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authorWill Deacon <will.deacon@arm.com>2012-07-06 15:47:17 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2012-07-09 17:42:23 +0100
commitd0a533b18235d36206b9b422efadb7cee444dfdb (patch)
tree43dcdcf9eebd9c88430df031305ca4eb5c2346f4 /arch/arm/lib/delay.c
parent923df96b9f31b7d08d8438ff9677326d9537accf (diff)
ARM: 7452/1: delay: allow timer-based delay implementation to be selected
This patch allows a timer-based delay implementation to be selected by switching the delay routines over to use get_cycles, which is implemented in terms of read_current_timer. This further allows us to skip the loop calibration and have a consistent delay function in the face of core frequency scaling. To avoid the pain of dealing with memory-mapped counters, this implementation uses the co-processor interface to the architected timers when they are available. The previous loop-based implementation is kept around for CPUs without the architected timers and we retain both the maximum delay (2ms) and the corresponding conversion factors for determining the number of loops required for a given interval. Since the indirection of the timer routines will only work when called from C, the sa1100 sleep routines are modified to branch to the loop-based delay functions directly. Tested-by: Shinya Kuribayashi <shinya.kuribayashi.px@renesas.com> Reviewed-by: Stephen Boyd <sboyd@codeaurora.org> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/lib/delay.c')
-rw-r--r--arch/arm/lib/delay.c71
1 files changed, 71 insertions, 0 deletions
diff --git a/arch/arm/lib/delay.c b/arch/arm/lib/delay.c
new file mode 100644
index 00000000000..d6dacc69254
--- /dev/null
+++ b/arch/arm/lib/delay.c
@@ -0,0 +1,71 @@
+/*
+ * Delay loops based on the OpenRISC implementation.
+ *
+ * Copyright (C) 2012 ARM Limited
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ *
+ * Author: Will Deacon <will.deacon@arm.com>
+ */
+
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/timex.h>
+
+/*
+ * Default to the loop-based delay implementation.
+ */
+struct arm_delay_ops arm_delay_ops = {
+ .delay = __loop_delay,
+ .const_udelay = __loop_const_udelay,
+ .udelay = __loop_udelay,
+};
+
+#ifdef ARCH_HAS_READ_CURRENT_TIMER
+static void __timer_delay(unsigned long cycles)
+{
+ cycles_t start = get_cycles();
+
+ while ((get_cycles() - start) < cycles)
+ cpu_relax();
+}
+
+static void __timer_const_udelay(unsigned long xloops)
+{
+ unsigned long long loops = xloops;
+ loops *= loops_per_jiffy;
+ __timer_delay(loops >> UDELAY_SHIFT);
+}
+
+static void __timer_udelay(unsigned long usecs)
+{
+ __timer_const_udelay(usecs * UDELAY_MULT);
+}
+
+void __init init_current_timer_delay(unsigned long freq)
+{
+ pr_info("Switching to timer-based delay loop\n");
+ lpj_fine = freq / HZ;
+ arm_delay_ops.delay = __timer_delay;
+ arm_delay_ops.const_udelay = __timer_const_udelay;
+ arm_delay_ops.udelay = __timer_udelay;
+}
+
+unsigned long __cpuinit calibrate_delay_is_known(void)
+{
+ return lpj_fine;
+}
+#endif