RE: [PATCH 3/4] ARM: Xilinx: Adding timer support to the platform

[John Linn]

> -----Original Message-----
> From: Jamie Iles [mailto:jamie@xxxxxxxxxxxxx]
> Sent: Saturday, February 05, 2011 6:04 PM
> To: John Linn
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
linux-kernel@xxxxxxxxxxxxxxx; linux@xxxxxxxxxxxxxxxx;
> catalin.marinas@xxxxxxx; glikely@xxxxxxxxxxxx; Kiran Sutariya
> Subject: Re: [PATCH 3/4] ARM: Xilinx: Adding timer support to the
platform
> 
> Hi John,
> 
> A couple more nitpicks.
> 
> Jamie
> 
> On Sat, Feb 05, 2011 at 09:17:16AM -0700, John Linn wrote:
> > The timer driver supports the Xilinx PS Timer Counter IP.
> >
> > Signed-off-by: Kiran Sutariya <kiran.sutariya@xxxxxxxxxxxxxx>
> > Signed-off-by: John Linn <john.linn@xxxxxxxxxx>
> > ---
> >  arch/arm/mach-xilinx/timer.c |  452
++++++++++++++++++++++++++++++++++++++++++
> >  1 files changed, 452 insertions(+), 0 deletions(-)
> >  create mode 100644 arch/arm/mach-xilinx/timer.c
> >
> > diff --git a/arch/arm/mach-xilinx/timer.c
b/arch/arm/mach-xilinx/timer.c
> > new file mode 100644
> > index 0000000..c713e3c
> > --- /dev/null
> > +++ b/arch/arm/mach-xilinx/timer.c
> > @@ -0,0 +1,452 @@
> > +/* arch/arm/mach-xilinx/timer.c
> > + *
> > + * This file contains driver for the Xilinx PS Timer Counter IP.
> > + *
> > + *  Copyright (C) 2011 Xilinx
> > + *
> > + * based on arch\mips\kernel\time.c timer driver
> > + *
> > + * 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; either version 2 of the License, or
(at your
> > + * option) any later version.
> > + *
> > + * 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
> > + */
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/init.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/irq.h>
> > +#include <linux/types.h>
> > +#include <linux/clocksource.h>
> > +#include <linux/clockchips.h>
> > +#include <linux/io.h>
> > +#include <asm/mach/time.h>
> > +#include <mach/hardware.h>
> > +
> > +/*
> > + * This driver configures the 2 16-bit count-up timers as follows:
> > + *
> > + * T1: Timer 1, clocksource for generic timekeeping
> > + * T2: Timer 2, clockevent source for hrtimers
> > + * T3: Timer 3, <unused>
> > + *
> > + * The input frequency to the timer module is 200MHz which is
common to all the
> > + * timer channel (T1, T2, and T3)
> > + * Clocksource timer resolution is 160ns
> > + * Clockevent timer resolution is 160ns
> > + */
> > +#define XTTCPSS_CLOCKSOURCE	0	/* Timer 1 as a generic
timekeeping */
> > +#define XTTCPSS_CLOCKEVENT	1	/* Timer 2 as a clock event */
> > +
> > +#define XTTCPSS_TIMER_BASE	TTC0_BASE
> > +
> > +/*
> > + * Timer Register Offset Definitions of Timer 1, Increment base
address by 4
> > + * and use same offsets for Timer 2
> > + */
> > +#define XTTCPSS_CLK_CNTRL_OFFSET	0x00 /* Clock Control Reg, RW */
> > +#define XTTCPSS_CNT_CNTRL_OFFSET	0x0C /* Counter Control Reg, RW
*/
> > +#define XTTCPSS_COUNT_VAL_OFFSET	0x18 /* Counter Value Reg, RO */
> > +#define XTTCPSS_INTR_VAL_OFFSET		0x24 /* Interval Count
Reg, RW */
> > +#define XTTCPSS_MATCH_1_OFFSET		0x30 /* Match 1 Value
Reg, RW */
> > +#define XTTCPSS_MATCH_2_OFFSET		0x3C /* Match 2 Value
Reg, RW */
> > +#define XTTCPSS_MATCH_3_OFFSET		0x48 /* Match 3 Value
Reg, RW */
> > +#define XTTCPSS_ISR_OFFSET		0x54 /* Interrupt Status Reg, RO
*/
> > +#define XTTCPSS_IER_OFFSET		0x60 /* Interrupt Enable Reg, RW
*/
> > +
> > +/*
> > + * Bit mask to enable/disable the timer
> > + */
> > +#define XTTCPSS_CNT_CNTRL_ENABLE_MASK	0xFFFFFFFE
> 
> I found this really confusing reading through the code, but that's
> probably just me!  Perhaps if this was called
> XTTCPSS_CNT_CNTRL_DISABLE_MASK and defined to 1 then that might be a
> little easier to follow.
> 

