[PATCH v2 0/3] Introduce clocksource driver for Keystone platform

[PATCH v2 0/3] Introduce clocksource driver for Keystone platform

[Ivan Khoronzhuk]

Add a broadcast timer64 based clockevent driver for keystone arch.
This driver uses timer in 64-bit general purpose mode as clock event
device.

Documentation:
    http://www.ti.com/lit/ug/sprugv5a/sprugv5a.pdf

Based on
git://git.kernel.org/pub/scm/linux/kernel/git/ssantosh/linux-keystone.git
keystone/master

v1..v2:
- clocksource: timer-keystone: introduce clocksource driver for
	renamed timer on "timer-keystone"
	in keystone_timer_interrupt() evet pointer is passed via "dev_id"
	used __relaxed variants of writel/readl and added explicit barriers
	added "keystone_timer_disable()" for using in keystone_set_mode()
	keystone_timer_config() is not used for disabling the timer any more
	in case of an unsupported mode the keystone_timer_config() returns -1.
	used request_irq() instead of setup_irq()
	assigned irq for event_device in event_dev->irq
	calculated timer.hz_period for CLOCK_EVT_MODE_PERIODIC at init
	deleted spare call of keystone_timer_config() in keystone_timer_init()

Ivan Khoronzhuk (3):
  clocksource: timer-keystone: introduce clocksource driver for
    Keystone
  clocksource: keystone: add bindings for keystone timer
  arm: dts: keystone: add keystone timer entry

 .../bindings/timer/ti,keystone-timer.txt           |   29 +++
 arch/arm/boot/dts/keystone-clocks.dtsi             |   10 +
 arch/arm/boot/dts/keystone.dtsi                    |    7 +
 drivers/clocksource/Makefile                       |    1 +
 drivers/clocksource/timer-keystone.c               |  233 ++++++++++++++++++++
 5 files changed, 280 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/timer/ti,keystone-timer.txt
 create mode 100644 drivers/clocksource/timer-keystone.c

-- 
1.7.9.5

[PATCH v2 1/3] clocksource: timer-keystone: introduce clocksource driver for Keystone

[Ivan Khoronzhuk]

Add broadcast clock-event device for the Keystone arch.

The timer can be configured as a general-purpose 64-bit timer,
dual general-purpose 32-bit timers. When configured as dual 32-bit
timers, each half can operate in conjunction (chain mode) or
independently (unchained mode) of each other.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
---
 drivers/clocksource/Makefile         |    1 +
 drivers/clocksource/timer-keystone.c |  233 ++++++++++++++++++++++++++++++++++
 2 files changed, 234 insertions(+)
 create mode 100644 drivers/clocksource/timer-keystone.c

diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index 33621ef..2acf3fc 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -36,3 +36,4 @@ obj-$(CONFIG_ARM_ARCH_TIMER)		+= arm_arch_timer.o
 obj-$(CONFIG_ARM_GLOBAL_TIMER)		+= arm_global_timer.o
 obj-$(CONFIG_CLKSRC_METAG_GENERIC)	+= metag_generic.o
 obj-$(CONFIG_ARCH_HAS_TICK_BROADCAST)	+= dummy_timer.o
+obj-$(CONFIG_ARCH_KEYSTONE)		+= timer-keystone.o
diff --git a/drivers/clocksource/timer-keystone.c b/drivers/clocksource/timer-keystone.c
new file mode 100644
index 0000000..34c6ab8
--- /dev/null
+++ b/drivers/clocksource/timer-keystone.c
@@ -0,0 +1,233 @@
+/*
+ * Keystone broadcast clock-event
+ *
+ * Copyright 2013 Texas Instruments, Inc.
+ *
+ * Author: Ivan Khoronzhuk <ivan.khoronzhuk@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 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/clk.h>
+#include <linux/clockchips.h>
+#include <linux/clocksource.h>
+#include <linux/interrupt.h>
+#include <linux/of_address.h>
+#include <linux/of_irq.h>
+
+#define TIMER_NAME			"timer-keystone"
+
+/* Timer register offsets */
+#define TIM12				0x10
+#define TIM34				0x14
+#define PRD12				0x18
+#define PRD34				0x1c
+#define TCR				0x20
+#define TGCR				0x24
+#define INTCTLSTAT			0x44
+
+/* Timer register bitfields */
+#define TCR_ENAMODE_MASK		0xC0
+#define TCR_ENAMODE_ONESHOT_MASK	0x40
+#define TCR_ENAMODE_PERIODIC_MASK	0x80
+
+#define TGCR_TIM_UNRESET_MASK		0x03
+#define INTCTLSTAT_ENINT_MASK		0x01
+
+/**
+ * struct keystone_timer: holds timer's data
+ * @base: timer memory base address
+ * @period: source clock rate
+ * @irqacrion: interrupt action descriptor
+ * @event_dev: event device based on timer
+ */
+static struct keystone_timer {
+	u64 hz_period;
+	void __iomem *base;
+	struct clock_event_device event_dev;
+} timer;
+
+static inline u32 keystone_timer_readl(unsigned long rg)
+{
+	return readl_relaxed(timer.base + rg);
+}
+
+static inline void keystone_timer_writel(u32 val, unsigned long rg)
+{
+	writel_relaxed(val, timer.base + rg);
+}
+
+/**
+ * keystone_timer_config: configures timer to work in oneshot/periodic modes.
+ * @ mode: mode to configure
+ * @ period: cycles number to configure for
+ */
+static int keystone_timer_config(u64 period, enum clock_event_mode mode)
+{
+	u32 tcr;
+	u32 off;
+
+	tcr = keystone_timer_readl(TCR);
+	off = tcr & ~(TCR_ENAMODE_MASK);
+
+	/* set enable mode */
+	switch (mode) {
+	case CLOCK_EVT_MODE_ONESHOT:
+		tcr |= TCR_ENAMODE_ONESHOT_MASK;
+		break;
+	case CLOCK_EVT_MODE_PERIODIC:
+		tcr |= TCR_ENAMODE_PERIODIC_MASK;
+		break;
+	default:
+		return -1;
+	}
+
+	/* disable timer */
+	keystone_timer_writel(off, TCR);
+	/* here we have to be sure the timer has been disabled */
+	wmb();
+
+	/* reset counter to zero, set new period */
+	keystone_timer_writel(0, TIM12);
+	keystone_timer_writel(0, TIM34);
+	keystone_timer_writel(period & 0xffffffff, PRD12);
+	keystone_timer_writel(period >> 32, PRD34);
+
+	/* enable timer
+	 * here we have to be sure that CNTLO, CNTHI, PRDLO, PRDHI registers
+	 * have been written.
+	 */
+	wmb();
