Re: [PATCH v3 2/2] clocksource: Add Low Power STM32 timers driver

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

Hi Benjamin,

On Tue, Jan 28, 2020 at 01:07:02PM +0100, Benjamin Gaignard wrote:
> From: Benjamin Gaignard <benjamin.gaignard@linaro.org>
> 
> Implement clock event driver using low power STM32 timers.
> Low power timers counter s running even in when CPU is in stop mode.

Can you fix the sentence above?

> 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.

Please give a description of the timer (eg. e37e45934afed).
 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
> Signed-off-by: Pascal Paillet <p.paillet@st.com>
> ---
> version 3:
> - fix timer set sequence
> - don't forget to free irq on remove function
> - use devm_kzalloc to simplify errors handling in probe function
> 
>  drivers/clocksource/Kconfig          |   4 +
>  drivers/clocksource/Makefile         |   1 +
>  drivers/clocksource/timer-stm32-lp.c | 248 +++++++++++++++++++++++++++++++++++
>  3 files changed, 253 insertions(+)
>  create mode 100644 drivers/clocksource/timer-stm32-lp.c
> 
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index 5fdd76cb1768..d9d06c14777d 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -292,6 +292,10 @@ config CLKSRC_STM32
>  	select CLKSRC_MMIO
>  	select TIMER_OF
>  
> +config CLKSRC_STM32_LP
> +	bool "Low power clocksource for STM32 SoCs"

(silent option)

> +	depends on OF && ARM && (MACH_STM32MP157 || COMPILE_TEST)

Do you really want to make this option? This timer belongs to a mfd, so if the
mfd is enabled it should enable the timer also, no ?

> +
>  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 4dfe4225ece7..c6eef37be9cc 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..b6de1ca9e115
> --- /dev/null
> +++ b/drivers/clocksource/timer-stm32-lp.c
> @@ -0,0 +1,248 @@
> +// 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/clocksource.h>
> +#include <linux/clockchips.h>
> +#include <linux/delay.h>
> +#include <linux/irq.h>
> +#include <linux/interrupt.h>
> +#include <linux/iopoll.h>
> +#include <linux/kernel.h>
> +#include <linux/mfd/stm32-lptimer.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_address.h>
> +#include <linux/of_irq.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>

Please check the headers above, all are not needed IMO.

> +#define LPTIM_ICR		0x04
> +#define ICR_ARRMCF		BIT(1)
> +
> +#define LPTIM_IER		0x08
> +#define IER_ARRMIE		BIT(1)
> +
> +#define LPTIM_CFGR		0x0C
> +#define CFGR_PSC_OFFSET		9
> +
> +#define LPTIM_CR		0x10
> +#define CR_ENABLE		BIT(0)
> +#define CR_SNGSTRT		BIT(1)
> +#define CR_CNTSTRT		BIT(2)
> +
> +#define LPTIM_CMP		0x14
> +#define LPTIM_ARR		0x18
> +
> +#define STM32_LP_BITS		16
> +#define STM32_LP_RATING		400
> +#define STM32_CLKRATE		(32000 * HZ)
> +#define TIMER_MAX_VAL		(BIT(STM32_LP_BITS) - 1)

STM32 prefix missing

> +#define STM32_LP_MAX_PSC	7
> +
> +struct stm32_lp_private {
> +	struct regmap *reg;
> +	struct clk *clk;
> +	struct clock_event_device clkevt;
> +	unsigned long rate;

This field can be saved if the parameter is passed to the set_prescalar
function.

> +	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, LPTIM_CR, 0);
> +	regmap_write(priv->reg, LPTIM_IER, 0);
> +	/* clear pending flags */
> +	regmap_write(priv->reg, LPTIM_ICR, ICR_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 TIMER */
> +	regmap_write(priv->reg, LPTIM_CR, 0);
> +	/* enable ARR interrupt */
> +	regmap_write(priv->reg, LPTIM_IER, IER_ARRMIE);
> +	/* enable LPTIMER*/
> +	regmap_write(priv->reg, LPTIM_CR, CR_ENABLE);
> +	/* set nex event counter */
> +	regmap_write(priv->reg, LPTIM_ARR, evt);
> +	/* reset counter */
> +	regmap_write(priv->reg, LPTIM_CMP, 0);
> +
> +	/* start counter */
> +	if (is_periodic)
> +		regmap_write(priv->reg, LPTIM_CR, CR_CNTSTRT | CR_ENABLE);
> +	else
> +		regmap_write(priv->reg, LPTIM_CR, CR_SNGSTRT | CR_ENABLE);

Please merge all these calls to regmap_write into a single one to reduce
contention.