I'll take a look, maybe the name change would be clearer.

> > +
> > +/*
> > + * Definitions of the timer read/write macro
> > + */
> > +#define xttcpss_read(addr)	__raw_readl((void __iomem *)addr)
> > +#define xttcpss_write(addr, val) __raw_writel(val, (void __iomem
*)(addr))
> > +
> > +
> > +/**
> > + * struct xttcpss_timer - This definition defines local timer
structure
> > + *
> > + * @name:	Name of Timer
> > + * @base_addr:	Base address of timer
> > + * @timer_irq:	irqaction structure for the timer device
> > + * @mode:       only valid for an clock event, periodic or one-shot
> > + **/
> > +struct xttcpss_timer {
> > +	char *name;
> > +	unsigned long base_addr;
> 
> Shouldn't this really be a void __iomem pointer?  This could eliminate
> the need for xttcpss_write and xttcpss_read.

That would work too. I kind of like having the I/O accessors as I've
found them handy 
sometimes for debugging.  I'll check it out and consider it as maybe
it's simpler 
and clearer.

> 
> > +	struct irqaction timer_irq;
> > +	enum clock_event_mode mode;
> > +};
> > +
> > +
> > +static struct xttcpss_timer timers[];
> > +static struct clock_event_device xttcpss_clockevent;
> > +
> > +/*
> > + * xttcpss_timer_irqs - Timers IRQ number
> > + */
> > +static int xttcpss_timer_irqs[2] = {
> > +	IRQ_TIMERCOUNTER0,	/* Timer 1 IRQ number */
> > +	IRQ_TIMERCOUNTER0 + 1,	/* Timer 2 IRQ number */
> > +};
> > +
> > +/**
> > + * xttcpss_set_interval - Set the timer interval value
> > + *
> > + * @timer:	Pointer to the timer instance
> > + * @cycles:	Timer interval ticks
> > + **/
> > +static void xttcpss_set_interval(struct xttcpss_timer *timer,
> > +					unsigned long cycles)
> > +{
> > +	u32 ctrl_reg;
> > +
> > +	/* Disable the counter, set the counter value  and re-enable
counter */
> > +	ctrl_reg = xttcpss_read(timer->base_addr +
XTTCPSS_CNT_CNTRL_OFFSET);
> > +	ctrl_reg |= ~(XTTCPSS_CNT_CNTRL_ENABLE_MASK);
> > +	xttcpss_write(timer->base_addr + XTTCPSS_CNT_CNTRL_OFFSET,
> > ctrl_reg);
> > +
> > +	pr_debug("set_interval, name = %s, period = %08X\n",
> > +			timer->name, (unsigned int)cycles);
> > +
> > +	xttcpss_write(timer->base_addr + XTTCPSS_INTR_VAL_OFFSET,
cycles);
> > +