+	keystone_timer_writel(tcr, TCR);
+	return 0;
+}
+
+static void keystone_timer_disable(void)
+{
+	u32 tcr;
+
+	tcr = keystone_timer_readl(TCR);
+
+	/* disable timer */
+	tcr &= ~(TCR_ENAMODE_MASK);
+	keystone_timer_writel(tcr, TCR);
+}
+
+static irqreturn_t keystone_timer_interrupt(int irq, void *dev_id)
+{
+	struct clock_event_device *evt = dev_id;
+
+	evt->event_handler(evt);
+	return IRQ_HANDLED;
+}
+
+static int keystone_set_next_event(unsigned long cycles,
+				  struct clock_event_device *evt)
+{
+	return keystone_timer_config(cycles, evt->mode);
+}
+
+static void keystone_set_mode(enum clock_event_mode mode,
+			     struct clock_event_device *evt)
+{
+	switch (mode) {
+	case CLOCK_EVT_MODE_PERIODIC:
+		keystone_timer_config(timer.hz_period, CLOCK_EVT_MODE_PERIODIC);
+		break;
+	case CLOCK_EVT_MODE_UNUSED:
+	case CLOCK_EVT_MODE_SHUTDOWN:
+	case CLOCK_EVT_MODE_ONESHOT:
+		keystone_timer_disable();
+		break;
+	default:
+		break;
+	}
+}
+
+static void __init keystone_timer_init(struct device_node *np)
+{
+	struct clock_event_device *event_dev = &timer.event_dev;
+	unsigned long rate;
+	struct clk *clk;
+	int irq, error;
+	u32 tgcr;
+
+	irq  = irq_of_parse_and_map(np, 0);
+	if (irq == NO_IRQ) {
+		pr_err("%s: failed to map interrupts\n", __func__);
+		return;
+	}
+
+	timer.base = of_iomap(np, 0);
+	if (!timer.base) {
+		pr_err("%s: failed to map registers\n", __func__);
+		return;
+	}
+
+	clk = of_clk_get(np, 0);
+	if (!clk) {
+		pr_err("%s: failed to get clock\n", __func__);
+		iounmap(timer.base);
+		return;
+	}
+
+	error = clk_prepare_enable(clk);
+	if (error) {
+		pr_err("%s: failed to enable clock\n", __func__);
+		goto err;
+	}
+
+	rate = clk_get_rate(clk);
+
+	/* disable, use internal clock source */
+	keystone_timer_writel(0, TCR);
+	/* here we have to be sure the timer has been disabled */
+	wmb();
+
+	/* reset timer as 64-bit, no pre-scaler, plus features are disabled */
+	tgcr = 0;
+	keystone_timer_writel(0, TGCR);
+
+	/* unreset timer */
+	tgcr |= TGCR_TIM_UNRESET_MASK;
+	keystone_timer_writel(tgcr, TGCR);
+
+	/* init counter to zero */
+	keystone_timer_writel(0, TIM12);
+	keystone_timer_writel(0, TIM34);
+
+	timer.hz_period = rate / (HZ);
+
+	/* enable timer interrupts */
+	keystone_timer_writel(INTCTLSTAT_ENINT_MASK, INTCTLSTAT);
+
+	error = request_irq(irq, keystone_timer_interrupt, IRQF_TIMER,
+			    TIMER_NAME, event_dev);
+	if (error) {
+		pr_err("%s: failed to setup irq\n", __func__);
+		goto err;
+	}
+
+	/* setup clockevent */
+	event_dev->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT;
+	event_dev->set_next_event = keystone_set_next_event;
+	event_dev->set_mode = keystone_set_mode;
+	event_dev->cpumask = cpu_all_mask;
+	event_dev->owner = THIS_MODULE;
+	event_dev->name = TIMER_NAME;
+	event_dev->irq = irq;
+
+	clockevents_config_and_register(event_dev, rate, 1, ULONG_MAX);
+
+	pr_info("keystone timer clock @%lu Hz\n", rate);
+	return;
+err:
+	clk_put(clk);
+	iounmap(timer.base);
+}
+
+CLOCKSOURCE_OF_DECLARE(keystone_timer, "ti,keystone-timer",
+					keystone_timer_init);
-- 
1.7.9.5

