Subject: Re: [PATCH 2/5] clocksource/drivers/timer-microchip-pit64b: add Microchip PIT64B support

From: Alexandre Belloni <[email-masked]>
Date: Mon, 8 Apr 2019 14:11:41 +0200

Hi Daniel,

On 08/04/2019 10:43:26+0200, Daniel Lezcano wrote:
> Hi Claudiu,
> 
> On 14/03/2019 17:26, [email-masked] wrote:
> > From: Claudiu Beznea <[email-masked]>
> > 
> > Add driver for Microchip PIT64B timer. Timer could be used in continuous
> > mode or oneshot mode. The hardware has 2x32 bit registers for period
> > emulating a 64 bit timer. The LSB_PR and MSB_PR registers are used to set
> > the period value (compare value). TLSB and TMSB keeps the current value
> > of the counter. After a compare the TLSB and TMSB register resets. Apart
> > from this the hardware has SMOD bit in mode register that allow to
> > reconfigure the timer without reset and start commands (start command
> > while timer is active is ignored).
> > The driver uses PIT64B timer as clocksource or clockevent. First requested
> > timer would be registered as clockevent, second one would be registered as
> > clocksource.
> 
> Even if that was done this way before, assuming the DT describes the
> clockevent at the first place and then the clocksource, it is a fragile
> approach.
> 
> What about using one of these approach?
> 
> eg.
> 
> arch/arm/boot/dts/at91sam9261ek.dts
> 
> chosen {
> 	bootargs = "rootfstype=ubifs ubi.mtd=5 root=ubi0:rootfs rw";
>                 stdout-path = "serial0:115200n8";
> 
> 	clocksource {
> 		timer = <&timer0>;
> 	};
> 
>         clockevent {
> 		timer = <&timer1>;
>         };
> };
> 

I suggested and implemented exactly that back in 2017 and it was shot
down by both Rob and Mark:

https://lore.kernel.org/lkml/[email-masked]/

At the time, you didn't do *anything* to get it accepted, you stayed
silent. I can respin the series but then I see two options:
 - either you back up the series and really push for it
 - or you simply take this driver as it is. There is nothing in it that
   couldn't be reworked later once you reached a conclusion with the DT
maintainers.

> or
> 
> arch/arm/boot/dts/integratorap.dts
> 
> aliases {
> 	arm,timer-primary = &timer2;
> 	arm,timer-secondary = &timer1;
> };
> 
> So we can have control of what is the clocksource or the clockevent.
> That is particulary handy in case of multiple channels.
> 
> Not sure if we can replace the 'arm,timer_primary' to 'clocksource'.
> 
> Rob? What is your opinion?
> 
> > Individual PIT64B hardware resources were used for clocksource
> > and clockevent to be able to support high resolution timers with this
> > hardware implementation.
> > 
> > Signed-off-by: Claudiu Beznea <[email-masked]>
> > ---
> >  drivers/clocksource/Kconfig                  |   6 +
> >  drivers/clocksource/Makefile                 |   1 +
> >  drivers/clocksource/timer-microchip-pit64b.c | 464 +++++++++++++++++++++++++++
> >  3 files changed, 471 insertions(+)
> >  create mode 100644 drivers/clocksource/timer-microchip-pit64b.c
> > 
> > diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> > index 5d93e580e5dc..2ad6f881a0bb 100644
> > --- a/drivers/clocksource/Kconfig
> > +++ b/drivers/clocksource/Kconfig
> > @@ -448,6 +448,12 @@ config OXNAS_RPS_TIMER
> >  config SYS_SUPPORTS_SH_CMT
> >          bool
> >  
> > +config MICROCHIP_PIT64B
> > +	bool "Microchip PIT64B support"
> > +	depends on OF || COMPILE_TEST
> > +	help
> > +	  This option enables Microchip PIT64B timer.