> > +	/* Reset the counter (0x10) so that it starts from 0, one-shot
> > +	   mode makes this needed for timing to be right. */
> > +	ctrl_reg &= XTTCPSS_CNT_CNTRL_ENABLE_MASK;
> > +	ctrl_reg |= 0x10;
> > +	xttcpss_write(timer->base_addr + XTTCPSS_CNT_CNTRL_OFFSET,
> > ctrl_reg);
> > +}
> > +
> > +/**
> > + * xttcpss_clock_source_interrupt - Clock source timer interrupt
handler
> > + *
> > + * @irq:	IRQ number of the Timer
> > + * @dev_id:	void pointer to the xttcpss_timer instance
> > + *
> > + * This will be called when 16-bit clock source counter wraps
> > + *
> > + * returns: Always IRQ_HANDLED - success
> > + **/
> > +static irqreturn_t xttcpss_clock_source_interrupt(int irq, void
*dev_id)
> > +{
> > +	struct xttcpss_timer *timer = dev_id;
> > +
> > +	/* Acknowledge the interrupt */
> > +	xttcpss_write(timer->base_addr + XTTCPSS_ISR_OFFSET,
> > +		xttcpss_read(timer->base_addr + XTTCPSS_ISR_OFFSET));
> > +
> > +	return IRQ_HANDLED;
> > +}
> > +
> > +/**
> > + * xttcpss_clock_event_interrupt - Clock event timer interrupt
handler
> > + *
> > + * @irq:	IRQ number of the Timer
> > + * @dev_id:	void pointer to the xttcpss_timer instance
> > + *
> > + * returns: Always IRQ_HANDLED - success
> > + **/
> > +static irqreturn_t xttcpss_clock_event_interrupt(int irq, void
*dev_id)
> > +{
> > +	struct clock_event_device *evt = &xttcpss_clockevent;
> > +	struct xttcpss_timer *timer = dev_id;
> > +	u32 ctrl_reg;
> > +
> > +	/* Acknowledge the interrupt and call event handler */
> > +	xttcpss_write(timer->base_addr + XTTCPSS_ISR_OFFSET,
> > +		xttcpss_read(timer->base_addr + XTTCPSS_ISR_OFFSET));
> > +
> > +	if (timer->mode == CLOCK_EVT_MODE_ONESHOT) {
> > +
> > +		/* Disable the counter as it would keep running. */
> > +		ctrl_reg = xttcpss_read(timer->base_addr +
> > +					XTTCPSS_CNT_CNTRL_OFFSET);
> > +		ctrl_reg |= ~(XTTCPSS_CNT_CNTRL_ENABLE_MASK);
> 
> The clock events framework should reprogram the next event so you
don't
> actually need to disable the timer here.  Once the event handler has
> been called the timer will be reenabled with a new period, and as
we're
> running with interrupts disabled here we don't need to stop the timer.
> 

What about if there's not another event to be started?

