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Date:   Tue, 2 Apr 2019 18:49:51 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Joseph Lo <josephl@...dia.com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-kernel@...r.kernel.org,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] clocksource/drivers/tegra: rework for compensation of
 suspend time

On Tue, Apr 02, 2019 at 11:50:20PM +0800, Joseph Lo wrote:
> On 4/2/19 10:46 PM, Thierry Reding wrote:
> > On Tue, Apr 02, 2019 at 11:02:34AM +0800, Joseph Lo wrote:
> > > Since the clocksource framework has the support for suspend time
> > > compensation. Re-work the driver to use that, so we can reduce the
> > > duplicate code.
> > > 
> > > Suggested-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> > > Signed-off-by: Joseph Lo <josephl@...dia.com>
> > > ---
> > >   drivers/clocksource/timer-tegra20.c | 63 +++++++++--------------------
> > >   1 file changed, 20 insertions(+), 43 deletions(-)
> > 
> > Nice!
> > 
> > > 
> > > diff --git a/drivers/clocksource/timer-tegra20.c b/drivers/clocksource/timer-tegra20.c
> > > index fdb3d795a409..919b3568c495 100644
> > > --- a/drivers/clocksource/timer-tegra20.c
> > > +++ b/drivers/clocksource/timer-tegra20.c
> > > @@ -60,9 +60,6 @@
> > >   static u32 usec_config;
> > >   static void __iomem *timer_reg_base;
> > >   #ifdef CONFIG_ARM
> > > -static void __iomem *rtc_base;
> > > -static struct timespec64 persistent_ts;
> > > -static u64 persistent_ms, last_persistent_ms;
> > >   static struct delay_timer tegra_delay_timer;
> > >   #endif
> > > @@ -199,40 +196,30 @@ static unsigned long tegra_delay_timer_read_counter_long(void)
> > >   	return readl(timer_reg_base + TIMERUS_CNTR_1US);
> > >   }
> > > +static struct timer_of suspend_rtc_to = {
> > > +	.flags = TIMER_OF_BASE | TIMER_OF_CLOCK,
> > > +};
> > > +
> > >   /*
> > >    * tegra_rtc_read - Reads the Tegra RTC registers
> > >    * Care must be taken that this funciton is not called while the
> > >    * tegra_rtc driver could be executing to avoid race conditions
> > >    * on the RTC shadow register
> > >    */
> > > -static u64 tegra_rtc_read_ms(void)
> > > +static u64 tegra_rtc_read_ms(struct clocksource *cs)
> > >   {
> > > -	u32 ms = readl(rtc_base + RTC_MILLISECONDS);
> > > -	u32 s = readl(rtc_base + RTC_SHADOW_SECONDS);
> > > +	u32 ms = readl(timer_of_base(&suspend_rtc_to) + RTC_MILLISECONDS);
> > > +	u32 s = readl(timer_of_base(&suspend_rtc_to) + RTC_SHADOW_SECONDS);
> > >   	return (u64)s * MSEC_PER_SEC + ms;
> > >   }
> > > -/*
> > > - * tegra_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.
> > > - * Care must be taken that this funciton is not called while the
> > > - * tegra_rtc driver could be executing to avoid race conditions
> > > - * on the RTC shadow register
> > > - */
> > > -static void tegra_read_persistent_clock64(struct timespec64 *ts)
> > > -{
> > > -	u64 delta;
> > > -
> > > -	last_persistent_ms = persistent_ms;
> > > -	persistent_ms = tegra_rtc_read_ms();
> > > -	delta = persistent_ms - last_persistent_ms;
> > > -
> > > -	timespec64_add_ns(&persistent_ts, delta * NSEC_PER_MSEC);
> > > -	*ts = persistent_ts;
> > > -}
> > > +static struct clocksource suspend_rtc_clocksource = {
> > > +	.name	= "tegra_suspend_timer",
> > > +	.rating	= 200,
> > > +	.read	= tegra_rtc_read_ms,
> > > +	.mask	= CLOCKSOURCE_MASK(32),
> > > +	.flags	= CLOCK_SOURCE_IS_CONTINUOUS | CLOCK_SOURCE_SUSPEND_NONSTOP,
> > > +};
> > >   #endif
> > >   static int tegra_timer_common_init(struct device_node *np, struct timer_of *to)
> > > @@ -385,25 +372,15 @@ static int __init tegra_init_timer(struct device_node *np)
> > >   static int __init tegra20_init_rtc(struct device_node *np)
> > >   {
> > > -	struct clk *clk;
> > > +	int ret;
> > > -	rtc_base = of_iomap(np, 0);
> > > -	if (!rtc_base) {
> > > -		pr_err("Can't map RTC registers\n");
> > > -		return -ENXIO;
> > > -	}
> > > +	ret = timer_of_init(np, &suspend_rtc_to);
> > > +	if (ret)
> > > +		return ret;
> > > -	/*
> > > -	 * rtc registers are used by read_persistent_clock, keep the rtc clock
> > > -	 * enabled
> > > -	 */
> > > -	clk = of_clk_get(np, 0);
> > > -	if (IS_ERR(clk))
> > > -		pr_warn("Unable to get rtc-tegra clock\n");
> > > -	else
> > > -		clk_prepare_enable(clk);
> > > +	clocksource_register_hz(&suspend_rtc_clocksource, 1000);
> > > -	return register_persistent_clock(tegra_read_persistent_clock64);
> > > +	return 0;
> > >   }
> > >   TIMER_OF_DECLARE(tegra20_rtc, "nvidia,tegra20-rtc", tegra20_init_rtc);
> > >   #endif
> > 
> > I wonder if there's any reason left for the #ifdefs now. My recollection
> > is that these were only needed because register_persistent_clock() was
> > not available on 64-bit ARM. The new APIs seem to be available
> > regardless of architecture, so do we still need to differentiate?
> > 
> 
> Actually, only Tegra20/30 that doesn't have ARM arch timer support need
> this. The latter Tegra chips which have ARM arch timer support use TSC (
> time stamp counter or timer system counter depends on the chip it has
> different name) as the timer source in the PMC. And it uses OSC during
> runtime and switches to 32KHz always-on clock source to keep counting when
> the chip is in the SC7 or LP0 state.
> 
> So I didn't change that for this reason.

Okay, looks good then.

Acked-by: Thierry Reding <treding@...dia.com>

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