> > +
> >  config MTK_TIMER
> >  	bool "Mediatek timer driver" if COMPILE_TEST
> >  	depends on HAS_IOMEM
> > diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> > index c4a8e9ef932a..c53fa12b9b94 100644
> > --- a/drivers/clocksource/Makefile
> > +++ b/drivers/clocksource/Makefile
> > @@ -35,6 +35,7 @@ obj-$(CONFIG_U300_TIMER)	+= timer-u300.o
> >  obj-$(CONFIG_SUN4I_TIMER)	+= timer-sun4i.o
> >  obj-$(CONFIG_SUN5I_HSTIMER)	+= timer-sun5i.o
> >  obj-$(CONFIG_MESON6_TIMER)	+= timer-meson6.o
> > +obj-$(CONFIG_MICROCHIP_PIT64B)	+= timer-microchip-pit64b.o
> >  obj-$(CONFIG_TEGRA_TIMER)	+= timer-tegra20.o
> >  obj-$(CONFIG_VT8500_TIMER)	+= timer-vt8500.o
> >  obj-$(CONFIG_NSPIRE_TIMER)	+= timer-zevio.o
> > diff --git a/drivers/clocksource/timer-microchip-pit64b.c b/drivers/clocksource/timer-microchip-pit64b.c
> > new file mode 100644
> > index 000000000000..6787aa98ef01
> > --- /dev/null
> > +++ b/drivers/clocksource/timer-microchip-pit64b.c
> > @@ -0,0 +1,464 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +//
> > +// Copyright (C) 2019 Microchip Technology Inc.
> > +// Copyright (C) 2019 Claudiu Beznea ([email-masked])
> > +
> > +#include <linux/clk.h>
> > +#include <linux/clockchips.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/of_address.h>
> > +#include <linux/of_irq.h>
> > +#include <linux/sched_clock.h>
> > +#include <linux/slab.h>
> > +
> > +#define MCHP_PIT64B_CR		0x00	/* Control Register */
> > +#define MCHP_PIT64B_CR_START	BIT(0)
> > +#define MCHP_PIT64B_CR_SWRST	BIT(8)
> > +
> > +#define MCHP_PIT64B_MR		0x04	/* Mode Register */
> > +#define MCHP_PIT64B_MR_CONT	BIT(0)
> > +#define MCHP_PIT64B_MR_SGCLK	BIT(3)
> > +#define MCHP_PIT64B_MR_SMOD	BIT(4)
> > +#define MCHP_PIT64B_MR_PRES	GENMASK(11, 8)
> > +
> > +#define MCHP_PIT64B_LSB_PR	0x08	/* LSB Period Register */
> > +
> > +#define MCHP_PIT64B_MSB_PR	0x0C	/* MSB Period Register */
> > +
> > +#define MCHP_PIT64B_IER		0x10	/* Interrupt Enable Register */
> > +#define MCHP_PIT64B_IER_PERIOD	BIT(0)
> > +
> > +#define MCHP_PIT64B_ISR		0x1C	/* Interrupt Status Register */
> > +#define MCHP_PIT64B_ISR_PERIOD	BIT(0)
> > +
> > +#define MCHP_PIT64B_TLSBR	0x20	/* Timer LSB Register */
> > +
> > +#define MCHP_PIT64B_TMSBR	0x24	/* Timer MSB Register */
> > +
> > +#define MCHP_PIT64B_PRES_MAX	0x10
> > +#define MCHP_PIT64B_DEF_FREQ	2500000UL	/* 2.5 MHz */
> > +#define MCHP_PIT64B_LSBMASK	GENMASK_ULL(31, 0)
> > +#define MCHP_PIT64B_PRESCALER(p)	(MCHP_PIT64B_MR_PRES & ((p) << 8))
> > +
> > +#define MCHP_PIT64B_NAME	"pit64b"
> > +
> > +struct mchp_pit64b_common_data {
> > +	void __iomem *base;
> > +	struct clk *pclk;
> > +	struct clk *gclk;
> > +	u64 cycles;
> > +	u8 pres;
> > +};
> > +
> > +struct mchp_pit64b_clksrc_data {
> > +	struct clocksource *clksrc;
> > +	struct mchp_pit64b_common_data *cd;
> > +};
> > +
> > +struct mchp_pit64b_clkevt_data {
> > +	struct clock_event_device *clkevt;
> > +	struct mchp_pit64b_common_data *cd;
> > +};
> > +
> > +static struct mchp_pit64b_data {
> > +	struct mchp_pit64b_clksrc_data *csd;
> > +	struct mchp_pit64b_clkevt_data *ced;
> > +} data;
> > +
> > +static inline u32 mchp_pit64b_read(void __iomem *base, u32 offset)
> > +{
> > +	return readl_relaxed(base + offset);
> > +}
> > +
> > +static inline void mchp_pit64b_write(void __iomem *base, u32 offset, u32 val)
> > +{
> > +	writel_relaxed(val, base + offset);
> > +}
> > +
> > +static inline u64 mchp_pit64b_get_period(void __iomem *base)
> > +{
> > +	u32 lsb, msb;
> > +
> > +	/* LSB must be read first to guarantee an atomic read of the 64 bit
> > +	 * timer.