> +	return 0;
> +}
> +
> +static int stm32_clkevent_lp_set_next_event(unsigned long evt,
> +					    struct clock_event_device *clkevt)
> +{
> +	return stm32_clkevent_lp_set_timer(evt, clkevt,
> +					   clockevent_state_periodic(clkevt));
> +}
> +
> +static int stm32_clkevent_lp_set_periodic(struct clock_event_device *clkevt)
> +{
> +	struct stm32_lp_private *priv = to_priv(clkevt);
> +
> +	return stm32_clkevent_lp_set_timer(priv->period, clkevt, true);
> +}
> +
> +static int stm32_clkevent_lp_set_oneshot(struct clock_event_device *clkevt)
> +{
> +	struct stm32_lp_private *priv = to_priv(clkevt);
> +
> +	return stm32_clkevent_lp_set_timer(priv->period, clkevt, false);
> +}
> +
> +static irqreturn_t stm32_clkevent_lp_irq_handler(int irq, void *dev_id)
> +{
> +	struct clock_event_device *clkevt = (struct clock_event_device *)dev_id;
> +	struct stm32_lp_private *priv = to_priv(clkevt);
> +
> +	regmap_write(priv->reg, LPTIM_ICR, ICR_ARRMCF);
> +
> +	clkevt->event_handler(clkevt);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +/**

This is a kerneldoc format

> + * stm32_clkevent_lp_set_prescaler - Compute and set the prescaler register
> + * @priv: a pointer to a timer-of structure
> + *
> + * Compute the prescaler to always target a 32Khz timer rate
> + */

Given these are static callbacks, you can drop the function description by
moving it to a comment in the function. 

> +static void stm32_clkevent_lp_set_prescaler(struct stm32_lp_private *priv)
> +{
> +	int i;
> +
> +	for (i = 0; i <= STM32_LP_MAX_PSC; i++) {
> +		if (DIV_ROUND_CLOSEST(priv->rate, 1 << i) < STM32_CLKRATE)
> +			break;
> +	}
> +
> +	regmap_write(priv->reg, LPTIM_CFGR, i << CFGR_PSC_OFFSET);
> +
> +	/* Adjust rate and period given the prescaler value */
> +	priv->rate = DIV_ROUND_CLOSEST(priv->rate, (1 << i));
> +	priv->period = DIV_ROUND_UP(priv->rate, HZ);
> +}
> +
> +static int stm32_clkevent_lp_init(struct stm32_lp_private *priv,
> +				  struct device_node *np)
> +{
> +	int ret;
> +
> +	priv->clkevt.name = np->full_name;
> +	priv->clkevt.cpumask = cpu_possible_mask;
> +	priv->clkevt.features = CLOCK_EVT_FEAT_PERIODIC |
> +				CLOCK_EVT_FEAT_ONESHOT;
> +	priv->clkevt.set_state_shutdown = stm32_clkevent_lp_shutdown;
> +	priv->clkevt.set_state_periodic = stm32_clkevent_lp_set_periodic;
> +	priv->clkevt.set_state_oneshot = stm32_clkevent_lp_set_oneshot;
> +	priv->clkevt.set_next_event = stm32_clkevent_lp_set_next_event;
> +	priv->clkevt.rating = STM32_LP_RATING;
> +
> +	priv->clkevt.irq = irq_of_parse_and_map(np, 0);
> +	if (!priv->clkevt.irq)
> +		return -EINVAL;
> +
> +	ret = request_irq(priv->clkevt.irq, stm32_clkevent_lp_irq_handler,
> +			  IRQF_TIMER, np->full_name, &priv->clkevt);
> +	if (ret)
> +		return ret;

May be move the node parsing to the 'probe' function and use demv_request_irq
(or use timer-of)?

Pass the timer name as parameter to this function?

> +
> +	clockevents_config_and_register(&priv->clkevt, priv->rate, 0x1,
> +					TIMER_MAX_VAL);
> +
> +	return 0;
> +}
> +
> +static int stm32_clkevent_lp_probe(struct platform_device *pdev)
> +{
> +	struct stm32_lptimer *ddata = dev_get_drvdata(pdev->dev.parent);
> +	struct stm32_lp_private *priv;
> +	int ret;
> +
> +	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	priv->reg = ddata->regmap;
> +	priv->clk = ddata->clk;
> +	ret = clk_prepare_enable(priv->clk);
> +	if (ret)
> +		return -EINVAL;
> +
> +	priv->rate = clk_get_rate(priv->clk);
> +	if (!priv->rate)
> +		goto out_clk_disable;
> +
> +	stm32_clkevent_lp_set_prescaler(priv);
> +
> +	ret = stm32_clkevent_lp_init(priv, pdev->dev.parent->of_node);
> +	if (ret)
> +		goto out_clk_disable;
> +
> +	platform_set_drvdata(pdev, priv);

See if this is needed given the comment below about the removal.

> +	return 0;
> +
> +out_clk_disable:
> +	clk_disable_unprepare(priv->clk);
> +
> +	return -EINVAL;
> +}
> +
> +static int stm32_clkevent_lp_remove(struct platform_device *pdev)
> +{
> +	struct stm32_lp_private *priv = platform_get_drvdata(pdev);
> +
> +	clk_disable_unprepare(priv->clk);
> +	free_irq(priv->clkevt.irq, &priv->clkevt);
> +
> +	return 0;
> +}

This is broken IMO, the time framework will continue considering the previously
registered clockevent as available. You should consider converting the mfd to a
bool instead of a tristate (and remove the dead code).

> +static const struct of_device_id stm32_clkevent_lp_of_match[] = {
> +	{ .compatible = "st,stm32-clkevent-lp", },
> +	{},
> +};
> +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-clkevent-lp",
> +		.of_match_table = of_match_ptr(stm32_clkevent_lp_of_match),
> +	},
> +};
> +module_platform_driver(stm32_clkevent_lp_driver);
> +
> +MODULE_ALIAS("platform:stm32-clkevent-lp");
> +MODULE_DESCRIPTION("STMicroelectronics STM32 clockevent LP driver");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.15.0
> 

-- 

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