> > +		xttcpss_write(timer->base_addr +
XTTCPSS_CNT_CNTRL_OFFSET,
> > +				ctrl_reg);
> > +	}
> > +
> > +	evt->event_handler(evt);
> > +
> > +	return IRQ_HANDLED;
> > +}
> > +
> > +/*
> > + * struct xttcpss_timer timers - This definition defines local
timers
> > + */
> > +static struct xttcpss_timer timers[] = {
> > +	[XTTCPSS_CLOCKSOURCE] = {
> > +		.name = "xttcpss clocksource",
> > +		.timer_irq = {
> > +			.flags = IRQF_DISABLED | IRQF_TIMER,
> > +			.handler = xttcpss_clock_source_interrupt,
> > +		}
> > +	},
> > +	[XTTCPSS_CLOCKEVENT] = {
> > +		.name = "xttcpss clockevent",
> > +		.timer_irq = {
> > +			.flags = IRQF_DISABLED | IRQF_TIMER,
> > +			.handler = xttcpss_clock_event_interrupt,
> > +		}
> > +	},
> > +};
> > +
> > +
> > +/**
> > + * xttcpss_timer_hardware_init - Initialize the timer hardware
> > + *
> > + * Initialize the hardware, registers the timer interrupts, set the
clock source
> > + * timer interval and enable the clock source timer
> > + **/
> > +static void __init xttcpss_timer_hardware_init(void)
> > +{
> > +	int timer_id;
> > +	struct xttcpss_timer *timer;
> > +
> > +	for (timer_id = 0; timer_id < ARRAY_SIZE(timers); timer_id++) {
> > +		timer = &timers[timer_id];
> > +
> > +		if (!(timer->name))
> > +			continue;
> > +
> > +		timer->base_addr = XTTCPSS_TIMER_BASE + (4*timer_id);
> > +
> > +		/* Disable counter, Enable Interval mode, Count up
timer,
> > +		 * Disable Match mode, Internal Clock source select, set
> > +		 * prescalar to 32, and Enable the Interval interrupt */
> > +		xttcpss_write(timer->base_addr +
XTTCPSS_CNT_CNTRL_OFFSET,
> > +				0x23);
> > +		xttcpss_write(timer->base_addr +
XTTCPSS_CLK_CNTRL_OFFSET, 0x9);
> > +		xttcpss_write(timer->base_addr + XTTCPSS_IER_OFFSET,
0x1);
> > +
> > +		/* Setup IRQ */
> > +		timer->timer_irq.name = timer->name;
> > +		timer->timer_irq.dev_id = (void *)timer;
> > +		if (timer->timer_irq.handler != NULL) {
> > +			setup_irq(xttcpss_timer_irqs[timer_id],
> > +				&timer->timer_irq);
> > +		}
> > +		if (timer_id == XTTCPSS_CLOCKSOURCE)
> > +			xttcpss_set_interval(timer, ~0);
> > +	}
> > +}
> > +
> > +/**
> > + * xttcpss_read_cycles - Reads the timer counter register
> > + *
> > + * returns: Current timer counter register value
> > + **/
> > +static cycle_t xttcpss_read_cycles(struct clocksource *cs)
> > +{
> > +	struct xttcpss_timer *timer = &timers[XTTCPSS_CLOCKSOURCE];
> > +
> > +	return (cycle_t)xttcpss_read(timer->base_addr +
> > +				XTTCPSS_COUNT_VAL_OFFSET);
> > +}
> > +
> > +
> > +/*
> > + * Instantiate and initialize the clock source structure
> > + */
> > +static struct clocksource clocksource_xttcpss = {
> > +	.name		= "xttcpss_timer1",
> > +	.rating		= 200,			/* Reasonable clock
source */
> > +	.read		= xttcpss_read_cycles,
> > +	.mask		= CLOCKSOURCE_MASK(16),
> > +	.shift		= 0,			/* Initialized to zero
*/
> > +	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
> > +};
> > +
> > +
> > +/**
> > + * xttcpss_set_next_event - Sets the time interval for next event
> > + *
> > + * @cycles:	Timer interval ticks
