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From: Peter Maydell <peter.maydell@linaro.org>
To: qemu-devel@nongnu.org
Subject: [PULL 35/51] clock: Provide builtin multiplier/divider
Date: Wed,  1 Sep 2021 11:36:37 +0100	[thread overview]
Message-ID: <20210901103653.13435-36-peter.maydell@linaro.org> (raw)
In-Reply-To: <20210901103653.13435-1-peter.maydell@linaro.org>

It is quite common for a clock tree to involve possibly programmable
clock multipliers or dividers, where the frequency of a clock is for
instance divided by 8 to produce a slower clock to feed to a
particular device.

Currently we provide no convenient mechanism for modelling this.  You
can implement it by having an input Clock and an output Clock, and
manually setting the period of the output clock in the period-changed
callback of the input clock, but that's quite clunky.

This patch adds support in the Clock objects themselves for setting a
multiplier or divider.  The effect of setting this on a clock is that
when the clock's period is changed, all the children of the clock are
set to period * multiplier / divider, rather than being set to the
same period as the parent clock.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alexandre Iooss <erdnaxe@crans.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Luc Michel <luc@lmichel.fr>
Reviewed-by: Damien Hedde <damien.hedde@greensocs.com>
Message-id: 20210812093356.1946-10-peter.maydell@linaro.org
---
 docs/devel/clocks.rst   | 23 +++++++++++++++++++++++
 include/hw/clock.h      | 29 +++++++++++++++++++++++++++++
 hw/core/clock-vmstate.c | 40 +++++++++++++++++++++++++++++++++++++++-
 hw/core/clock.c         | 31 +++++++++++++++++++++++++++----
 hw/core/trace-events    |  1 +
 5 files changed, 119 insertions(+), 5 deletions(-)

diff --git a/docs/devel/clocks.rst b/docs/devel/clocks.rst
index 956bd147ea0..675fbeb6abe 100644
--- a/docs/devel/clocks.rst
+++ b/docs/devel/clocks.rst
@@ -260,6 +260,29 @@ clocks get the new clock period value: *Clock 2*, *Clock 3* and *Clock 4*.
 It is not possible to disconnect a clock or to change the clock connection
 after it is connected.
 
+Clock multiplier and divider settings
+-------------------------------------
+
+By default, when clocks are connected together, the child
+clocks run with the same period as their source (parent) clock.
+The Clock API supports a built-in period multiplier/divider
+mechanism so you can configure a clock to make its children
+run at a different period from its own. If you call the
+``clock_set_mul_div()`` function you can specify the clock's
+multiplier and divider values. The children of that clock
+will all run with a period of ``parent_period * multiplier / divider``.
+For instance, if the clock has a frequency of 8MHz and you set its
+multiplier to 2 and its divider to 3, the child clocks will run
+at 12MHz.
+
+You can change the multiplier and divider of a clock at runtime,
+so you can use this to model clock controller devices which
+have guest-programmable frequency multipliers or dividers.
+
+Note that ``clock_set_mul_div()`` does not automatically call
+``clock_propagate()``. If you make a runtime change to the
+multiplier or divider you must call clock_propagate() yourself.
+
 Unconnected input clocks
 ------------------------
 
diff --git a/include/hw/clock.h b/include/hw/clock.h
index a7187eab95e..11f67fb9701 100644
--- a/include/hw/clock.h
+++ b/include/hw/clock.h
@@ -81,6 +81,10 @@ struct Clock {
     void *callback_opaque;
     unsigned int callback_events;
 
+    /* Ratio of the parent clock to run the child clocks at */
+    uint32_t multiplier;
+    uint32_t divider;
+
     /* Clocks are organized in a clock tree */
     Clock *source;
     QLIST_HEAD(, Clock) children;
@@ -350,4 +354,29 @@ static inline bool clock_is_enabled(const Clock *clk)
  */
 char *clock_display_freq(Clock *clk);
 