> > +	 */
> > +	lsb = mchp_pit64b_read(base, MCHP_PIT64B_TLSBR);
> > +	msb = mchp_pit64b_read(base, MCHP_PIT64B_TMSBR);
> > +
> > +	return (((u64)msb << 32) | lsb);
> > +}
> > +
> > +static inline void mchp_pit64b_set_period(void __iomem *base, u64 cycles)
> > +{
> > +	u32 lsb, msb;
> > +
> > +	lsb = cycles & MCHP_PIT64B_LSBMASK;
> > +	msb = cycles >> 32;
> > +
> > +	/* LSB must be write last to guarantee an atomic update of the timer
> > +	 * even when SMOD=1.
> > +	 */
> > +	mchp_pit64b_write(base, MCHP_PIT64B_MSB_PR, msb);
> > +	mchp_pit64b_write(base, MCHP_PIT64B_LSB_PR, lsb);
> > +}
> > +
> > +static inline void mchp_pit64b_reset(struct mchp_pit64b_common_data *data,
> > +				     u32 mode, bool irq_ena)
> > +{
> > +	mode |= MCHP_PIT64B_PRESCALER(data->pres);
> > +	if (data->gclk)
> > +		mode |= MCHP_PIT64B_MR_SGCLK;
> > +
> > +	mchp_pit64b_write(data->base, MCHP_PIT64B_CR, MCHP_PIT64B_CR_SWRST);
> > +	mchp_pit64b_write(data->base, MCHP_PIT64B_MR, mode);
> > +	mchp_pit64b_set_period(data->base, data->cycles);
> > +	if (irq_ena)
> > +		mchp_pit64b_write(data->base, MCHP_PIT64B_IER,
> > +				  MCHP_PIT64B_IER_PERIOD);
> > +	mchp_pit64b_write(data->base, MCHP_PIT64B_CR, MCHP_PIT64B_CR_START);
> > +}
> > +
> > +static u64 mchp_pit64b_read_clk(struct clocksource *cs)
> > +{
> > +	return mchp_pit64b_get_period(data.csd->cd->base);
> > +}
> > +
> > +static u64 mchp_sched_read_clk(void)
> > +{
> > +	return mchp_pit64b_get_period(data.csd->cd->base);
> > +}
> > +
> > +static struct clocksource mchp_pit64b_clksrc = {
> > +	.name = MCHP_PIT64B_NAME,
> > +	.mask = CLOCKSOURCE_MASK(64),
> > +	.flags = CLOCK_SOURCE_IS_CONTINUOUS,
> > +	.rating = 210,
> > +	.read = mchp_pit64b_read_clk,
> > +};
> > +
> > +static int mchp_pit64b_clkevt_shutdown(struct clock_event_device *cedev)
> > +{
> > +	mchp_pit64b_write(data.ced->cd->base, MCHP_PIT64B_CR,
> > +			  MCHP_PIT64B_CR_SWRST);
> > +
> > +	return 0;
> > +}
> > +
> > +static int mchp_pit64b_clkevt_set_periodic(struct clock_event_device *cedev)
> > +{
> > +	mchp_pit64b_reset(data.ced->cd, MCHP_PIT64B_MR_CONT, true);
> > +
> > +	return 0;
> > +}
> > +
> > +static int mchp_pit64b_clkevt_set_oneshot(struct clock_event_device *cedev)
> > +{
> > +	mchp_pit64b_reset(data.ced->cd, MCHP_PIT64B_MR_SMOD, true);
> > +
> > +	return 0;
> > +}
> > +
> > +static int mchp_pit64b_clkevt_set_next_event(unsigned long evt,
> > +					     struct clock_event_device *cedev)
> > +{
> > +	mchp_pit64b_set_period(data.ced->cd->base, evt);
> > +	mchp_pit64b_write(data.ced->cd->base, MCHP_PIT64B_CR,
> > +			  MCHP_PIT64B_CR_START);
> > +
> > +	return 0;
> > +}
> > +
> > +static void mchp_pit64b_clkevt_suspend(struct clock_event_device *cedev)
