Re: [PATCH v4 3/3] clocksource: Add Low Power STM32 timers driver

[Daniel Lezcano <daniel.lezcano@linaro.org>]

On 17/02/2020 14:45, Benjamin Gaignard wrote:
> From: Benjamin Gaignard <benjamin.gaignard@linaro.org>
> 
> Implement clock event driver using low power STM32 timers.
> Low power timer counters running even when CPUs are stopped.
> It could be used as clock event broadcaster to wake up CPUs but not like
> a clocksource because each it rise an interrupt the counter restart from 0.
> 
> Low power timers have a 16 bits counter and a prescaler which allow to
> divide the clock per power of 2 to up 128 to target a 32KHz rate.
> 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
> Signed-off-by: Pascal Paillet <p.paillet@st.com>
> ---
> version 4:
> - move defines in mfd/stm32-lptimer.h
> - change compatiblename
> - reword commit message
> - make driver Kconfig depends of MFD_STM32_LPTIMER
> - remove useless include
> - remove rate and clk fields from the private structure
> - to add comments about the registers sequence in stm32_clkevent_lp_set_timer
> - rework probe function and use devm_request_irq()
> - do not allow module to be removed
> - make sure that wakeup interrupt is set
> 
>  drivers/clocksource/Kconfig          |   7 ++
>  drivers/clocksource/Makefile         |   1 +
>  drivers/clocksource/timer-stm32-lp.c | 213 +++++++++++++++++++++++++++++++++++
>  3 files changed, 221 insertions(+)
>  create mode 100644 drivers/clocksource/timer-stm32-lp.c
> 
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index cc909e465823..9fc2b513db6f 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -292,6 +292,13 @@ config CLKSRC_STM32
>  	select CLKSRC_MMIO
>  	select TIMER_OF
>  
> +config CLKSRC_STM32_LP
> +	bool "Low power clocksource for STM32 SoCs"
> +	depends on MFD_STM32_LPTIMER || COMPILE_TEST
> +	help
> +	  This option enables support for STM32 low power clockevent available
> +	  on STM32 SoCs
> +
>  config CLKSRC_MPS2
>  	bool "Clocksource for MPS2 SoCs" if COMPILE_TEST
>  	depends on GENERIC_SCHED_CLOCK
> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> index 713686faa549..c00fffbd4769 100644
> --- a/drivers/clocksource/Makefile
> +++ b/drivers/clocksource/Makefile
> @@ -44,6 +44,7 @@ obj-$(CONFIG_BCM_KONA_TIMER)	+= bcm_kona_timer.o
>  obj-$(CONFIG_CADENCE_TTC_TIMER)	+= timer-cadence-ttc.o
>  obj-$(CONFIG_CLKSRC_EFM32)	+= timer-efm32.o
>  obj-$(CONFIG_CLKSRC_STM32)	+= timer-stm32.o
> +obj-$(CONFIG_CLKSRC_STM32_LP)	+= timer-stm32-lp.o
>  obj-$(CONFIG_CLKSRC_EXYNOS_MCT)	+= exynos_mct.o
>  obj-$(CONFIG_CLKSRC_LPC32XX)	+= timer-lpc32xx.o
>  obj-$(CONFIG_CLKSRC_MPS2)	+= mps2-timer.o
> diff --git a/drivers/clocksource/timer-stm32-lp.c b/drivers/clocksource/timer-stm32-lp.c
> new file mode 100644
> index 000000000000..50eecdb88216
> --- /dev/null
> +++ b/drivers/clocksource/timer-stm32-lp.c
> @@ -0,0 +1,213 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) STMicroelectronics 2019 - All Rights Reserved
> + * Authors: Benjamin Gaignard <benjamin.gaignard@st.com> for STMicroelectronics.
> + *	    Pascal Paillet <p.paillet@st.com> for STMicroelectronics.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/clockchips.h>
> +#include <linux/interrupt.h>
> +#include <linux/mfd/stm32-lptimer.h>
> +#include <linux/module.h>
> +#include <linux/of_address.h>
> +#include <linux/of_irq.h>
> +#include <linux/platform_device.h>
> +#include <linux/pm_wakeirq.h>
> +
> +#define CFGR_PSC_OFFSET		9
> +#define STM32_LP_RATING		400
> +#define STM32_TARGET_CLKRATE	(32000 * HZ)
> +#define STM32_LP_MAX_PSC	7
> +
> +struct stm32_lp_private {
> +	struct regmap *reg;
> +	struct clock_event_device clkevt;
> +	unsigned long period;
> +};
> +
> +static struct stm32_lp_private*
> +to_priv(struct clock_event_device *clkevt)
> +{
> +	return container_of(clkevt, struct stm32_lp_private, clkevt);
> +}
> +
> +static int stm32_clkevent_lp_shutdown(struct clock_event_device *clkevt)
> +{
> +	struct stm32_lp_private *priv = to_priv(clkevt);
> +
> +	regmap_write(priv->reg, STM32_LPTIM_CR, 0);
> +	regmap_write(priv->reg, STM32_LPTIM_IER, 0);
> +	/* clear pending flags */
> +	regmap_write(priv->reg, STM32_LPTIM_ICR, STM32_LPTIM_ARRMCF);
> +
> +	return 0;
> +}
> +
> +static int stm32_clkevent_lp_set_timer(unsigned long evt,
> +				       struct clock_event_device *clkevt,
> +				       int is_periodic)
> +{
> +	struct stm32_lp_private *priv = to_priv(clkevt);
> +
> +	/* disable LPTIMER to be able to write into IER register*/
> +	regmap_write(priv->reg, STM32_LPTIM_CR, 0);
> +	/* enable ARR interrupt */
> +	regmap_write(priv->reg, STM32_LPTIM_IER, STM32_LPTIM_ARRMIE);
> +	/* enable LPTIMER to be able to write into ARR register */
> +	regmap_write(priv->reg, STM32_LPTIM_CR, STM32_LPTIM_ENABLE);
> +	/* set next event counter */
> +	regmap_write(priv->reg, STM32_LPTIM_ARR, evt);
> +
> +	/* start counter */
> +	if (is_periodic)
> +		regmap_write(priv->reg, STM32_LPTIM_CR,
> +			     STM32_LPTIM_CNTSTRT | STM32_LPTIM_ENABLE);
> +	else
> +		regmap_write(priv->reg, STM32_LPTIM_CR,
> +			     STM32_LPTIM_SNGSTRT | STM32_LPTIM_ENABLE);

The regmap config in stm32-lptimer is not defined with the fast_io flag
(on purpose or not?) that means we can potentially deadlock here as the
lock is a mutex.

Isn't it detected with the lock validation scheme?

> +	return 0;
> +}
> +static int stm32_clkevent_lp_remove(struct platform_device *pdev)
> +{
> +	return -EBUSY; /* cannot unregister clockevent */
> +}

Won't be the mfd into an inconsistent state here? The other subsystems
will be removed but this one will prevent to unload the module leading
to a situation where the mfd is partially removed but still there
without a possible recovery, no?

> +static const struct of_device_id stm32_clkevent_lp_of_match[] = {
> +	{ .compatible = "st,stm32-lptimer-timer", },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, stm32_clkevent_lp_of_match);
> +
> +static struct platform_driver stm32_clkevent_lp_driver = {
> +	.probe	= stm32_clkevent_lp_probe,
> +	.remove = stm32_clkevent_lp_remove,
> +	.driver	= {
> +		.name = "stm32-lptimer-timer",
> +		.of_match_table = of_match_ptr(stm32_clkevent_lp_of_match),
> +	},
> +};


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