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Date:   Fri, 14 Jun 2019 15:41:10 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] rtc: tegra: Implement suspend clock source

On Fri, Jun 14, 2019 at 03:01:13PM +0300, Dmitry Osipenko wrote:
> 14.06.2019 13:47, Thierry Reding пишет:
> > From: Thierry Reding <treding@...dia.com>
> > 
> > The suspend clock source for Tegra210 and earlier is currently
> > implemented in the Tegra timer driver. However, the suspend clock source
> > code accesses registers that are part of the RTC hardware block, so both
> > can step on each others' toes. In practice this isn't an issue, but
> > there is no reason why the RTC driver can't implement the clock source,
> > so move the code over to the tegra-rtc driver.
> > 
> > Signed-off-by: Thierry Reding <treding@...dia.com>
> > ---
> >  drivers/clocksource/timer-tegra.c | 44 -------------------------------
> >  drivers/rtc/rtc-tegra.c           | 42 +++++++++++++++++++++++++++++
> >  2 files changed, 42 insertions(+), 44 deletions(-)
> > 
> > diff --git a/drivers/clocksource/timer-tegra.c b/drivers/clocksource/timer-tegra.c
> > index e6608141cccb..87eac618924d 100644
> > --- a/drivers/clocksource/timer-tegra.c
> > +++ b/drivers/clocksource/timer-tegra.c
> > @@ -21,10 +21,6 @@
> >  
> >  #include "timer-of.h"
> >  
> > -#define RTC_SECONDS		0x08
> > -#define RTC_SHADOW_SECONDS	0x0c
> > -#define RTC_MILLISECONDS	0x10
> > -
> >  #define TIMERUS_CNTR_1US	0x10
> >  #define TIMERUS_USEC_CFG	0x14
> >  #define TIMERUS_CNTR_FREEZE	0x4c
> > @@ -164,34 +160,6 @@ static struct delay_timer tegra_delay_timer = {
> >  };
> >  #endif
> >  
> > -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 function 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(struct clocksource *cs)
> > -{
> > -	void __iomem *reg_base = timer_of_base(&suspend_rtc_to);
> > -
> > -	u32 ms = readl_relaxed(reg_base + RTC_MILLISECONDS);
> > -	u32 s = readl_relaxed(reg_base + RTC_SHADOW_SECONDS);
> > -
> > -	return (u64)s * MSEC_PER_SEC + ms;
> > -}
> > -
> > -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,
> > -};
> > -
> >  static inline unsigned int tegra_base_for_cpu(int cpu, bool tegra20)
> >  {
> >  	if (tegra20) {
> > @@ -385,15 +353,3 @@ static int __init tegra20_init_timer(struct device_node *np)
> >  	return tegra_init_timer(np, true, rating);
> >  }
> >  TIMER_OF_DECLARE(tegra20_timer, "nvidia,tegra20-timer", tegra20_init_timer);
> > -
> > -static int __init tegra20_init_rtc(struct device_node *np)
> > -{
> > -	int ret;
> > -
> > -	ret = timer_of_init(np, &suspend_rtc_to);
> > -	if (ret)
> > -		return ret;
> > -
> > -	return clocksource_register_hz(&suspend_rtc_clocksource, 1000);
> > -}
> > -TIMER_OF_DECLARE(tegra20_rtc, "nvidia,tegra20-rtc", tegra20_init_rtc);
> > diff --git a/drivers/rtc/rtc-tegra.c b/drivers/rtc/rtc-tegra.c
> > index 8fa1b3febf69..6da54264a27a 100644
> > --- a/drivers/rtc/rtc-tegra.c
> > +++ b/drivers/rtc/rtc-tegra.c
> > @@ -6,6 +6,7 @@
> >   */
> >  
> >  #include <linux/clk.h>
> > +#include <linux/clocksource.h>
> >  #include <linux/delay.h>
> >  #include <linux/init.h>
> >  #include <linux/io.h>
> > @@ -52,8 +53,15 @@ struct tegra_rtc_info {
> >  	struct clk *clk;
> >  	int irq; /* alarm and periodic IRQ */
> >  	spinlock_t lock;
> > +
> > +	struct clocksource clksrc;
> >  };
> >  
> > +static struct tegra_rtc_info *to_tegra_rtc(struct clocksource *clksrc)
> > +{
> > +	return container_of(clksrc, struct tegra_rtc_info, clksrc);
> > +}
> > +
> >  /*
> >   * RTC hardware is busy when it is updating its values over AHB once every
> >   * eight 32 kHz clocks (~250 us). Outside of these updates the CPU is free to
> > @@ -268,6 +276,17 @@ static const struct rtc_class_ops tegra_rtc_ops = {
> >  	.alarm_irq_enable = tegra_rtc_alarm_irq_enable,
> >  };
> >  
> > +static u64 tegra_rtc_read_ms(struct clocksource *clksrc)
> > +{
> > +	struct tegra_rtc_info *info = to_tegra_rtc(clksrc);
> > +	u32 ms, s;
> > +
> > +	ms = readl_relaxed(info->base + TEGRA_RTC_REG_MILLI_SECONDS);
> > +	s = readl_relaxed(info->base + TEGRA_RTC_REG_SHADOW_SECONDS);
> > +
> > +	return (u64)s * MSEC_PER_SEC + ms;
> > +}
> > +
> >  static const struct of_device_id tegra_rtc_dt_match[] = {
> >  	{ .compatible = "nvidia,tegra20-rtc", },
> >  	{}
> > @@ -339,6 +358,28 @@ static int tegra_rtc_probe(struct platform_device *pdev)
> >  		goto disable_clk;
> >  	}
> >  
> > +	/*
> > +	 * The Tegra RTC is the only reliable clock source that persists
> > +	 * across an SC7 transition (VDD_CPU and VDD_CORE off) on Tegra210
> > +	 * and earlier. Starting with Tegra186, the ARM v8 architected timer
> > +	 * is in an always on power partition and its reference clock keeps
> > +	 * running during SC7. Therefore, we technically don't need to have
> > +	 * the RTC register as a clock source on Tegra186 and later, but it
> > +	 * doesn't hurt either, so we just register it unconditionally here.
> > +	 */
> > +	info->clksrc.name = "tegra_rtc";
> > +	info->clksrc.rating = 200;
> > +	info->clksrc.read = tegra_rtc_read_ms;
> > +	info->clksrc.mask = CLOCKSOURCE_MASK(32);
> 
> Hm.. shouldn't this be CLOCKSOURCE_MASK(52)? Given that there are 32 bits for seconds and
> 10bits for milliseconds.

Did you mean to say CLOCKSOURCE_MASK(42)? Yeah, that's probably better
here.

Thierry

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