> > +{
> > +	mchp_pit64b_write(data.ced->cd->base, MCHP_PIT64B_CR,
> > +			  MCHP_PIT64B_CR_SWRST);
> > +	if (data.ced->cd->gclk)
> > +		clk_disable_unprepare(data.ced->cd->gclk);
> > +	clk_disable_unprepare(data.ced->cd->pclk);
> > +}
> > +
> > +static void mchp_pit64b_clkevt_resume(struct clock_event_device *cedev)
> > +{
> > +	u32 mode = MCHP_PIT64B_MR_SMOD;
> > +
> > +	clk_prepare_enable(data.ced->cd->pclk);
> > +	if (data.ced->cd->gclk)
> > +		clk_prepare_enable(data.ced->cd->gclk);
> > +
> > +	if (clockevent_state_periodic(data.ced->clkevt))
> > +		mode = MCHP_PIT64B_MR_CONT;
> > +
> > +	mchp_pit64b_reset(data.ced->cd, mode, true);
> > +}
> > +
> > +static struct clock_event_device mchp_pit64b_clkevt = {
> > +	.name = MCHP_PIT64B_NAME,
> > +	.features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_PERIODIC,
> > +	.rating = 150,
> > +	.set_state_shutdown = mchp_pit64b_clkevt_shutdown,
> > +	.set_state_periodic = mchp_pit64b_clkevt_set_periodic,
> > +	.set_state_oneshot = mchp_pit64b_clkevt_set_oneshot,
> > +	.set_next_event = mchp_pit64b_clkevt_set_next_event,
> > +	.suspend = mchp_pit64b_clkevt_suspend,
> > +	.resume = mchp_pit64b_clkevt_resume,
> > +};
> > +
> > +static irqreturn_t mchp_pit64b_interrupt(int irq, void *dev_id)
> > +{
> > +	struct mchp_pit64b_clkevt_data *irq_data = dev_id;
> > +
> > +	if (data.ced != irq_data)
> > +		return IRQ_NONE;
> > +
> > +	if (mchp_pit64b_read(irq_data->cd->base, MCHP_PIT64B_ISR) &
> > +	    MCHP_PIT64B_ISR_PERIOD) {
> > +		irq_data->clkevt->event_handler(irq_data->clkevt);
> > +		return IRQ_HANDLED;
> > +	}
> > +
> > +	return IRQ_NONE;
> > +}
> > +
> > +static int __init mchp_pit64b_pres_compute(u32 *pres, u32 clk_rate,
> > +					   u32 max_rate)
> > +{
> > +	u32 tmp;
> > +
> > +	for (*pres = 0; *pres < MCHP_PIT64B_PRES_MAX; (*pres)++) {
> > +		tmp = clk_rate / (*pres + 1);
> > +		if (tmp <= max_rate)
> > +			break;
> > +	}
> > +
> > +	if (*pres == MCHP_PIT64B_PRES_MAX)
> > +		return -EINVAL;
> > +
> > +	return 0;
> > +}
> > +
> > +static int __init mchp_pit64b_pres_prepare(struct mchp_pit64b_common_data *cd,
> > +					   unsigned long max_rate)
> > +{
> > +	unsigned long pclk_rate, diff = 0, best_diff = ULONG_MAX;
> > +	long gclk_round = 0;
> > +	u32 pres, best_pres;
> > +	int ret = 0;
> > +
> > +	pclk_rate = clk_get_rate(cd->pclk);
> > +	if (!pclk_rate)
> > +		return -EINVAL;
> > +
> > +	if (cd->gclk) {
> > +		gclk_round = clk_round_rate(cd->gclk, max_rate);
> > +		if (gclk_round < 0)
> > +			goto pclk;
> > +
> > +		if (pclk_rate / gclk_round < 3)
> > +			goto pclk;
> > +
> > +		ret = mchp_pit64b_pres_compute(&pres, gclk_round, max_rate);
> > +		if (ret)
> > +			best_diff = abs(gclk_round - max_rate);
