@gmail.com>" [ultimate]
# gpg:                 aka "Peter Maydell <pmaydell@chiark.greenend.org.uk>" [ultimate]
# Primary key fingerprint: E1A5 C593 CD41 9DE2 8E83  15CF 3C25 25ED 1436 0CDE

* remotes/pmaydell/tags/pull-target-arm-20210129-1: (46 commits)
  hw/arm/stellaris: Remove board-creation reset of STELLARIS_SYS
  arm: Remove frq properties on CMSDK timer, dualtimer, watchdog, ARMSSE
  arm: Don't set freq properties on CMSDK timer, dualtimer, watchdog, ARMSSE
  hw/arm/armsse: Use Clock to set system_clock_scale
  tests/qtest/cmsdk-apb-watchdog-test: Test clock changes
  hw/watchdog/cmsdk-apb-watchdog: Convert to use Clock input
  hw/timer/cmsdk-apb-dualtimer: Convert to use Clock input
  hw/timer/cmsdk-apb-timer: Convert to use Clock input
  hw/arm/stellaris: Create Clock input for watchdog
  hw/arm/stellaris: Convert SSYS to QOM device
  hw/arm/musca: Create and connect ARMSSE Clocks
  hw/arm/mps2-tz: Create and connect ARMSSE Clocks
  hw/arm/mps2: Create and connect SYSCLK Clock
  hw/arm/mps2: Inline CMSDK_APB_TIMER creation
  hw/arm/armsse: Wire up clocks
  hw/arm/armsse: Rename "MAINCLK" property to "MAINCLK_FRQ"
  hw/watchdog/cmsdk-apb-watchdog: Add Clock input
  hw/timer/cmsdk-apb-dualtimer: Add Clock input
  hw/timer/cmsdk-apb-timer: Add Clock input
  hw/timer/cmsdk-apb-timer: Rename CMSDKAPBTIMER struct to CMSDKAPBTimer
  ...

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

1 files changed, 16 insertions, 0 deletions

diff --git a/docs/devel/clocks.rst b/docs/devel/clocks.rst
index 2548d84232..c54bbb8240 100644
--- a/docs/devel/clocks.rst
+++ b/docs/devel/clocks.rst
@@ -235,6 +235,22 @@ object during device instance init. For example:
     /* set initial value to 10ns / 100MHz */
     clock_set_ns(clk, 10);
 
+To enforce that the clock is wired up by the board code, you can
+call ``clock_has_source()`` in your device's realize method:
+
+.. code-block:: c
+
+   if (!clock_has_source(s->clk)) {
+       error_setg(errp, "MyDevice: clk input must be connected");
+       return;
+   }
+
+Note that this only checks that the clock has been wired up; it is
+still possible that the output clock connected to it is disabled
+or has not yet been configured, in which case the period will be
+zero. You should use the clock callback to find out when the clock
+period changes.
+
 Fetching clock frequency/period
 -------------------------------