[PATCH v2 2/3] clocksource: keystone: add bindings for keystone timer

[Ivan Khoronzhuk]

This patch provides bindings for the 64-bit timer in the KeyStone
architecture devices. The timer can be configured as a general-purpose 64-bit
timer, dual general-purpose 32-bit timers. When configured as dual 32-bit
timers, each half can operate in conjunction (chain mode) or independently
(unchained mode) of each other.

It is global timer is a free running up-counter and can generate interrupt
when the counter reaches preset counter values.

Documentation:
http://www.ti.com/lit/ug/sprugv5a/sprugv5a.pdf

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
---
 .../bindings/timer/ti,keystone-timer.txt           |   29 ++++++++++++++++++++
 1 file changed, 29 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/timer/ti,keystone-timer.txt

diff --git a/Documentation/devicetree/bindings/timer/ti,keystone-timer.txt b/Documentation/devicetree/bindings/timer/ti,keystone-timer.txt
new file mode 100644
index 0000000..5fbe361
--- /dev/null
+++ b/Documentation/devicetree/bindings/timer/ti,keystone-timer.txt
@@ -0,0 +1,29 @@
+* Device tree bindings for Texas instruments Keystone timer
+
+This document provides bindings for the 64-bit timer in the KeyStone
+architecture devices. The timer can be configured as a general-purpose 64-bit
+timer, dual general-purpose 32-bit timers. When configured as dual 32-bit
+timers, each half can operate in conjunction (chain mode) or independently
+(unchained mode) of each other.
+
+It is global timer is a free running up-counter and can generate interrupt
+when the counter reaches preset counter values.
+
+Documentation:
+http://www.ti.com/lit/ug/sprugv5a/sprugv5a.pdf
+
+Required properties:
+
+- compatible : should be "ti,keystone-timer".
+- reg : specifies base physical address and count of the registers.
+- interrupts : interrupt generated by the timer.
+- clocks : the clock feeding the timer clock.
+
+Example:
+
+timer at 22f0000 {
+	compatible = "ti,keystone-timer";
+	reg = <0x022f0000 0x80>;
+	interrupts = <GIC_SPI 110 IRQ_TYPE_EDGE_RISING>;
+	clocks = <&clktimer15>;
+};
-- 
1.7.9.5

[PATCH v2 3/3] arm: dts: keystone: add keystone timer entry

[Ivan Khoronzhuk]

Add keystone timer entry to keystone device tree.
This 64-bit timer is used as backup clock event device.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
---
 arch/arm/boot/dts/keystone-clocks.dtsi |   10 ++++++++++
 arch/arm/boot/dts/keystone.dtsi        |    7 +++++++
 2 files changed, 17 insertions(+)

diff --git a/arch/arm/boot/dts/keystone-clocks.dtsi b/arch/arm/boot/dts/keystone-clocks.dtsi
index 2363593..16d2aba 100644
--- a/arch/arm/boot/dts/keystone-clocks.dtsi
+++ b/arch/arm/boot/dts/keystone-clocks.dtsi
@@ -737,6 +737,16 @@ clocks {
 		domain-id = <0>;
 	};
 
+	clktimer15: clktimer15 {
+		#clock-cells = <0>;
+		compatible = "ti,keystone,psc-clock";
+		clocks = <&clkmodrst0>;
+		clock-output-names = "timer15";
+		reg = <0x02350000 0xb00>, <0x02350000 0x400>;
+		reg-names = "control", "domain";
+		domain-id = <0>;
+	};
+
 	clkuart0: clkuart0 {
 		#clock-cells = <0>;
 		compatible = "ti,keystone,psc-clock";
diff --git a/arch/arm/boot/dts/keystone.dtsi b/arch/arm/boot/dts/keystone.dtsi
index f6d6d9e..3f05c07 100644
--- a/arch/arm/boot/dts/keystone.dtsi
+++ b/arch/arm/boot/dts/keystone.dtsi
@@ -181,5 +181,12 @@
 			interrupts = <GIC_SPI 300 IRQ_TYPE_EDGE_RISING>;
 			clocks = <&clkspi>;
 		};
+
+		clock_event: timer at 22f0000 {
+			compatible = "ti,keystone-timer";
+			reg = <0x022f0000 0x80>;
+			interrupts = <GIC_SPI 110 IRQ_TYPE_EDGE_RISING>;
+			clocks = <&clktimer15>;
+		};
 	};
 };
-- 
1.7.9.5

[PATCH v2 1/3] clocksource: timer-keystone: introduce clocksource driver for Keystone

[Santosh Shilimkar]

