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ARM: tegra: use us counter as delay timer

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Tegra has a micro-second counter whose rate doesn't vary with cpufreq
 changes. Register it so it can be used as the delay timer, so delays
 aren't influenced by cpufreq.
 
 I've made this a separate branch since it touches a few files outside
 arch/arm/mach-tegra/. This can be merged anywhere that conflicts need
 to be resolved, although I know of no such places at present.
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Merge tag 'tegra-for-3.17-delay-timer' of git://git.kernel.org/pub/scm/linux/kernel/git/tegra/linux into next/soc

Merge "ARM: tegra: use us counter as delay timer" from Stephen Warren:

Tegra has a micro-second counter whose rate doesn't vary with cpufreq
changes. Register it so it can be used as the delay timer, so delays
aren't influenced by cpufreq.

* tag 'tegra-for-3.17-delay-timer' of git://git.kernel.org/pub/scm/linux/kernel/git/tegra/linux:
  clocksource: tegra: Use us counter as delay timer
  ARM: choose highest resolution delay timer
  kernel: add calibration_delay_done()

Signed-off-by: Olof Johansson <olof@lixom.net>
This commit is contained in:
Olof Johansson 2014-07-06 17:47:28 -07:00
commit b040614c5b
3 changed files with 46 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

26
arch/arm/lib/delay.c
View file

@ -19,6 +19,7 @@
* Author: Will Deacon <will.deacon@arm.com>
*/
#include <linux/clocksource.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/kernel.h>
@ -36,6 +37,7 @@ struct arm_delay_ops arm_delay_ops = {
static const struct delay_timer *delay_timer;
static bool delay_calibrated;
static u64 delay_res;
int read_current_timer(unsigned long *timer_val)
{
@ -47,6 +49,11 @@ int read_current_timer(unsigned long *timer_val)
}
EXPORT_SYMBOL_GPL(read_current_timer);
static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
{
return (cyc * mult) >> shift;
}
static void __timer_delay(unsigned long cycles)
{
cycles_t start = get_cycles();
@ -69,18 +76,24 @@ static void __timer_udelay(unsigned long usecs)
void __init register_current_timer_delay(const struct delay_timer *timer)
{
if (!delay_calibrated) {
pr_info("Switching to timer-based delay loop\n");
u32 new_mult, new_shift;
u64 res;
clocks_calc_mult_shift(&new_mult, &new_shift, timer->freq,
NSEC_PER_SEC, 3600);
res = cyc_to_ns(1ULL, new_mult, new_shift);
if (!delay_calibrated && (!delay_res || (res < delay_res))) {
pr_info("Switching to timer-based delay loop, resolution %lluns\n", res);
delay_timer = timer;
lpj_fine = timer->freq / HZ;
delay_res = res;
/* cpufreq may scale loops_per_jiffy, so keep a private copy */
arm_delay_ops.ticks_per_jiffy = lpj_fine;
arm_delay_ops.delay = __timer_delay;
arm_delay_ops.const_udelay = __timer_const_udelay;
arm_delay_ops.udelay = __timer_udelay;
delay_calibrated = true;
} else {
pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");
}
@ -91,3 +104,8 @@ unsigned long calibrate_delay_is_known(void)
delay_calibrated = true;
return lpj_fine;
}
void calibration_delay_done(void)
{
delay_calibrated = true;
}

13
drivers/clocksource/tegra20_timer.c
View file

@ -27,6 +27,7 @@
#include <linux/of_address.h>
#include <linux/of_irq.h>
#include <linux/sched_clock.h>
#include <linux/delay.h>
#include <asm/mach/time.h>
#include <asm/smp_twd.h>
@ -53,6 +54,8 @@ static void __iomem *rtc_base;
static struct timespec persistent_ts;
static u64 persistent_ms, last_persistent_ms;
static struct delay_timer tegra_delay_timer;
#define timer_writel(value, reg) \
__raw_writel(value, timer_reg_base + (reg))
#define timer_readl(reg) \
@ -139,6 +142,11 @@ static void tegra_read_persistent_clock(struct timespec *ts)
*ts = *tsp;
}
static unsigned long tegra_delay_timer_read_counter_long(void)
{
return readl(timer_reg_base + TIMERUS_CNTR_1US);
}
static irqreturn_t tegra_timer_interrupt(int irq, void *dev_id)
{
struct clock_event_device *evt = (struct clock_event_device *)dev_id;
@ -206,6 +214,11 @@ static void __init tegra20_init_timer(struct device_node *np)
BUG();
}
tegra_delay_timer.read_current_timer =
tegra_delay_timer_read_counter_long;
tegra_delay_timer.freq = 1000000;
register_current_timer_delay(&tegra_delay_timer);
ret = setup_irq(tegra_timer_irq.irq, &tegra_timer_irq);
if (ret) {
pr_err("Failed to register timer IRQ: %d\n", ret);

11
init/calibrate.c
View file

@ -262,6 +262,15 @@ unsigned long __attribute__((weak)) calibrate_delay_is_known(void)
return 0;
}
/*
* Indicate the cpu delay calibration is done. This can be used by
* architectures to stop accepting delay timer registrations after this point.
*/
void __attribute__((weak)) calibration_delay_done(void)
{
}
void calibrate_delay(void)
{
unsigned long lpj;
@ -301,4 +310,6 @@ void calibrate_delay(void)
loops_per_jiffy = lpj;
printed = true;
calibration_delay_done();
}