+/**
+ * clock_set_mul_div: set multiplier/divider for child clocks
+ * @clk: clock
+ * @multiplier: multiplier value
+ * @divider: divider value
+ *
+ * By default, a Clock's children will all run with the same period
+ * as their parent. This function allows you to adjust the multiplier
+ * and divider used to derive the child clock frequency.
+ * For example, setting a multiplier of 2 and a divider of 3
+ * will run child clocks with a period 2/3 of the parent clock,
+ * so if the parent clock is an 8MHz clock the children will
+ * be 12MHz.
+ *
+ * Setting the multiplier to 0 will stop the child clocks.
+ * Setting the divider to 0 is a programming error (diagnosed with
+ * an assertion failure).
+ * Setting a multiplier value that results in the child period
+ * overflowing is not diagnosed.
+ *
+ * Note that this function does not call clock_propagate(); the
+ * caller should do that if necessary.
+ */
+void clock_set_mul_div(Clock *clk, uint32_t multiplier, uint32_t divider);
+
 #endif /* QEMU_HW_CLOCK_H */
diff --git a/hw/core/clock-vmstate.c b/hw/core/clock-vmstate.c
index 260b13fc2c8..9d9174ffbd7 100644
--- a/hw/core/clock-vmstate.c
+++ b/hw/core/clock-vmstate.c
@@ -14,12 +14,50 @@
 #include "migration/vmstate.h"
 #include "hw/clock.h"
 
+static bool muldiv_needed(void *opaque)
+{
+    Clock *clk = opaque;
+
+    return clk->multiplier != 1 || clk->divider != 1;
+}
+
+static int clock_pre_load(void *opaque)
+{
+    Clock *clk = opaque;
+    /*
+     * The initial out-of-reset settings of the Clock might have been
+     * configured by the device to be different from what we set
+     * in clock_initfn(), so we must here set the default values to
+     * be used if they are not in the inbound migration state.
+     */
+    clk->multiplier = 1;
+    clk->divider = 1;
+
+    return 0;
+}
+
+const VMStateDescription vmstate_muldiv = {
+    .name = "clock/muldiv",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = muldiv_needed,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(multiplier, Clock),
+        VMSTATE_UINT32(divider, Clock),
+    },
+};
+
 const VMStateDescription vmstate_clock = {
     .name = "clock",
     .version_id = 0,
     .minimum_version_id = 0,
+    .pre_load = clock_pre_load,
     .fields = (VMStateField[]) {
         VMSTATE_UINT64(period, Clock),
         VMSTATE_END_OF_LIST()
-    }
+    },
+    .subsections = (const VMStateDescription*[]) {
+        &vmstate_muldiv,
+        NULL
+    },
 };
diff --git a/hw/core/clock.c b/hw/core/clock.c
index fc5a99683f8..916875e07a2 100644
--- a/hw/core/clock.c
+++ b/hw/core/clock.c
@@ -64,6 +64,15 @@ bool clock_set(Clock *clk, uint64_t period)
     return true;
 }
 
+static uint64_t clock_get_child_period(Clock *clk)
+{
+    /*
+     * Return the period to be used for child clocks, which is the parent
+     * clock period adjusted for for multiplier and divider effects.
+     */
+    return muldiv64(clk->period, clk->multiplier, clk->divider);
+}
+
 static void clock_call_callback(Clock *clk, ClockEvent event)
 {
     /*
@@ -78,15 +87,16 @@ static void clock_call_callback(Clock *clk, ClockEvent event)
 static void clock_propagate_period(Clock *clk, bool call_callbacks)
 {
     Clock *child;
+    uint64_t child_period = clock_get_child_period(clk);
 
     QLIST_FOREACH(child, &clk->children, sibling) {
-        if (child->period != clk->period) {
+        if (child->period != child_period) {
             if (call_callbacks) {
                 clock_call_callback(child, ClockPreUpdate);
             }
-            child->period = clk->period;
+            child->period = child_period;
             trace_clock_update(CLOCK_PATH(child), CLOCK_PATH(clk),
-                               CLOCK_PERIOD_TO_HZ(clk->period),
+                               CLOCK_PERIOD_TO_HZ(child->period),
                                call_callbacks);
             if (call_callbacks) {
                 clock_call_callback(child, ClockUpdate);
@@ -110,7 +120,7 @@ void clock_set_source(Clock *clk, Clock *src)
 
     trace_clock_set_source(CLOCK_PATH(clk), CLOCK_PATH(src));
 
-    clk->period = src->period;
+    clk->period = clock_get_child_period(src);
     QLIST_INSERT_HEAD(&src->children, clk, sibling);
     clk->source = src;
     clock_propagate_period(clk, false);
@@ -133,10 +143,23 @@ char *clock_display_freq(Clock *clk)
     return freq_to_str(clock_get_hz(clk));
 }
 