> > +		else
> > +			best_diff = abs(gclk_round / (pres + 1) - max_rate);
> > +		best_pres = pres;
> > +	}
> > +
> > +pclk:
> > +	/* Check if requested rate could be obtained using PCLK. */
> > +	ret = mchp_pit64b_pres_compute(&pres, pclk_rate, max_rate);
> > +	if (ret)
> > +		diff = abs(pclk_rate - max_rate);
> > +	else
> > +		diff = abs(pclk_rate / (pres + 1) - max_rate);
> > +
> > +	if (best_diff > diff) {
> > +		/* Use PCLK. */
> > +		cd->gclk = NULL;
> > +		best_pres = pres;
> > +	} else {
> > +		clk_set_rate(cd->gclk, gclk_round);
> > +	}
> > +
> > +	cd->pres = best_pres;
> > +
> > +	pr_info("PIT64B: using clk=%s with prescaler %u, freq=%lu [Hz]\n",
> > +		cd->gclk ? "gclk" : "pclk", cd->pres,
> > +		cd->gclk ? gclk_round / (cd->pres + 1)
> > +			 : pclk_rate / (cd->pres + 1));
> > +
> > +	return 0;
> > +}
> > +
> > +static int __init mchp_pit64b_dt_init_clksrc(struct mchp_pit64b_common_data *cd)
> > +{
> > +	struct mchp_pit64b_clksrc_data *csd;
> > +	unsigned long clk_rate;
> > +	int ret;
> > +
> > +	csd = kzalloc(sizeof(*csd), GFP_KERNEL);
> > +	if (!csd)
> > +		return -ENOMEM;
> > +
> > +	csd->cd = cd;
> > +
> > +	if (csd->cd->gclk)
> > +		clk_rate = clk_get_rate(csd->cd->gclk);
> > +	else
> > +		clk_rate = clk_get_rate(csd->cd->pclk);
> > +
> > +	clk_rate = clk_rate / (cd->pres + 1);
> > +	csd->cd->cycles = ULLONG_MAX;
> > +	mchp_pit64b_reset(csd->cd, MCHP_PIT64B_MR_CONT, false);
> > +
> > +	data.csd = csd;
> > +
> > +	csd->clksrc = &mchp_pit64b_clksrc;
> > +
> > +	ret = clocksource_register_hz(csd->clksrc, clk_rate);
> > +	if (ret) {
> > +		pr_debug("clksrc: Failed to register PIT64B clocksource!\n");
> > +		goto free;
> > +	}
> > +
> > +	sched_clock_register(mchp_sched_read_clk, 64, clk_rate);
> > +
> > +	return 0;
> > +
> > +free:
> > +	kfree(csd);
> > +	data.csd = NULL;
> > +
> > +	return ret;
> > +}
> > +
> > +static int __init mchp_pit64b_dt_init_clkevt(struct mchp_pit64b_common_data *cd,
> > +					     u32 irq)
> > +{
> > +	struct mchp_pit64b_clkevt_data *ced;
> > +	unsigned long clk_rate;
> > +	int ret;
> > +
> > +	ced = kzalloc(sizeof(*ced), GFP_KERNEL);
> > +	if (!ced)
> > +		return -ENOMEM;
> > +
> > +	ced->cd = cd;
> > +
> > +	if (ced->cd->gclk)
> > +		clk_rate = clk_get_rate(ced->cd->gclk);
> > +	else
> > +		clk_rate = clk_get_rate(ced->cd->pclk);
> > +
> > +	clk_rate = clk_rate / (ced->cd->pres + 1);
> > +	ced->cd->cycles = DIV_ROUND_CLOSEST(clk_rate, HZ);
> > +
> > +	ret = request_irq(irq, mchp_pit64b_interrupt, IRQF_TIMER, "pit64b_tick",
> > +			  ced);
> > +	if (ret) {
> > +		pr_debug("clkevt: Failed to setup PIT64B IRQ\n");
> > +		goto free;
> > +	}
> > +
> > +	data.ced = ced;
> > +
> > +	/* Set up and register clockevents. */