> > + * @evt:	Address of clock event instance
> > + *
> > + * returns: Always 0 - success
> > + **/
> > +static int xttcpss_set_next_event(unsigned long cycles,
> > +					struct clock_event_device *evt)
> > +{
> > +	struct xttcpss_timer *timer = &timers[XTTCPSS_CLOCKEVENT];
> > +
> > +	xttcpss_set_interval(timer, cycles);
> > +	return 0;
> > +}
> > +
> > +/**
> > + * xttcpss_set_mode - Sets the mode of timer
> > + *
> > + * @mode:	Mode to be set
> > + * @evt:	Address of clock event instance
> > + **/
> > +static void xttcpss_set_mode(enum clock_event_mode mode,
> > +					struct clock_event_device *evt)
> > +{
> > +	struct xttcpss_timer *timer = &timers[XTTCPSS_CLOCKEVENT];
> > +	u32 ctrl_reg;
> > +
> > +	timer->mode = mode;
> > +
> > +	switch (mode) {
> > +	case CLOCK_EVT_MODE_PERIODIC:
> > +		xttcpss_set_interval(timer, CLOCK_TICK_RATE / HZ);
> > +		break;
> > +	case CLOCK_EVT_MODE_ONESHOT:
> > +	case CLOCK_EVT_MODE_UNUSED:
> > +	case CLOCK_EVT_MODE_SHUTDOWN:
> > +		ctrl_reg = xttcpss_read(timer->base_addr +
> > +					XTTCPSS_CNT_CNTRL_OFFSET);
> > +		ctrl_reg |= ~(XTTCPSS_CNT_CNTRL_ENABLE_MASK);
> > +		xttcpss_write(timer->base_addr +
XTTCPSS_CNT_CNTRL_OFFSET,
> > +				ctrl_reg);
> > +		break;
> > +	case CLOCK_EVT_MODE_RESUME:
> > +		ctrl_reg = xttcpss_read(timer->base_addr +
> > +					XTTCPSS_CNT_CNTRL_OFFSET);
> > +		ctrl_reg &= XTTCPSS_CNT_CNTRL_ENABLE_MASK;
> > +		xttcpss_write(timer->base_addr +
XTTCPSS_CNT_CNTRL_OFFSET,
> > +				ctrl_reg);
> > +		break;
> > +	}
> > +}
> > +
> > +/*
> > + * Instantiate and initialize the clock event structure
> > + */
> > +static struct clock_event_device xttcpss_clockevent = {
> > +	.name		= "xttcpss_timer2",
> > +	.features	= CLOCK_EVT_FEAT_PERIODIC |
CLOCK_EVT_FEAT_ONESHOT,
> > +	.shift		= 0,		/* Initialized to zero */
> > +	.set_next_event	= xttcpss_set_next_event,
> > +	.set_mode	= xttcpss_set_mode,
> > +	.rating		= 200,
> > +};
> > +
> > +/**
> > + * xttcpss_timer_init - Initialize the timer
> > + *
> > + * Initializes the timer hardware and registers the clock source
and clock event
> > + * timers with Linux kernal timer framework
> > + **/
> > +static void __init xttcpss_timer_init(void)
> > +{
> > +	u32 shift;
> > +	u64 temp;
> > +
> > +	xttcpss_timer_hardware_init();
> > +
> > +	/* Calculate the nanoseconds to cycles divisor value for clock
source
> > +	 * timer */
> > +	for (shift = 16; shift > 0; shift--) {
> > +		temp = (u64) NSEC_PER_SEC << shift;
> > +		do_div(temp, CLOCK_TICK_RATE);
> > +		if ((temp >> 32) == 0)
> > +			break;
> > +	}
> > +
> > +	/* Setup clocksource */
> > +	clocksource_xttcpss.shift = shift;
> > +	clocksource_xttcpss.mult =
> > +		clocksource_hz2mult(CLOCK_TICK_RATE,
clocksource_xttcpss.shift);
> > +
> > +	if (clocksource_register(&clocksource_xttcpss))
> > +		printk(KERN_ERR "xttcpss_timer_init: can't register
clocksource"
> > +				" for %s\n", clocksource_xttcpss.name);
> 
> If you use clocksource_register_hz() then you don't need to worry
about
> calculating shift and mult, the generic framework will do that for
you.
> 