+void clock_set_mul_div(Clock *clk, uint32_t multiplier, uint32_t divider)
+{
+    assert(divider != 0);
+
+    trace_clock_set_mul_div(CLOCK_PATH(clk), clk->multiplier, multiplier,
+                            clk->divider, divider);
+    clk->multiplier = multiplier;
+    clk->divider = divider;
+}
+
 static void clock_initfn(Object *obj)
 {
     Clock *clk = CLOCK(obj);
 
+    clk->multiplier = 1;
+    clk->divider = 1;
+
     QLIST_INIT(&clk->children);
 }
 
diff --git a/hw/core/trace-events b/hw/core/trace-events
index 360ddeb2c87..9b3ecce3b2f 100644
--- a/hw/core/trace-events
+++ b/hw/core/trace-events
@@ -34,3 +34,4 @@ clock_disconnect(const char *clk) "'%s'"
 clock_set(const char *clk, uint64_t old, uint64_t new) "'%s', %"PRIu64"Hz->%"PRIu64"Hz"
 clock_propagate(const char *clk) "'%s'"
 clock_update(const char *clk, const char *src, uint64_t hz, int cb) "'%s', src='%s', val=%"PRIu64"Hz cb=%d"
+clock_set_mul_div(const char *clk, uint32_t oldmul, uint32_t mul, uint32_t olddiv, uint32_t div) "'%s', mul: %u -> %u, div: %u -> %u"
-- 
2.20.1



