[PATCH v3 0/2] add Microchip PIT64B timer

[PATCH v3 0/2] add Microchip PIT64B timer

[Claudiu Beznea]

Hi,

This series adds driver for Microchip PIT64B timer.
Timer could be used in continuous or oneshot mode. It has 2x32 bit registers
to emulate a 64 bit timer. The timer's period could be configured via LSB_PR
and MSB_PR registers. The current timer's value could be checked via TLSB and
TMSB registers. When (TMSB << 32) | TLSB value reach the (MSB_PR << 32) | LSB_PR
interrupt is raised. If in contiuous mode the TLSB and TMSB resets and restart
counting.

This drivers uses PIT64B capabilities for clocksource and clockevent.
The first requested PIT64B timer is used for clockevent. The second one is used
for clocksource. Individual PIT64B hardware resources were used for clocksource
and clockevent to be able to support high resolution timers with this PIT64B
implementation.

Thank you,
Claudiu Beznea

Changes in v3:
- rework data structures:
	- timer related data structure is called now mchp_pit64b_timer embedding
	  base iomem, clocks, interrupt, prescaler value
	- introduced struct mchp_pit64b_clksrc and struct mchp_pit64b_clkevt
	  instead of mchp_pit64b_clksrc_data and mchp_pit64b_clkevt_data
	- use container_of() to retrieve mchp_pit64b_timer objects on
	  clocksource/clockevent specific APIs
	- document data structures
- use raw_local_irq_save()/raw_local_irq_restore() when reading
  MCHP_PIT64B_TLSBR and MCHP_PIT64B_TMSBR in mchp_pit64b_get_period()
- get rid of mchp_pit64b_read(), mchp_pit64b_write() and use instead
  readl_relaxed(), writel_relaxed()
- get rid of mchp_pit64b_set_period() and inlined its instructions in
  mchp_pit64b_reset()
- mchp_pit64b_reset() gets now as arguments an object of type
  struct mchp_pit64b_timer, cycles to program and mode
- remove static struct clocksource mchp_pit64b_clksrc and
  static struct clock_event_device mchp_pit64b_clkevt and instead allocate
  and fill them in mchp_pit64b_dt_init_clksrc() and
  mchp_pit64b_dt_init_clkevt()
- call mchp_pit64b_reset() in mchp_pit64b_clkevt_set_next_event() and
  program clockevent timer with SMOD=0; if SMOD=1 the timer's period could
  be reprogrammed also if writing TLSB, TMSB if it is running. In cases
  were its period expired START bit still has to be set in control register.
  In case the programming sequence is like in v2, with SMOD=1:
	- program MSB_PR
	- program LSB_PR
	- program START bit in control register
  for short programmed periods we may start the timer twice with this
  programming sequence, 1st time after LSB_PR is updated (and due to SMOD=1),
  2nd time after programming START bit in control register and in case
  programmed period already expire
- simplify mchp_pit64b_interrupt() by just reading ISR register, to clear the
  received interrupt, and just call irq_data->clkevt->event_handler(irq_data->clkevt);
- in mchp_pit64b_pres_compute() chose the bigest prescaler in case a good
  one not found
- document mchp_pit64b_pres_prepare() and simplified it a bit
- enforce gclk as mandatory
- introduce mchp_pit64b_timer_init() and mchp_pit64b_timer_cleanup()
- keep the clocksource timer base address in a mchp_pit64b_cs_base variable so
  that it could be used by mchp_pit64b_sched_read_clk()
- rework mchp_pit64b_dt_init() and return -EINVAL in case it was called
  more than two times: one for initialization of clockevent, one for
  initialization of clocksource
- introduce MCHP_PIT64B_MR_ONE_SHOT define
- move the new lines introduced in Makefile and Kconfig at the end of files
- collect Rob's Reviewed-by tag on patch 1/2
- review the commit message of patch 2/2

Changes in v2:
- remove clock-frequency DT binding and hardcoded it in the driver
- initialize best_pres variable in mchp_pit64b_pres_prepare()
- remove MCHP_PIT64B_DEF_FREQ 
- get rid of patches 3-5 from v1 [1] since there is no entry in MAINTAINERS file
  for this entry. It was removed in
  commit 44015a8181a5 ("MAINTAINERS: at91: remove the TC entry")

