Subject: [PATCH v2] ARM: ks8695: convert to generic time and clocksource

From: [email-masked] (Greg Ungerer)
Date: Mon, 3 Sep 2012 15:15:55 +1000

On 03/09/12 11:12, Greg Ungerer wrote:
> On 01/09/12 09:49, Linus Walleij wrote:
>> Old platforms using ancient gettimeoffset() and other arcane
>> APIs are standing in the way of cleaning up the ARM kernel.
>>
>> This is an attempt at blind-coding a generic time and clocksource
>> driver for the platform by way of a datasheet and looking at the
>> old code, it'd be great if someone who is actually using this
>> machine could test it.
>>
>> If noone volunteers to do this I will instead propose a patch
>> deleting the machine altogether.
>>
>> Signed-off-by: Linus Walleij <[email-masked]>
>> ---
>> ChangeLog v1->v2:
>> - Corrected the mask when setting clockevents from & TMCON_T1EN
>>    to & ~TMCON_T1EN so it doesn't shut down the clock source.
>
> Same result, still doesn't count time. If I have a few minutes today
> I'll see if I can debug any.

The timer interrupt itself seems to be coming at about the correct rate
(given CONFIG_HZ=100):

# cat /proc/interrupts
            CPU0
   7:      12036         -  ks8695_tick

[WAIT 10 seconds]