Yes, sounds easier.

> > +	/* Calculate the nanoseconds to cycles divisor value for clock
event
> > +	 * timer */
> > +	for (shift = 16; shift > 0; shift--) {
> > +		temp = (u64) CLOCK_TICK_RATE << shift;
> > +		do_div(temp, NSEC_PER_SEC);
> > +		if ((temp >> 32) == 0)
> > +			break;
> > +	}
> > +
> > +	/* Setup clockevent */
> > +	xttcpss_clockevent.shift = shift;
> > +	xttcpss_clockevent.mult = div_sc(CLOCK_TICK_RATE, NSEC_PER_SEC,
> > +
xttcpss_clockevent.shift);
> 
> clockevents_calc_mult_shift()?
> 

Yep, Russell mentioned these type of changes also. Thanks a lot for the
review Jamie. 

I Will try to get changes incorporated into a V2 of the patches.

-- John

> > +
> > +	xttcpss_clockevent.max_delta_ns =
> > +		clockevent_delta2ns(0xfffe, &xttcpss_clockevent);
> > +	xttcpss_clockevent.min_delta_ns =
> > +		clockevent_delta2ns(1, &xttcpss_clockevent);
> > +
> > +	xttcpss_clockevent.cpumask = cpumask_of(0);
> > +	clockevents_register_device(&xttcpss_clockevent);
> > +}
> > +
> > +#ifdef CONFIG_PM
> > +/**
> > + * xttcpss_timer_suspend - Suspend the timer
> > + *
> > + * Disables all (clock source and clock event) the timers
> > + **/
> > +static void xttcpss_timer_suspend(void)
> > +{
> > +	struct xttcpss_timer *source_timer =
&timers[XTTCPSS_CLOCKSOURCE];
> > +	struct xttcpss_timer *event_timer = &timers[XTTCPSS_CLOCKEVENT];
> > +	u32 ctrl_reg;
> > +
> > +	/* Disable clocksource timer */
> > +	ctrl_reg = xttcpss_read(source_timer->base_addr +
> > +				XTTCPSS_CNT_CNTRL_OFFSET);
> > +	ctrl_reg |= ~(XTTCPSS_CNT_CNTRL_ENABLE_MASK);
> > +	xttcpss_write(source_timer->base_addr +
> > XTTCPSS_CNT_CNTRL_OFFSET,
> > +				ctrl_reg);
> > +
> > +	/* Disable clockevent timer */
> > +	ctrl_reg = xttcpss_read(event_timer->base_addr +
> > +				XTTCPSS_CNT_CNTRL_OFFSET);
> > +	ctrl_reg |= ~(XTTCPSS_CNT_CNTRL_ENABLE_MASK);
> > +	xttcpss_write(event_timer->base_addr + XTTCPSS_CNT_CNTRL_OFFSET,
> > +				ctrl_reg);
> > +}
> > +
> > +/**
> > + * xttcpss_timer_resume - Resume the timer
> > + *
> > + * Enables  all (clock source and clock event) the timers
> > + **/
> > +static void xttcpss_timer_resume(void)
> > +{
> > +	struct xttcpss_timer *source_timer =
&timers[XTTCPSS_CLOCKSOURCE];
> > +	struct xttcpss_timer *event_timer = &timers[XTTCPSS_CLOCKEVENT];
> > +	u32 ctrl_reg;
> > +
> > +	/* Enable clocksource timer */
> > +	ctrl_reg = xttcpss_read(source_timer->base_addr +
> > +				XTTCPSS_CNT_CNTRL_OFFSET);
> > +	ctrl_reg &= XTTCPSS_CNT_CNTRL_ENABLE_MASK;
> > +	xttcpss_write(source_timer->base_addr +
> > XTTCPSS_CNT_CNTRL_OFFSET,
> > +				ctrl_reg);
> > +
> > +	/* Enable clockevent timer */
> > +	ctrl_reg = xttcpss_read(event_timer->base_addr +
> > +				XTTCPSS_CNT_CNTRL_OFFSET);
> > +	ctrl_reg &= XTTCPSS_CNT_CNTRL_ENABLE_MASK;
> > +	xttcpss_write(event_timer->base_addr + XTTCPSS_CNT_CNTRL_OFFSET,
> > +				ctrl_reg);
> > +}
> > +#else
> > +#define xttcpss_timer_suspend NULL
> > +#define xttcpss_timer_resume NULL
> > +#endif
> > +
> > +/*
> > + * Instantiate and initialize the system timer structure
> > + */
> > +struct sys_timer xttcpss_sys_timer = {
> > +	.init		= xttcpss_timer_init,
> > +	.suspend	= xttcpss_timer_suspend,
> > +	.resume		= xttcpss_timer_resume,
> > +};
> > --
> > 1.6.2.1
> >
> >
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