[1] https://lore.kernel.org/lkml/1552580772-8499-1-git-send-email-claudiu.beznea@microchip.com/

Claudiu Beznea (2):
  dt-bindings: arm: atmel: add bindings for PIT64B
  clocksource/drivers/timer-microchip-pit64b: add Microchip PIT64B
    support

 .../devicetree/bindings/arm/atmel-sysregs.txt      |   6 +
 drivers/clocksource/Kconfig                        |   6 +
 drivers/clocksource/Makefile                       |   1 +
 drivers/clocksource/timer-microchip-pit64b.c       | 501 +++++++++++++++++++++
 4 files changed, 514 insertions(+)
 create mode 100644 drivers/clocksource/timer-microchip-pit64b.c

-- 
2.7.4

[PATCH v3 1/2] dt-bindings: arm: atmel: add bindings for PIT64B

[Claudiu Beznea]

Add device tree bindings for PIT64B timer.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
---
 Documentation/devicetree/bindings/arm/atmel-sysregs.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/arm/atmel-sysregs.txt b/Documentation/devicetree/bindings/arm/atmel-sysregs.txt
index 9fbde401a090..e003a553b986 100644
--- a/Documentation/devicetree/bindings/arm/atmel-sysregs.txt
+++ b/Documentation/devicetree/bindings/arm/atmel-sysregs.txt
@@ -10,6 +10,12 @@ PIT Timer required properties:
 - interrupts: Should contain interrupt for the PIT which is the IRQ line
   shared across all System Controller members.
 
+PIT64B Timer required properties:
+- compatible: Should be "microchip,sam9x60-pit64b"
+- reg: Should contain registers location and length
+- interrupts: Should contain interrupt for PIT64B timer
+- clocks: Should contain the available clock sources for PIT64B timer.
+
 System Timer (ST) required properties:
 - compatible: Should be "atmel,at91rm9200-st", "syscon", "simple-mfd"
 - reg: Should contain registers location and length
-- 
2.7.4

[PATCH v3 2/2] clocksource/drivers/timer-microchip-pit64b: add Microchip PIT64B support

[Claudiu Beznea]

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.
The driver uses PIT64B timer for clocksource or clockevent. First
requested timer would be registered as clockevent, second one would be
registered as clocksource. 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 <claudiu.beznea@microchip.com>
---

Changes in v3:
- rework data structures:
	- timer related data structure is called now mchp_pit64b_timer embedding
	  base iomem, clocks, interrupt, prescaler value
	- introduced struct mchp_pit64b_clksrc and struct mchp_pit64b_clkevt
	  instead of mchp_pit64b_clksrc_data and mchp_pit64b_clkevt_data
	- use container_of() to retrieve mchp_pit64b_timer objects on
	  clocksource/clockevent specific APIs
	- document data structures
- use raw_local_irq_save()/raw_local_irq_restore() when reading
  MCHP_PIT64B_TLSBR and MCHP_PIT64B_TMSBR in mchp_pit64b_get_period()
- get rid of mchp_pit64b_read(), mchp_pit64b_write() and use instead
  readl_relaxed(), writel_relaxed()
- get rid of mchp_pit64b_set_period() and inlined its instructions in
  mchp_pit64b_reset()
- mchp_pit64b_reset() gets now as arguments an object of type
  struct mchp_pit64b_timer, cycles to program and mode
- remove static struct clocksource mchp_pit64b_clksrc and
  static struct clock_event_device mchp_pit64b_clkevt and instead allocate
  and fill them in mchp_pit64b_dt_init_clksrc() and
  mchp_pit64b_dt_init_clkevt()
- call mchp_pit64b_reset() in mchp_pit64b_clkevt_set_next_event() and
  program clockevent timer with SMOD=0; if SMOD=1 the timer's period could
  be reprogrammed also if writting TLSB, TMSB if it is running. In cases
  were its period expired START bit still has to be set in control register.
  In case the programming sequence is like in v2, with SMOD=1:
	- program MSB_PR
	- program LSB_PR
	- program START bit in control register
  for short programmed periods we may start the timer twice with this
  programming sequence, 1st time after LSB_PR is updated (and due to SMOD=1),
  2nd time after programming START bit in control register and in case
  programmed period already expire
- simplify mchp_pit64b_interrupt() by just reading ISR register, to clear the
  received interrupt, and just call irq_data->clkevt->event_handler(irq_data->clkevt);
- in mchp_pit64b_pres_compute() chose the bigest prescaler in case a good
  one not found
- document mchp_pit64b_pres_prepare() and simplified it a bit
- enforce gclk as mandatory
- introduce mchp_pit64b_timer_init() and mchp_pit64b_timer_cleanup()
- keep the clocksource timer base address in a mchp_pit64b_cs_base variable so
  that it could be used by mchp_pit64b_sched_read_clk()
- rework mchp_pit64b_dt_init() and return -EINVAL in case it was called
  more than two times: one for initialization of clockevent, one for
  initialization of clocksource
- introduce MCHP_PIT64B_MR_ONE_SHOT define
- move the new lines introduced in Makefile and Kconfig at the end of files
- collect Rob's Reviewed-by tag on patch 1/2
- review the commit message of patch 2/2

