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Date:   Fri, 14 Jun 2019 16:49:44 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...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

14.06.2019 16:41, Thierry Reding пишет:
> 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.

Yes, 42 :)

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