On Tuesday 17 December 2013 11:22 AM, Ivan Khoronzhuk wrote:
> Add broadcast clock-event device for the Keystone arch.
> 
> The timer can be configured as a general-purpose 64-bit timer,
> dual general-purpose 32-bit timers. When configured as dual 32-bit
> timers, each half can operate in conjunction (chain mode) or
> independently (unchained mode) of each other.
> 
> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
> ---
>  drivers/clocksource/Makefile         |    1 +
>  drivers/clocksource/timer-keystone.c |  233 ++++++++++++++++++++++++++++++++++
>  2 files changed, 234 insertions(+)
>  create mode 100644 drivers/clocksource/timer-keystone.c
> 
> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> index 33621ef..2acf3fc 100644
> --- a/drivers/clocksource/Makefile
> +++ b/drivers/clocksource/Makefile
> @@ -36,3 +36,4 @@ obj-$(CONFIG_ARM_ARCH_TIMER)		+= arm_arch_timer.o
>  obj-$(CONFIG_ARM_GLOBAL_TIMER)		+= arm_global_timer.o
>  obj-$(CONFIG_CLKSRC_METAG_GENERIC)	+= metag_generic.o
>  obj-$(CONFIG_ARCH_HAS_TICK_BROADCAST)	+= dummy_timer.o
> +obj-$(CONFIG_ARCH_KEYSTONE)		+= timer-keystone.o
> diff --git a/drivers/clocksource/timer-keystone.c b/drivers/clocksource/timer-keystone.c
> new file mode 100644
> index 0000000..34c6ab8
> --- /dev/null
> +++ b/drivers/clocksource/timer-keystone.c
> @@ -0,0 +1,233 @@
> +/*
> + * Keystone broadcast clock-event
> + *
> + * Copyright 2013 Texas Instruments, Inc.
> + *
> + * Author: Ivan Khoronzhuk <ivan.khoronzhuk@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 as
> + * published by the Free Software Foundation.
> + *
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/clockchips.h>
> +#include <linux/clocksource.h>
> +#include <linux/interrupt.h>
> +#include <linux/of_address.h>
> +#include <linux/of_irq.h>
> +
> +#define TIMER_NAME			"timer-keystone"
> +
> +/* Timer register offsets */
> +#define TIM12				0x10
> +#define TIM34				0x14
> +#define PRD12				0x18
> +#define PRD34				0x1c
> +#define TCR				0x20
> +#define TGCR				0x24
> +#define INTCTLSTAT			0x44
> +
> +/* Timer register bitfields */
> +#define TCR_ENAMODE_MASK		0xC0
> +#define TCR_ENAMODE_ONESHOT_MASK	0x40
> +#define TCR_ENAMODE_PERIODIC_MASK	0x80
> +
> +#define TGCR_TIM_UNRESET_MASK		0x03
> +#define INTCTLSTAT_ENINT_MASK		0x01
> +
> +/**
> + * struct keystone_timer: holds timer's data
> + * @base: timer memory base address
> + * @period: source clock rate
> + * @irqacrion: interrupt action descriptor
> + * @event_dev: event device based on timer
> + */
> +static struct keystone_timer {
> +	u64 hz_period;
> +	void __iomem *base;
> +	struct clock_event_device event_dev;
> +} timer;
> +
> +static inline u32 keystone_timer_readl(unsigned long rg)
> +{
> +	return readl_relaxed(timer.base + rg);
> +}
> +
> +static inline void keystone_timer_writel(u32 val, unsigned long rg)
> +{
> +	writel_relaxed(val, timer.base + rg);
> +}
> +
> +/**
> + * keystone_timer_config: configures timer to work in oneshot/periodic modes.
> + * @ mode: mode to configure
> + * @ period: cycles number to configure for
> + */
> +static int keystone_timer_config(u64 period, enum clock_event_mode mode)
> +{
> +	u32 tcr;
> +	u32 off;
> +
> +	tcr = keystone_timer_readl(TCR);
> +	off = tcr & ~(TCR_ENAMODE_MASK);
> +
> +	/* set enable mode */
> +	switch (mode) {
> +	case CLOCK_EVT_MODE_ONESHOT:
> +		tcr |= TCR_ENAMODE_ONESHOT_MASK;
> +		break;
> +	case CLOCK_EVT_MODE_PERIODIC:
> +		tcr |= TCR_ENAMODE_PERIODIC_MASK;
> +		break;
> +	default:
> +		return -1;
> +	}
> +
> +	/* disable timer */
> +	keystone_timer_writel(off, TCR);
> +	/* here we have to be sure the timer has been disabled */
> +	wmb();
> +
> +	/* reset counter to zero, set new period */
> +	keystone_timer_writel(0, TIM12);
> +	keystone_timer_writel(0, TIM34);
> +	keystone_timer_writel(period & 0xffffffff, PRD12);
> +	keystone_timer_writel(period >> 32, PRD34);
> +
> +	/* enable timer
> +	 * here we have to be sure that CNTLO, CNTHI, PRDLO, PRDHI registers
> +	 * have been written.
> +	 */
Comment style ?
/*
 *
 */