Changes in v2:
- remove clock-frequency DT binding and hardcoded it in the driver
- initialize best_pres variable in mchp_pit64b_pres_prepare()
- remove MCHP_PIT64B_DEF_FREQ 
- get rid of patches 3-5 from v1 [1] since there is no entry in MAINTAINERS file
  for this entry. It was removed in
  commit 44015a8181a5 ("MAINTAINERS: at91: remove the TC entry")

[1] https://lore.kernel.org/lkml/1552580772-8499-1-git-send-email-claudiu.beznea@microchip.com/

 drivers/clocksource/Kconfig                  |   6 +
 drivers/clocksource/Makefile                 |   1 +
 drivers/clocksource/timer-microchip-pit64b.c | 501 +++++++++++++++++++++++++++
 3 files changed, 508 insertions(+)
 create mode 100644 drivers/clocksource/timer-microchip-pit64b.c

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 5fdd76cb1768..eaadbc42ce4a 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -697,4 +697,10 @@ config INGENIC_TIMER
 	help
 	  Support for the timer/counter unit of the Ingenic JZ SoCs.
 
+config MICROCHIP_PIT64B
+	bool "Microchip PIT64B support"
+	depends on OF || COMPILE_TEST
+	help
+	  This option enables Microchip PIT64B timer.
+
 endmenu
diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index 4dfe4225ece7..713686faa549 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -88,3 +88,4 @@ obj-$(CONFIG_RISCV_TIMER)		+= timer-riscv.o
 obj-$(CONFIG_CSKY_MP_TIMER)		+= timer-mp-csky.o
 obj-$(CONFIG_GX6605S_TIMER)		+= timer-gx6605s.o
 obj-$(CONFIG_HYPERV_TIMER)		+= hyperv_timer.o
+obj-$(CONFIG_MICROCHIP_PIT64B)		+= timer-microchip-pit64b.o
diff --git a/drivers/clocksource/timer-microchip-pit64b.c b/drivers/clocksource/timer-microchip-pit64b.c
new file mode 100644
index 000000000000..293e1ab39729
--- /dev/null
+++ b/drivers/clocksource/timer-microchip-pit64b.c
@@ -0,0 +1,501 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * 64-bit Periodic Interval Timer driver
+ *
+ * Copyright (C) 2019 Microchip Technology Inc. and its subsidiaries
+ *
+ * Author: Claudiu Beznea <claudiu.beznea@microchip.com>
+ */
+
+#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_ONE_SHOT		(0)
+#define MCHP_PIT64B_MR_SGCLK		BIT(3)
+#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_LSBMASK		GENMASK_ULL(31, 0)
+#define MCHP_PIT64B_PRESCALER(p)	(MCHP_PIT64B_MR_PRES & ((p) << 8))
+#define MCHP_PIT64B_DEF_CS_FREQ		5000000UL	/* 5 MHz */
+#define MCHP_PIT64B_DEF_CE_FREQ		32768		/* 32 KHz */
+
+#define MCHP_PIT64B_NAME		"pit64b"
+
+/**
+ * struct mchp_pit64b_timer - PIT64B timer data structure
+ * @base: base address of PIT64B hardware block
+ * @pclk: PIT64B's peripheral clock
+ * @gclk: PIT64B's generic clock
+ * @cycles: timer's number of cycles
+ * @irq: PIT64B's Linux IRQ number
+ * @pres: prescaler value for the chosen clock
+ */
+struct mchp_pit64b_timer {
+	void __iomem	*base;
+	struct clk	*pclk;
+	struct clk	*gclk;
+	u64		cycles;
+	u32		irq;
+	u8		pres;
+};
+
+/**