# cat /proc/interrupts
            CPU0
   7:      13032         -  ks8695_tick

Regards
Greg

>> ---
>>   arch/arm/Kconfig            |   3 +-
>>   arch/arm/mach-ks8695/time.c | 123 +++++++++++++++++++++++++++++++-------------
>>   2 files changed, 88 insertions(+), 38 deletions(-)
>>
>> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>> index 6d6e18f..e9ce038 100644
>> --- a/arch/arm/Kconfig
>> +++ b/arch/arm/Kconfig
>> @@ -652,8 +652,9 @@ config ARCH_KS8695
>>       bool "Micrel/Kendin KS8695"
>>       select CPU_ARM922T
>>       select ARCH_REQUIRE_GPIOLIB
>> -    select ARCH_USES_GETTIMEOFFSET
>>       select NEED_MACH_MEMORY_H
>> +    select CLKSRC_MMIO
>> +    select GENERIC_CLOCKEVENTS
>>       help
>>         Support for Micrel/Kendin KS8695 "Centaur" (ARM922T) based
>>         System-on-Chip devices.
>> diff --git a/arch/arm/mach-ks8695/time.c b/arch/arm/mach-ks8695/time.c
>> index 6974c23..1ba0182 100644
>> --- a/arch/arm/mach-ks8695/time.c
>> +++ b/arch/arm/mach-ks8695/time.c
>> @@ -25,6 +25,8 @@
>>   #include <linux/kernel.h>
>>   #include <linux/sched.h>
>>   #include <linux/io.h>
>> +#include <linux/clockchips.h>
>> +#include <linux/clocksource.h>
>>
>>   #include <asm/mach/time.h>
>>   #include <asm/system_misc.h>
>> @@ -53,44 +55,68 @@
>>   /* Timer0 Timeout Counter Register */
>>   #define T0TC_WATCHDOG        (0xff)        /* Enable watchdog mode */
>>
>> -/*
>> - * Returns number of ms since last clock interrupt.  Note that interrupts
>> - * will have been disabled by do_gettimeoffset()
>> - */
>> -static unsigned long ks8695_gettimeoffset (void)
>> +static void ks8695_set_mode(enum clock_event_mode mode,
>> +                struct clock_event_device *evt)
>>   {
>> -    unsigned long elapsed, tick2, intpending;
>> +    if (mode == CLOCK_EVT_FEAT_PERIODIC) {
>> +        u32 rate = DIV_ROUND_CLOSEST(KS8695_CLOCK_RATE, HZ);
>> +        u32 half = DIV_ROUND_CLOSEST(rate, 2);
>> +        u32 tmcon;
>> +
>> +        /* Disable timer 1 */
>> +        tmcon = readl_relaxed(KS8695_TMR_VA + KS8695_TMCON);
>> +        tmcon &= ~TMCON_T1EN;
>> +        writel_relaxed(tmcon, KS8695_TMR_VA + KS8695_TMCON);
>> +
>> +        /* Both registers need to count down */
>> +        writel_relaxed(half, KS8695_TMR_VA + KS8695_T1TC);
>> +        writel_relaxed(half, KS8695_TMR_VA + KS8695_T1PD);
>> +
>> +        /* Re-enable timer1 */
>> +        tmcon |= TMCON_T1EN;
>> +        writel_relaxed(tmcon, KS8695_TMR_VA + KS8695_TMCON);
>> +    }
>> +}
>>
>> -    /*
>> -     * Get the current number of ticks.  Note that there is a race
>> -     * condition between us reading the timer and checking for an
>> -     * interrupt.  We solve this by ensuring that the counter has not
>> -     * reloaded between our two reads.
>> -     */
>> -    elapsed = readl_relaxed(KS8695_TMR_VA + KS8695_T1TC) + readl_relaxed(KS8695_TMR_VA + KS8695_T1PD);
>> -    do {
>> -        tick2 = elapsed;
>> -        intpending = readl_relaxed(KS8695_IRQ_VA + KS8695_INTST) & (1 << KS8695_IRQ_TIMER1);
>> -        elapsed = readl_relaxed(KS8695_TMR_VA + KS8695_T1TC) + readl_relaxed(KS8695_TMR_VA + KS8695_T1PD);
>> -    } while (elapsed > tick2);
>> -
>> -    /* Convert to number of ticks expired (not remaining) */
>> -    elapsed = (CLOCK_TICK_RATE / HZ) - elapsed;
>> -
>> -    /* Is interrupt pending?  If so, then timer has been reloaded already. */
>> -    if (intpending)
>> -        elapsed += (CLOCK_TICK_RATE / HZ);
>> -
>> -    /* Convert ticks to usecs */
>> -    return (unsigned long)(elapsed * (tick_nsec / 1000)) / LATCH;
>> +static int ks8695_set_next_event(unsigned long cycles,
>> +                 struct clock_event_device *evt)
>> +
>> +{
>> +    u32 half = DIV_ROUND_CLOSEST(cycles, 2);
>> +    u32 tmcon;
>> +
>> +    /* Disable timer 1 */
>> +    tmcon = readl_relaxed(KS8695_TMR_VA + KS8695_TMCON);
>> +    tmcon &= ~TMCON_T1EN;
>> +    writel_relaxed(tmcon, KS8695_TMR_VA + KS8695_TMCON);
>> +
>> +    /* Both registers need to count down */
>> +    writel_relaxed(half, KS8695_TMR_VA + KS8695_T1TC);
>> +    writel_relaxed(half, KS8695_TMR_VA + KS8695_T1PD);
>> +
>> +    /* Re-enable timer1 */
>> +    tmcon |= TMCON_T1EN;
>> +    writel_relaxed(tmcon, KS8695_TMR_VA + KS8695_TMCON);
>> +
>> +    return 0;
>>   }
>>
>> +static struct clock_event_device clockevent_ks8695 = {
>> +    .name        = "ks8695_t1tc",
>> +    .rating        = 300, /* Reasonably fast and accurate clock event */
>> +    .features    = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_PERIODIC,
>> +    .set_next_event    = ks8695_set_next_event,
>> +    .set_mode    = ks8695_set_mode,
>> +};
>> +
>>   /*
>>    * IRQ handler for the timer.
>>    */
>>   static irqreturn_t ks8695_timer_interrupt(int irq, void *dev_id)
>>   {
>> -    timer_tick();
>> +    struct clock_event_device *evt = &clockevent_ks8695;
>> +
>> +    evt->event_handler(evt);
>>       return IRQ_HANDLED;
>>   }
>>
>> @@ -102,18 +128,42 @@ static struct irqaction ks8695_timer_irq = {
>>
>>   static void ks8695_timer_setup(void)
>>   {
>> -    unsigned long tmout = CLOCK_TICK_RATE / HZ;
>>       unsigned long tmcon;
>>
>> -    /* disable timer1 */
>> +    /* Disable timer 0 and 1 */
>>       tmcon = readl_relaxed(KS8695_TMR_VA + KS8695_TMCON);
>> -    writel_relaxed(tmcon & ~TMCON_T1EN, KS8695_TMR_VA + KS8695_TMCON);
>> +    tmcon &= ~TMCON_T0EN;
>> +    tmcon &= ~TMCON_T1EN;
>> +    writel_relaxed(tmcon, KS8695_TMR_VA + KS8695_TMCON);
>>
>> -    writel_relaxed(tmout / 2, KS8695_TMR_VA + KS8695_T1TC);
>> -    writel_relaxed(tmout / 2, KS8695_TMR_VA + KS8695_T1PD);
>> +    /*
>> +     * Set up timer 0 to loop indefinately, count 32 bits with TOUT0
>> +     * set to zero, then 1 bit with TOUT0 set to 1. The reason we are doing
>> +     * this is that it's not allowed to set either register to 0, then the
>> +     * behaviour is "unpredictable". This injects a faulty pulse every
>> +     * 2^32-1 cycles but we can surely live with that rather than
>> +     * complicating the code.
>> +     */
>> +    writel_relaxed(0xFFFFFFFFU, KS8695_TMR_VA + KS8695_T0TC);
>> +    writel_relaxed(1, KS8695_TMR_VA + KS8695_T0PD);
>> +    /* Start timer 0 */
>> +    tmcon |= TMCON_T0EN;
>> +    writel_relaxed(tmcon, KS8695_TMR_VA + KS8695_TMCON);
>> +    /* Use timer 0 as clocksource */
>> +    if (clocksource_mmio_init((void *) KS8695_TMR_VA + KS8695_T0TC,
>> +            "ks8695_t0tc", KS8695_CLOCK_RATE, 300, 32,
>> +            clocksource_mmio_readl_up))
>> +        pr_err("timer: failed to initialize KS8695 clock source\n");
>>
>> -    /* re-enable timer1 */
>> -    writel_relaxed(tmcon | TMCON_T1EN, KS8695_TMR_VA + KS8695_TMCON);
>> +    /*
>> +     * Use timer 1 to fire IRQs on the timeline, only support one-shot
>> +     * mode and the system will take care of the rest. Minimum 2 cycles
>> +     * (one on each counter) maximum 2*2^32, but the API will only
>> +     * accept up to a 32bit full word (0xFFFFFFFFU).
>> +     */
>> +    clockevents_config_and_register(&clockevent_ks8695,
>> +                    KS8695_CLOCK_RATE, 2,
>> +                    0xFFFFFFFFU);
>>   }
>>
>>   static void __init ks8695_timer_init (void)
>> @@ -126,7 +176,6 @@ static void __init ks8695_timer_init (void)
>>
>>   struct sys_timer ks8695_timer = {
>>       .init        = ks8695_timer_init,
>> -    .offset        = ks8695_gettimeoffset,
>>   };
>>
>>   void ks8695_restart(char mode, const char *cmd)
>>
>
>

-- 
------------------------------------------------------------------------
Greg Ungerer  --  Principal Engineer        EMAIL:     gerg at snapgear.com
SnapGear Group, McAfee                      PHONE:       +61 7 3435 2888
8 Gardner Close                             FAX:         +61 7 3217 5323
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