Other than the minor comment. The patch looks fine to me..
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

[PATCH v2 2/3] clocksource: keystone: add bindings for keystone timer

[Santosh Shilimkar]

On Tuesday 17 December 2013 11:22 AM, Ivan Khoronzhuk wrote:
> This patch provides bindings for the 64-bit timer in the KeyStone
> architecture devices. The timer can be configured as a general-purpose 64-bit
> timer, dual general-purpose 32-bit timers. When configured as dual 32-bit
> timers, each half can operate in conjunction (chain mode) or independently
> (unchained mode) of each other.
> 
> It is global timer is a free running up-counter and can generate interrupt
> when the counter reaches preset counter values.
> 
> Documentation:
> http://www.ti.com/lit/ug/sprugv5a/sprugv5a.pdf
> 
> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
> ---
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

[PATCH v2 3/3] arm: dts: keystone: add keystone timer entry

[Santosh Shilimkar]

On Tuesday 17 December 2013 11:22 AM, Ivan Khoronzhuk wrote:
> Add keystone timer entry to keystone device tree.
> This 64-bit timer is used as backup clock event device.
> 
> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
> ---
I can pick this up once patch 1 and 2 are picked up.
Thanks for the Patches Ivan.

Regards,
Santosh

[PATCH v2 1/3] clocksource: timer-keystone: introduce clocksource driver for Keystone

[Stephen Boyd]

On 12/17, Ivan Khoronzhuk wrote:
> +static void __init keystone_timer_init(struct device_node *np)
> +{
> +	struct clock_event_device *event_dev = &timer.event_dev;
> +	unsigned long rate;
[...]
> +
> +	timer.hz_period = rate / (HZ);

Unnecessary parentheses here. Also, do you need to use do_div()
here? I'm lost how the hz_period is ever greater than 32 bits
though because HZ is most likely very small and the rate is
unsigned long.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by The Linux Foundation

[PATCH v2 1/3] clocksource: timer-keystone: introduce clocksource driver for Keystone

[ivan.khoronzhuk]

On 12/24/2013 02:58 AM, Stephen Boyd wrote:
> On 12/17, Ivan Khoronzhuk wrote:
>> +static void __init keystone_timer_init(struct device_node *np)
>> +{
>> +	struct clock_event_device *event_dev = &timer.event_dev;
>> +	unsigned long rate;
> [...]
>> +
>> +	timer.hz_period = rate / (HZ);
>
> Unnecessary parentheses here. Also, do you need to use do_div()
> here? I'm lost how the hz_period is ever greater than 32 bits
> though because HZ is most likely very small and the rate is
> unsigned long.
>

You are right.
I'll do the following:

timer.hz_period = rate / (HZ)	---> timer.hz_period = rate / HZ
u64 hz_period			---> unsigned long hz_period

-- 
Regards,
Ivan Khoronzhuk

[PATCH v2 1/3] clocksource: timer-keystone: introduce clocksource driver for Keystone

[ivan.khoronzhuk]

On 12/24/2013 10:36 AM, ivan.khoronzhuk wrote:
> On 12/24/2013 02:58 AM, Stephen Boyd wrote:
>> On 12/17, Ivan Khoronzhuk wrote:
>>> +static void __init keystone_timer_init(struct device_node *np)
>>> +{
>>> +    struct clock_event_device *event_dev = &timer.event_dev;
>>> +    unsigned long rate;
>> [...]
>>> +
>>> +    timer.hz_period = rate / (HZ);
>>
>> Unnecessary parentheses here. Also, do you need to use do_div()
>> here? I'm lost how the hz_period is ever greater than 32 bits
>> though because HZ is most likely very small and the rate is
>> unsigned long.
>>
> 
> You are right.
> I'll do the following:
> 
> timer.hz_period = rate / (HZ)    ---> timer.hz_period = rate / HZ
> u64 hz_period            ---> unsigned long hz_period
> 

... maybe it be better to use DIV_ROUND_UP to be sure in no less than HZ period:

timer.hz_period = rate / (HZ) --> timer.hz_period = DIV_ROUND_UP(rate, HZ)

-- 
Regards,
Ivan Khoronzhuk