+ * mchp_pit64b_clksrc - PIT64B clocksource data structure
+ * @timer: PIT64B timer
+ * @clksrc: clocksource
+ */
+struct mchp_pit64b_clksrc {
+	struct mchp_pit64b_timer	timer;
+	struct clocksource		clksrc;
+};
+
+#define clksrc_to_mchp_pit64b_timer(x) \
+	(&(container_of(x, struct mchp_pit64b_clksrc, clksrc))->timer)
+
+/**
+ * mchp_pit64b_clkevt - PIT64B clockevent data structure
+ * @timer: PIT64B timer
+ * @clkevt: clockevent
+ */
+struct mchp_pit64b_clkevt {
+	struct mchp_pit64b_timer	timer;
+	struct clock_event_device	clkevt;
+};
+
+#define clkevt_to_mchp_pit64b_timer(x) \
+	(&(container_of(x, struct mchp_pit64b_clkevt, clkevt))->timer)
+
+static void __iomem *mchp_pit64b_cs_base;
+
+static inline u64 mchp_pit64b_get_period(void __iomem *base)
+{
+	unsigned long	flags;
+	u32		low, high;
+
+	raw_local_irq_save(flags);
+	/*
+	 * When using a 64 bit period TLSB must be read first, followed by the
+	 * read of TMSB. This sequence generates an atomic read of the 64 bit
+	 * timer value whatever the lapse of time between the accesses.
+	 */
+	low = readl_relaxed(base + MCHP_PIT64B_TLSBR);
+	high = readl_relaxed(base + MCHP_PIT64B_TMSBR);
+	raw_local_irq_restore(flags);
+
+	return (((u64)high << 32) | low);
+}
+
+static inline void mchp_pit64b_reset(struct mchp_pit64b_timer *timer,
+				     u64 cycles, u32 mode)
+{
+	u32 low, high;
+
+	low = cycles & MCHP_PIT64B_LSBMASK;
+	high = cycles >> 32;
+
+	mode |= MCHP_PIT64B_PRESCALER(timer->pres);
+	if (timer->gclk)
+		mode |= MCHP_PIT64B_MR_SGCLK;
+
+	writel_relaxed(MCHP_PIT64B_CR_SWRST, timer->base + MCHP_PIT64B_CR);
+	writel_relaxed(mode, timer->base + MCHP_PIT64B_MR);
+	writel_relaxed(high, timer->base + MCHP_PIT64B_MSB_PR);
+	writel_relaxed(low, timer->base + MCHP_PIT64B_LSB_PR);
+	if (timer->irq) {
+		writel_relaxed(MCHP_PIT64B_IER_PERIOD,
+			       timer->base + MCHP_PIT64B_IER);
+	}
+	writel_relaxed(MCHP_PIT64B_CR_START, timer->base + MCHP_PIT64B_CR);
+}
+
+static u64 mchp_pit64b_clksrc_read(struct clocksource *cs)
+{
+	struct mchp_pit64b_timer *timer = clksrc_to_mchp_pit64b_timer(cs);
+
+	return mchp_pit64b_get_period(timer->base);
+}
+
+static u64 mchp_pit64b_sched_read_clk(void)
+{
+	return mchp_pit64b_get_period(mchp_pit64b_cs_base);
+}
+
+static int mchp_pit64b_clkevt_shutdown(struct clock_event_device *cedev)
+{
+	struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
+
+	writel_relaxed(MCHP_PIT64B_CR_SWRST, timer->base + MCHP_PIT64B_CR);
+
+	return 0;
+}
+
+static int mchp_pit64b_clkevt_set_periodic(struct clock_event_device *cedev)
+{
+	struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
+
+	mchp_pit64b_reset(timer, timer->cycles, MCHP_PIT64B_MR_CONT);
+
+	return 0;
+}
+
+static int mchp_pit64b_clkevt_set_oneshot(struct clock_event_device *cedev)
+{
+	struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
+
+	mchp_pit64b_reset(timer, timer->cycles, MCHP_PIT64B_MR_ONE_SHOT);