  parent reply	other threads:[~2021-09-01 11:06 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-01 10:36 [PULL 00/51] target-arm queue Peter Maydell
2021-09-01 10:36 ` [PULL 01/51] tests: Remove uses of deprecated raspi2/raspi3 machine names Peter Maydell
2021-09-01 10:36 ` [PULL 02/51] hw/arm/raspi: Remove deprecated raspi2/raspi3 aliases Peter Maydell
2021-09-01 10:36 ` [PULL 03/51] hw/intc/arm_gicv3_dist: Rename 64-bit accessors with 'q' suffix Peter Maydell
2021-09-01 10:36 ` [PULL 04/51] hw/intc/arm_gicv3: Replace mis-used MEMTX_* constants by booleans Peter Maydell
2021-09-01 10:36 ` [PULL 05/51] hw: Add compat machines for 6.2 Peter Maydell
2021-09-01 10:36 ` [PULL 06/51] target/arm: Implement MVE VADD (floating-point) Peter Maydell
2021-09-01 10:36 ` [PULL 07/51] target/arm: Implement MVE VSUB, VMUL, VABD, VMAXNM, VMINNM Peter Maydell
2021-09-01 10:36 ` [PULL 08/51] target/arm: Implement MVE VCADD Peter Maydell
2021-09-01 10:36 ` [PULL 09/51] target/arm: Implement MVE VFMA and VFMS Peter Maydell
2021-09-01 10:36 ` [PULL 10/51] target/arm: Implement MVE VCMUL and VCMLA Peter Maydell
2021-09-01 10:36 ` [PULL 11/51] target/arm: Implement MVE VMAXNMA and VMINNMA Peter Maydell
2021-09-01 10:36 ` [PULL 12/51] target/arm: Implement MVE scalar fp insns Peter Maydell
2021-09-01 10:36 ` [PULL 13/51] target/arm: Implement MVE fp-with-scalar VFMA, VFMAS Peter Maydell
2021-09-01 10:36 ` [PULL 14/51] softfloat: Remove assertion preventing silencing of NaN in default-NaN mode Peter Maydell
2021-09-01 10:36 ` [PULL 15/51] target/arm: Implement MVE FP max/min across vector Peter Maydell
2021-09-01 10:36 ` [PULL 16/51] target/arm: Implement MVE fp vector comparisons Peter Maydell
2021-09-01 10:36 ` [PULL 17/51] target/arm: Implement MVE fp scalar comparisons Peter Maydell
2021-09-01 10:36 ` [PULL 18/51] target/arm: Implement MVE VCVT between floating and fixed point Peter Maydell
2021-09-01 10:36 ` [PULL 19/51] target/arm: Implement MVE VCVT between fp and integer Peter Maydell
2021-09-01 10:36 ` [PULL 20/51] target/arm: Implement MVE VCVT with specified rounding mode Peter Maydell
2021-09-01 10:36 ` [PULL 21/51] target/arm: Implement MVE VCVT between single and half precision Peter Maydell
2021-09-01 10:36 ` [PULL 22/51] target/arm: Implement MVE VRINT insns Peter Maydell
2021-09-01 10:36 ` [PULL 23/51] target/arm: Enable MVE in Cortex-M55 Peter Maydell
2021-09-01 10:36 ` [PULL 24/51] target-arm: Add support for Fujitsu A64FX Peter Maydell
2021-09-01 10:36 ` [PULL 25/51] hw/arm/virt: target-arm: Add A64FX processor support to virt machine Peter Maydell
2021-09-01 10:36 ` [PULL 26/51] tests/arm-cpu-features: Add A64FX processor related tests Peter Maydell
2021-09-01 10:36 ` [PULL 27/51] arm: Move M-profile RAS register block into its own device Peter Maydell
2021-09-01 10:36 ` [PULL 28/51] arm: Move systick device creation from NVIC to ARMv7M object Peter Maydell
2021-09-01 10:36 ` [PULL 29/51] arm: Move system PPB container handling to armv7m Peter Maydell
2021-09-01 10:36 ` [PULL 30/51] hw/timer/armv7m_systick: Add usual QEMU interface comment Peter Maydell
2021-09-01 10:36 ` [PULL 31/51] hw/timer/armv7m_systick: Add input clocks Peter Maydell
2021-09-01 10:36 ` [PULL 32/51] hw/arm/armv7m: Create " Peter Maydell
2021-09-01 10:36 ` [PULL 33/51] armsse: Wire up systick cpuclk clock Peter Maydell
2021-09-01 10:36 ` [PULL 34/51] hw/arm/mps2.c: Connect up armv7m clocks Peter Maydell
2021-09-01 10:36 ` Peter Maydell [this message]
2021-09-01 10:36 ` [PULL 36/51] hw/arm: Don't allocate separate MemoryRegions in stm32 SoC realize Peter Maydell
2021-09-01 10:36 ` [PULL 37/51] hw/arm/stm32f100: Wire up sysclk and refclk Peter Maydell
2021-09-01 10:36 ` [PULL 38/51] hw/arm/stm32f205: " Peter Maydell
2021-09-01 10:36 ` [PULL 39/51] hw/arm/stm32f405: " Peter Maydell
2021-09-01 10:36 ` [PULL 40/51] hw/arm/stm32vldiscovery: Delete trailing blank line Peter Maydell
2021-09-01 10:36 ` [PULL 41/51] hw/arm/nrf51: Wire up sysclk Peter Maydell
2021-09-01 10:36 ` [PULL 42/51] hw/arm/stellaris: split stellaris_sys_init() Peter Maydell
2021-09-01 10:36 ` [PULL 43/51] hw/arm/stellaris: Wire sysclk up to armv7m Peter Maydell
2021-09-01 10:36 ` [PULL 44/51] hw/arm/msf2_soc: Don't allocate separate MemoryRegions Peter Maydell
2021-09-01 10:36 ` [PULL 45/51] hw/arm/msf2: Use Clock input to MSF2_SOC instead of m3clk property Peter Maydell
2021-09-01 10:36 ` [PULL 46/51] hw/arm/msf2-soc: Wire up refclk Peter Maydell
2021-09-01 10:36 ` [PULL 47/51] hw/timer/armv7m_systick: Use clock inputs instead of system_clock_scale Peter Maydell
2021-09-01 10:36 ` [PULL 48/51] hw/arm/stellaris: Fix code style issues in GPTM code Peter Maydell
2021-09-01 10:36 ` [PULL 49/51] hw/arm/stellaris: Split stellaris-gptm into its own file Peter Maydell
2021-09-01 10:36 ` [PULL 50/51] hw/timer/stellaris-gptm: Use Clock input instead of system_clock_scale Peter Maydell
2021-09-01 10:36 ` [PULL 51/51] arm: Remove system_clock_scale global Peter Maydell
2021-09-02  7:48 ` [PULL 00/51] target-arm queue Peter Maydell

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