Implement generic delay timer

Add delay timer implementation based on the system generic counter.
This either uses the platform's implementation of
`plat_get_syscnt_freq()` or explicit clock multiplier/divider values
provided by the platform.

The current implementation of udelay has been modified to avoid
unnecessary calculations while waiting on the loop and to make it
easier to check for overflows.

Change-Id: I9062e1d506dc2f68367fd9289250b93444721732

2 files changed, 95 insertions, 10 deletions

diff --git a/drivers/delay_timer/delay_timer.c b/drivers/delay_timer/delay_timer.c
index 0bee876f..ed7ed52e 100644
--- a/drivers/delay_timer/delay_timer.c
+++ b/drivers/delay_timer/delay_timer.c
@@ -48,19 +48,22 @@ void udelay(uint32_t usec)
 		(ops->clk_div != 0) &&
 		(ops->get_timer_value != 0));
 
-	uint32_t start, cnt, delta, delta_us;
+	uint32_t start, delta, total_delta;
+
+	assert(usec < UINT32_MAX / ops->clk_div);
 
-	/* counter is decreasing */
 	start = ops->get_timer_value();
+
+	total_delta = (usec * ops->clk_div) / ops->clk_mult;
+
 	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);
+		/*
+		 * If the timer value wraps around, the subtraction will
+		 * overflow and it will still give the correct result.
+		 */
+		delta = start - ops->get_timer_value(); /* Decreasing counter */
+
+	} while (delta < total_delta);
 }
 
 /***********************************************************
diff --git a/drivers/delay_timer/generic_delay_timer.c b/drivers/delay_timer/generic_delay_timer.c
new file mode 100644
index 00000000..4c364a30
--- /dev/null
+++ b/drivers/delay_timer/generic_delay_timer.c
@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2016, 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 <arch_helpers.h>
+#include <assert.h>
+#include <bl_common.h>
+#include <debug.h>
+#include <delay_timer.h>
+#include <platform.h>
+
+/* Ticks elapsed in one second by a signal of 1 MHz */
+#define MHZ_TICKS_PER_SEC 1000000
+
+static timer_ops_t ops;
+
+static uint32_t get_timer_value(void)
+{
+	/*
+	 * Generic delay timer implementation expects the timer to be a down
+	 * counter. We apply bitwise NOT operator to the tick values returned
+	 * by read_cntpct_el0() to simulate the down counter. The value is
+	 * clipped from 64 to 32 bits.
+	 */
+	return (uint32_t)(~read_cntpct_el0());
+}
+
+void generic_delay_timer_init_args(uint32_t mult, uint32_t div)
+{
+	ops.get_timer_value	= get_timer_value;
+	ops.clk_mult		= mult;
+	ops.clk_div		= div;
+
+	timer_init(&ops);
+
+	VERBOSE("Generic delay timer configured with mult=%u and div=%u\n",
+		mult, div);
+}
+
+void generic_delay_timer_init(void)
+{
+	/* Value in ticks */
+	unsigned int mult = MHZ_TICKS_PER_SEC;
+
+	/* Value in ticks per second (Hz) */
+	unsigned int div  = plat_get_syscnt_freq2();
+
+	/* Reduce multiplier and divider by dividing them repeatedly by 10 */
+	while ((mult % 10 == 0) && (div % 10 == 0)) {
+		mult /= 10;
+		div /= 10;
+	}
+
+	generic_delay_timer_init_args(mult, div);
+}
+