+
+	return 0;
+}
+
+static int mchp_pit64b_clkevt_set_next_event(unsigned long evt,
+					     struct clock_event_device *cedev)
+{
+	struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
+
+	mchp_pit64b_reset(timer, evt, MCHP_PIT64B_MR_ONE_SHOT);
+
+	return 0;
+}
+
+static void mchp_pit64b_clkevt_suspend(struct clock_event_device *cedev)
+{
+	struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
+
+	writel_relaxed(MCHP_PIT64B_CR_SWRST, timer->base + MCHP_PIT64B_CR);
+	if (timer->gclk)
+		clk_disable_unprepare(timer->gclk);
+	clk_disable_unprepare(timer->pclk);
+}
+
+static void mchp_pit64b_clkevt_resume(struct clock_event_device *cedev)
+{
+	struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
+	u32 mode = MCHP_PIT64B_MR_ONE_SHOT;
+
+	clk_prepare_enable(timer->pclk);
+	if (timer->gclk)
+		clk_prepare_enable(timer->gclk);
+
+	if (clockevent_state_periodic(cedev))
+		mode = MCHP_PIT64B_MR_CONT;
+
+	mchp_pit64b_reset(timer, timer->cycles, mode);
+}
+
+static irqreturn_t mchp_pit64b_interrupt(int irq, void *dev_id)
+{
+	struct mchp_pit64b_clkevt *irq_data = dev_id;
+
+	/* Need to clear the interrupt. */
+	readl_relaxed(irq_data->timer.base + MCHP_PIT64B_ISR);
+
+	irq_data->clkevt.event_handler(&irq_data->clkevt);
+
+	return IRQ_HANDLED;
+}
+
+static void __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;
+	}
+
+	/* Use the bigest prescaler if we didn't match one. */
+	if (*pres == MCHP_PIT64B_PRES_MAX)
+		*pres = MCHP_PIT64B_PRES_MAX - 1;
+}
+
+/**
+ * mchp_pit64b_pres_prepare - prepare PIT64B clocks and internal prescaler
+ *
+ * PIT64B timer may be fed by gclk or pclk. When gclk is used its rate has to
+ * be at least 3 times lower that pclk's rate. pclk rate is fixed, gclk rate
+ * could be changed via clock APIs. The chosen clock (pclk or gclk) could be
+ * divided by the internal PIT64B's divider.
+ *
+ * This function, first tries to use GCLK by requesting the desired rate from
+ * PMC and then using the internal PIT64B prescaller, if any, to reach the
+ * requested rate. If PCLK/GCLK < 3 (condition requested by PIT64B hardware)
+ * then the function falls back on using PCLK as clock source for PIT64B timer
+ * choosing the highest prescaler in case it doesn't locate one to match the
+ * requested frequency.
+ *
+ * Below is presented the PIT64B block in relation with PMC:
+ *
+ *                                PIT64B
+ *  PMC             +------------------------------------+
+ * +----+           |   +-----+                          |
+ * |    |-->gclk -->|-->|     |    +---------+  +-----+  |
+ * |    |           |   | MUX |--->| Divider |->|timer|  |
+ * |    |-->pclk -->|-->|     |    +---------+  +-----+  |
+ * +----+           |   +-----+                          |
+ *                  |      ^                             |
+ *                  |     sel                            |
