[RFC/PATCH 09/11] clocksource: add TI 32.768 Hz counter driver

[Felipe Balbi]

Introduce a new clocksource driver for Texas
Instruments 32.768 Hz device which is available
on most OMAP-like devices.

Signed-off-by: Felipe Balbi <balbi@xxxxxx>
---
 drivers/clocksource/Kconfig        |   8 +++
 drivers/clocksource/Makefile       |   1 +
 drivers/clocksource/timer-ti-32k.c | 121 +++++++++++++++++++++++++++++++++++++
 3 files changed, 130 insertions(+)
 create mode 100644 drivers/clocksource/timer-ti-32k.c

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index a7726db13abb..0ccfd12a00a3 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -115,6 +115,14 @@ config CLKSRC_PISTACHIO
 	bool
 	select CLKSRC_OF
 
+config CLKSRC_TI_32K
+	bool "Texas Instruments 32.768 Hz Clocksource"
+	depends on OF && ARCH_OMAP2PLUS
+	select CLKSRC_OF
+	help
+	  This option enables support for Texas Instruments 32.768 Hz clocksource
+	  available on many OMAP-like platforms.
+
 config CLKSRC_STM32
 	bool "Clocksource for STM32 SoCs" if !ARCH_STM32
 	depends on OF && ARM && (ARCH_STM32 || COMPILE_TEST)
diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index 5c00863c3e33..749abc3665b3 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -45,6 +45,7 @@ obj-$(CONFIG_VF_PIT_TIMER)	+= vf_pit_timer.o
 obj-$(CONFIG_CLKSRC_QCOM)	+= qcom-timer.o
 obj-$(CONFIG_MTK_TIMER)		+= mtk_timer.o
 obj-$(CONFIG_CLKSRC_PISTACHIO)	+= time-pistachio.o
+obj-$(CONFIG_CLKSRC_TI_32K)	+= timer-ti-32k.o
 
 obj-$(CONFIG_ARM_ARCH_TIMER)		+= arm_arch_timer.o
 obj-$(CONFIG_ARM_GLOBAL_TIMER)		+= arm_global_timer.o
diff --git a/drivers/clocksource/timer-ti-32k.c b/drivers/clocksource/timer-ti-32k.c
new file mode 100644
index 000000000000..10ccce2eb645
--- /dev/null
+++ b/drivers/clocksource/timer-ti-32k.c
@@ -0,0 +1,121 @@
+/**
+ * timer-ti-32k.c - OMAP2 32k Timer Support
+ *
+ * Copyright (C) 2015 Texas Instruments Incorporated - http://www.ti.com
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2  of
+ * the License 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/init.h>
+#include <linux/time.h>
+#include <linux/interrupt.h>
+#include <linux/err.h>
+#include <linux/irq.h>
+#include <linux/sched_clock.h>
+#include <linux/clocksource.h>
+#include <linux/slab.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/of_irq.h>
+
+#include <asm/mach/time.h>
+
+/* OMAP2_32KSYNCNT_CR_OFF: offset of 32ksync counter register */
+#define OMAP2_32KSYNCNT_REV_OFF		0x0
+#define OMAP2_32KSYNCNT_REV_SCHEME	(0x3 << 30)
+#define OMAP2_32KSYNCNT_CR_OFF_LOW	0x10
+#define OMAP2_32KSYNCNT_CR_OFF_HIGH	0x30
+
+/*
+ * 32KHz clocksource ... always available, on pretty most chips except
+ * OMAP 730 and 1510.  Other timers could be used as clocksources, with
+ * higher resolution in free-running counter modes (e.g. 12 MHz xtal),
+ * but systems won't necessarily want to spend resources that way.
+ */
+static void __iomem *sync32k_cnt_reg;
+
+/**
+ * omap_read_persistent_clock64 -  Return time from a persistent clock.
+ *
+ * Reads the time from a source which isn't disabled during PM, the
+ * 32k sync timer.  Convert the cycles elapsed since last read into
+ * nsecs and adds to a monotonically increasing timespec64.
+ */
+static struct timespec64 persistent_ts;
+static cycles_t cycles;
+static unsigned int persistent_mult, persistent_shift;
+
+static u64 notrace omap_32k_read_sched_clock(void)
+{
+	return readl_relaxed(sync32k_cnt_reg);
+}
+
+static void omap_read_persistent_clock64(struct timespec64 *ts)
+{
+	unsigned long long nsecs;
+	cycles_t last_cycles;
+
+	last_cycles = cycles;
+	cycles = sync32k_cnt_reg ? readl_relaxed(sync32k_cnt_reg) : 0;
+
+	nsecs = clocksource_cyc2ns(cycles - last_cycles,
+					persistent_mult, persistent_shift);
+
+	timespec64_add_ns(&persistent_ts, nsecs);
+
+	*ts = persistent_ts;
+}
+
+static void __init ti_32k_timer_init(struct device_node *np)
+{
+	void __iomem *vbase;
+	int ret;
+
+	vbase = of_iomap(np, 0);
+	if (!vbase) {
+		pr_err("Can't ioremap 32k timer base\n");
+		return;
+	}
+
+	/*
+	 * 32k sync Counter IP register offsets vary between the
+	 * highlander version and the legacy ones.
+	 * The 'SCHEME' bits(30-31) of the revision register is used
+	 * to identify the version.
+	 */
+	if (readl_relaxed(vbase + OMAP2_32KSYNCNT_REV_OFF) &
+						OMAP2_32KSYNCNT_REV_SCHEME)
+		sync32k_cnt_reg = vbase + OMAP2_32KSYNCNT_CR_OFF_HIGH;
+	else
+		sync32k_cnt_reg = vbase + OMAP2_32KSYNCNT_CR_OFF_LOW;
+
+	/*
+	 * 120000 rough estimate from the calculations in
+	 * __clocksource_update_freq_scale.
+	 */
+	clocks_calc_mult_shift(&persistent_mult, &persistent_shift,
+			32768, NSEC_PER_SEC, 120000);
+
+	ret = clocksource_mmio_init(sync32k_cnt_reg, "32k_counter", 32768,
+				250, 32, clocksource_mmio_readl_up);
+	if (ret) {
+		pr_err("32k_counter: can't register clocksource\n");
+		return;
+	}
+
+	sched_clock_register(omap_32k_read_sched_clock, 32, 32768);
+	register_persistent_clock(NULL, omap_read_persistent_clock64);
+	pr_info("OMAP clocksource: 32k_counter at 32768 Hz\n");
+}
+CLOCKSOURCE_OF_DECLARE(ti_32k_timer, "ti,omap-counter32k",
+		ti_32k_timer_init);
-- 
2.5.3

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