hw/timer/sse-counter: Model the SSE Subsystem System Counter

The SSE-300 includes a counter module; implement a model of it.

This counter is documented in the SSE-123 Example Subsystem
Technical Reference Manual:
 https://developer.arm.com/documentation/101370/latest/

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>
Message-id: 20210219144617.4782-12-peter.maydell@linaro.org

include/hw/timer/sse-counter.h

@@ -0,0 +1,105 @@
+/*
+ * Arm SSE Subsystem System Counter
+ *
+ * Copyright (c) 2020 Linaro Limited
+ * Written by Peter Maydell
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 or
+ * (at your option) any later version.
+ */
+
+/*
+ * This is a model of the "System counter" which is documented in
+ * the Arm SSE-123 Example Subsystem Technical Reference Manual:
+ * https://developer.arm.com/documentation/101370/latest/
+ *
+ * QEMU interface:
+ *  + Clock input "CLK": clock
+ *  + sysbus MMIO region 0: the control register frame
+ *  + sysbus MMIO region 1: the status register frame
+ *
+ * Consumers of the system counter's timestamp, such as the SSE
+ * System Timer device, can also use the APIs sse_counter_for_timestamp(),
+ * sse_counter_tick_to_time() and sse_counter_register_consumer() to
+ * interact with an instance of the System Counter. Generally the
+ * consumer device should have a QOM link property which the board
+ * code can set to the appropriate instance of the system counter.
+ */
+
+#ifndef SSE_COUNTER_H
+#define SSE_COUNTER_H
+
+#include "hw/sysbus.h"
+#include "qom/object.h"
+#include "qemu/notify.h"
+
+#define TYPE_SSE_COUNTER "sse-counter"
+OBJECT_DECLARE_SIMPLE_TYPE(SSECounter, SSE_COUNTER)
+
+struct SSECounter {
+    /*< private >*/
+    SysBusDevice parent_obj;
+
+    /*< public >*/
+    MemoryRegion control_mr;
+    MemoryRegion status_mr;
+    Clock *clk;
+    NotifierList notifier_list;
+
+    uint32_t cntcr;
+    uint32_t cntscr0;
+
+    /*
+     * These are used for handling clock frequency changes: they are a
+     * tuple of (QEMU_CLOCK_VIRTUAL timestamp, CNTCV at that time),
+     * taken when the clock frequency changes. sse_cntcv() needs them
+     * to calculate the current CNTCV.
+     */
+    uint64_t ns_then;
+    uint64_t ticks_then;
+};
+
+/*
+ * These functions are the interface by which a consumer of
+ * the system timestamp (such as the SSE system timer device)
+ * can communicate with the SSECounter.
+ */
+
+/**
+ * sse_counter_for_timestamp:
+ * @counter: SSECounter
+ * @ns: timestamp of QEMU_CLOCK_VIRTUAL in nanoseconds
+ *
+ * Returns the value of the timestamp counter at the specified
+ * point in time (assuming that no changes to scale factor, enable, etc
+ * happen in the meantime).
+ */
+uint64_t sse_counter_for_timestamp(SSECounter *counter, uint64_t ns);
+
+/**
+ * sse_counter_tick_to_time:
+ * @counter: SSECounter
+ * @tick: tick value
+ *
+ * Returns the time (a QEMU_CLOCK_VIRTUAL timestamp in nanoseconds)
+ * when the timestamp counter will reach the specified tick count.
+ * If the counter is not currently running, returns UINT64_MAX.
+ */
+uint64_t sse_counter_tick_to_time(SSECounter *counter, uint64_t tick);
+
+/**
+ * sse_counter_register_consumer:
+ * @counter: SSECounter
+ * @notifier: Notifier which is notified on counter changes
+ *
+ * Registers @notifier with the SSECounter. When the counter's
+ * configuration changes in a way that might invalidate information
+ * previously returned via sse_counter_for_timestamp() or
+ * sse_counter_tick_to_time(), the notifier will be called.
+ * Devices which consume the timestamp counter can use this as
+ * a cue to recalculate timer events.
+ */
+void sse_counter_register_consumer(SSECounter *counter, Notifier *notifier);
+
+#endif