+ *                  +------------------------------------+
+ *
+ * Where:
+ *	- gclk rate <= pclk rate/3
+ *	- gclk rate could be requested from PMC
+ *	- pclk rate is fixed (cannot be requested from PMC)
+ */
+static int __init mchp_pit64b_pres_prepare(struct mchp_pit64b_timer *timer,
+					   unsigned long max_rate)
+{
+	unsigned long pclk_rate, diff = 0, best_diff = ULONG_MAX;
+	long gclk_round = 0;
+	u32 pres, best_pres = 0;
+
+	pclk_rate = clk_get_rate(timer->pclk);
+	if (!pclk_rate)
+		return -EINVAL;
+
+	/* Try using GCLK. */
+	gclk_round = clk_round_rate(timer->gclk, max_rate);
+	if (gclk_round < 0)
+		goto pclk;
+
+	if (pclk_rate / gclk_round < 3)
+		goto pclk;
+
+	mchp_pit64b_pres_compute(&pres, gclk_round, max_rate);
+	best_diff = abs(gclk_round / (pres + 1) - max_rate);
+	best_pres = pres;
+
+	if (!best_diff)
+		goto done;
+
+pclk:
+	/* Check if requested rate could be obtained using PCLK. */
+	mchp_pit64b_pres_compute(&pres, pclk_rate, max_rate);
+	diff = abs(pclk_rate / (pres + 1) - max_rate);
+
+	if (best_diff > diff) {
+		/* Use PCLK. */
+		timer->gclk = NULL;
+		best_pres = pres;
+	} else {
+		/* Use GCLK. */
+		clk_set_rate(timer->gclk, gclk_round);
+	}
+
+done:
+	timer->pres = best_pres;
+	pr_info("PIT64B: using clk=%s with prescaler %u, freq=%lu [Hz]\n",
+		timer->gclk ? "gclk" : "pclk", timer->pres,
+		timer->gclk ? gclk_round / (timer->pres + 1)
+			    : pclk_rate / (timer->pres + 1));
+
+	return 0;
+}
+
+static int __init mchp_pit64b_timer_init(struct device_node *node,
+					 struct mchp_pit64b_timer *timer,
+					 u32 freq, bool is_clkevt)
+{
+	int ret;
+
+	timer->pclk = of_clk_get_by_name(node, "pclk");
+	if (IS_ERR(timer->pclk))
+		return PTR_ERR(timer->pclk);
+
+	timer->gclk = of_clk_get_by_name(node, "gclk");
+	if (IS_ERR(timer->gclk))
+		return PTR_ERR(timer->gclk);
+
+	timer->base = of_iomap(node, 0);
+	if (!timer->base)
+		return -ENXIO;
+
+	if (is_clkevt) {
+		timer->irq = irq_of_parse_and_map(node, 0);
+		if (!timer->irq) {
+			ret = -ENODEV;
+			goto io_unmap;
+		}
+	}
+
+	ret = mchp_pit64b_pres_prepare(timer, freq);
+	if (ret)
+		goto irq_unmap;
+
+	ret = clk_prepare_enable(timer->pclk);
+	if (ret)
+		goto irq_unmap;
+
+	if (timer->gclk) {
+		ret = clk_prepare_enable(timer->gclk);
+		if (ret)
+			goto pclk_unprepare;
+	}
+
+	return 0;
+
+pclk_unprepare:
+	clk_disable_unprepare(timer->pclk);
+irq_unmap:
+	irq_dispose_mapping(timer->irq);
+io_unmap:
+	iounmap(timer->base);
+
+	return ret;
+}
+
+static void __init mchp_pit64b_timer_cleanup(struct mchp_pit64b_timer *timer)
+{
+	if (timer->gclk)
+		clk_disable_unprepare(timer->gclk);
+	clk_disable_unprepare(timer->pclk);
+	irq_dispose_mapping(timer->irq);
+	iounmap(timer->base);
+}
+
+static int __init mchp_pit64b_dt_init_clksrc(struct device_node *node)
+{
+	struct mchp_pit64b_clksrc *cs;
+	unsigned long clk_rate;
+	int ret;
+
+	cs = kzalloc(sizeof(*cs), GFP_KERNEL);
+	if (!cs)
