Re: [PATCH 2/2] rtc: tegra: Implement suspend clock source

[Dmitry Osipenko <digetx@gmail.com>]

14.06.2019 13:47, Thierry Reding пишет:
> From: Thierry Reding <treding@nvidia.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@nvidia.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.