> > +	ced->clkevt = &mchp_pit64b_clkevt;
> > +	ced->clkevt->cpumask = cpumask_of(0);
> > +	ced->clkevt->irq = irq;
> > +	clockevents_config_and_register(ced->clkevt, clk_rate, 1, ULONG_MAX);
> > +
> > +	return 0;
> > +
> > +free:
> > +	kfree(ced);
> > +	data.ced = NULL;
> > +
> > +	return ret;
> > +}
> > +
> > +static int __init mchp_pit64b_dt_init(struct device_node *node)
> > +{
> > +	struct mchp_pit64b_common_data *cd;
> > +	u32 irq, freq = MCHP_PIT64B_DEF_FREQ;
> > +	int ret;
> > +
> > +	if (data.csd && data.ced)
> > +		return -EBUSY;
> > +
> > +	cd = kzalloc(sizeof(*cd), GFP_KERNEL);
> > +	if (!cd)
> > +		return -ENOMEM;
> > +
> > +	cd->pclk = of_clk_get_by_name(node, "pclk");
> > +	if (IS_ERR(cd->pclk)) {
> > +		ret = PTR_ERR(cd->pclk);
> > +		goto free;
> > +	}
> > +
> > +	cd->gclk = of_clk_get_by_name(node, "gclk");
> > +	if (IS_ERR(cd->gclk))
> > +		cd->gclk = NULL;
> > +
> > +	ret = of_property_read_u32(node, "clock-frequency", &freq);
> > +	if (ret)
> > +		pr_debug("PIT64B: failed to read clock frequency. Using default!\n");
> > +
> > +	ret = mchp_pit64b_pres_prepare(cd, freq);
> > +	if (ret)
> > +		goto free;
> > +
> > +	cd->base = of_iomap(node, 0);
> > +	if (!cd->base) {
> > +		pr_debug("%s: Could not map PIT64B address!\n",
> > +			 MCHP_PIT64B_NAME);
> > +		ret = -ENXIO;
> > +		goto free;
> > +	}
> > +
> > +	ret = clk_prepare_enable(cd->pclk);
> > +	if (ret)
> > +		goto unmap;
> > +
> > +	if (cd->gclk) {
> > +		ret = clk_prepare_enable(cd->gclk);
> > +		if (ret)
> > +			goto pclk_unprepare;
> > +	}
> > +
> > +	if (!data.ced) {
> > +		irq = irq_of_parse_and_map(node, 0);
> > +		if (!irq) {
> > +			pr_debug("%s: Failed to get PIT64B clockevent IRQ!\n",
> > +				 MCHP_PIT64B_NAME);
> > +			ret = -ENODEV;
> > +			goto gclk_unprepare;
> > +		}
> > +		ret = mchp_pit64b_dt_init_clkevt(cd, irq);
> > +		if (ret)
> > +			goto irq_unmap;
> > +	} else {
> > +		ret = mchp_pit64b_dt_init_clksrc(cd);
> > +		if (ret)
> > +			goto gclk_unprepare;
> > +	}
> > +
> > +	return 0;
> > +
> > +irq_unmap:
> > +	irq_dispose_mapping(irq);
> > +gclk_unprepare:
> > +	if (cd->gclk)
> > +		clk_disable_unprepare(cd->gclk);
> > +pclk_unprepare:
> > +	clk_disable_unprepare(cd->pclk);
> > +unmap:
> > +	iounmap(cd->base);
> > +free:
> > +	kfree(cd);
> > +
> > +	return ret;
> > +}
> > +
> > +TIMER_OF_DECLARE(mchp_pit64b_clksrc, "microchip,sam9x60-pit64b",
> > +		 mchp_pit64b_dt_init);
> > 
> 
> 
> -- 
>  <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
> 
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> <http://www.linaro.org/linaro-blog/> Blog
> 

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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