Add a simple delay timer driver API

The API is simple. The BSP or specific timer driver creates an
instance of timer_ops_t, fills in the timer specific data, then calls
timer_init(). The timer specific data includes a function pointer
to return the timer value and a clock multiplier/divider. The ratio
of the multiplier and the divider is the clock frequency in MHz.

After that, mdelay() or udelay() can be called to delay execution for
the specified time (milliseconds or microseconds, respectively).

Change-Id: Icf8a295e1d25874f789bf28b7412156329dc975c
Co-authored-by: Dan Handley <dan.handley@arm.com>

drivers/delay_timer/delay_timer.c

+/*
+ * Copyright (c) 2015, ARM Limited and Contributors. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * Redistributions of source code must retain the above copyright notice, this
+ * list of conditions and the following disclaimer.
+ *
+ * Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ *
+ * Neither the name of ARM nor the names of its contributors may be used
+ * to endorse or promote products derived from this software without specific
+ * prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <assert.h>
+#include <delay_timer.h>
+#include <platform_def.h>
+
+/***********************************************************
+ * The delay timer implementation
+ ***********************************************************/
+static const timer_ops_t *ops;
+
+/***********************************************************
+ * Delay for the given number of microseconds. The driver must
+ * be initialized before calling this function.
+ ***********************************************************/
+void udelay(uint32_t usec)
+{
+	assert(ops != 0 &&
+		(ops->clk_mult != 0) &&
+		(ops->clk_div != 0) &&
+		(ops->get_timer_value != 0));
+
+	uint32_t start, cnt, delta, delta_us;
+
+	/* counter is decreasing */
+	start = ops->get_timer_value();
+	do {
+		cnt = ops->get_timer_value();
+		if (cnt > start) {
+			delta = UINT32_MAX - cnt;
+			delta += start;
+		} else
+			delta = start - cnt;
+		delta_us = (delta * ops->clk_mult) / ops->clk_div;
+	} while (delta_us < usec);
+}
+
+/***********************************************************
+ * Delay for the given number of milliseconds. The driver must
+ * be initialized before calling this function.
+ ***********************************************************/
+void mdelay(uint32_t msec)
+{
+	udelay(msec*1000);
+}
+
+/***********************************************************
+ * Initialize the timer. The fields in the provided timer
+ * ops pointer must be valid.
+ ***********************************************************/
+void timer_init(const timer_ops_t *ops_ptr)
+{
+	assert(ops_ptr != 0  &&
+		(ops_ptr->clk_mult != 0) &&
+		(ops_ptr->clk_div != 0) &&
+		(ops_ptr->get_timer_value != 0));
+
+	ops = ops_ptr;
+}

include/drivers/delay_timer.h

+/*
+ * Copyright (c) 2015, ARM Limited and Contributors. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * Redistributions of source code must retain the above copyright notice, this
+ * list of conditions and the following disclaimer.
+ *
+ * Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ *
+ * Neither the name of ARM nor the names of its contributors may be used
+ * to endorse or promote products derived from this software without specific
+ * prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef __DELAY_TIMER_H__
+#define __DELAY_TIMER_H__
+
+#include <stdint.h>
+
+/********************************************************************
+ * A simple timer driver providing synchronous delay functionality.
+ * The driver must be initialized with a structure that provides a
+ * function pointer to return the timer value and a clock
+ * multiplier/divider. The ratio of the multiplier and the divider is
+ * the clock frequency in MHz.
+ ********************************************************************/
+
+typedef struct timer_ops {
+	uint32_t (*get_timer_value)(void);
+	uint32_t clk_mult;
+	uint32_t clk_div;
+} timer_ops_t;
+
+void mdelay(uint32_t msec);
+void udelay(uint32_t usec);
+void timer_init(const timer_ops_t *ops);
+
+
+#endif /* __DELAY_TIMER_H__ */