+		return -ENOMEM;
+
+	ret = mchp_pit64b_timer_init(node, &cs->timer, MCHP_PIT64B_DEF_CS_FREQ,
+				     false);
+	if (ret)
+		goto free;
+
+	if (cs->timer.gclk)
+		clk_rate = clk_get_rate(cs->timer.gclk);
+	else
+		clk_rate = clk_get_rate(cs->timer.pclk);
+
+	clk_rate = clk_rate / (cs->timer.pres + 1);
+	cs->timer.cycles = ULLONG_MAX;
+	mchp_pit64b_reset(&cs->timer, cs->timer.cycles, MCHP_PIT64B_MR_CONT);
+
+	cs->clksrc.name = MCHP_PIT64B_NAME;
+	cs->clksrc.mask = CLOCKSOURCE_MASK(64);
+	cs->clksrc.flags = CLOCK_SOURCE_IS_CONTINUOUS;
+	cs->clksrc.rating = 210;
+	cs->clksrc.read = mchp_pit64b_clksrc_read;
+
+	ret = clocksource_register_hz(&cs->clksrc, clk_rate);
+	if (ret) {
+		pr_debug("clksrc: Failed to register PIT64B clocksource!\n");
+		goto timer_cleanup;
+	}
+
+	mchp_pit64b_cs_base = cs->timer.base;
+	sched_clock_register(mchp_pit64b_sched_read_clk, 64, clk_rate);
+
+	return 0;
+
+timer_cleanup:
+	mchp_pit64b_timer_cleanup(&cs->timer);
+free:
+	kfree(cs);
+	return ret;
+}
+
+static int __init mchp_pit64b_dt_init_clkevt(struct device_node *node)
+{
+	struct mchp_pit64b_clkevt *ce;
+	unsigned long clk_rate;
+	int ret;
+
+	ce = kzalloc(sizeof(*ce), GFP_KERNEL);
+	if (!ce)
+		return -ENOMEM;
+
+	ret = mchp_pit64b_timer_init(node, &ce->timer, MCHP_PIT64B_DEF_CE_FREQ,
+				     true);
+	if (ret)
+		goto free;
+
+	if (ce->timer.gclk)
+		clk_rate = clk_get_rate(ce->timer.gclk);
+	else
+		clk_rate = clk_get_rate(ce->timer.pclk);
+
+	clk_rate = clk_rate / (ce->timer.pres + 1);
+	ce->timer.cycles = DIV_ROUND_CLOSEST(clk_rate, HZ);
+
+	ce->clkevt.name = MCHP_PIT64B_NAME;
+	ce->clkevt.features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_PERIODIC;
+	ce->clkevt.rating = 150;
+	ce->clkevt.set_state_shutdown = mchp_pit64b_clkevt_shutdown;
+	ce->clkevt.set_state_periodic = mchp_pit64b_clkevt_set_periodic;
+	ce->clkevt.set_state_oneshot = mchp_pit64b_clkevt_set_oneshot;
+	ce->clkevt.set_next_event = mchp_pit64b_clkevt_set_next_event;
+	ce->clkevt.suspend = mchp_pit64b_clkevt_suspend;
+	ce->clkevt.resume = mchp_pit64b_clkevt_resume;
+	ce->clkevt.cpumask = cpumask_of(0);
+	ce->clkevt.irq = ce->timer.irq;
+
+	ret = request_irq(ce->timer.irq, mchp_pit64b_interrupt, IRQF_TIMER,
+			  "pit64b_tick", ce);
+	if (ret) {
+		pr_debug("clkevt: Failed to setup PIT64B IRQ\n");
+		goto timer_cleanup;
+	}
+
+	clockevents_config_and_register(&ce->clkevt, clk_rate, 1, ULONG_MAX);
+
+	return 0;
+
+timer_cleanup:
+	mchp_pit64b_timer_cleanup(&ce->timer);
+free:
+	kfree(ce);
+	return ret;
+}
+
+static int __init mchp_pit64b_dt_init(struct device_node *node)
+{
+	static int inits;
+
+	switch (inits++) {
+	case 0:
+		/* 1st request, register clockevent. */
+		return mchp_pit64b_dt_init_clkevt(node);
+	case 1:
+		/* 2nd request, register clocksource. */
+		return mchp_pit64b_dt_init_clksrc(node);
+	}
+
+	/* The rest, don't care. */
+	return -EINVAL;
+}
+
+TIMER_OF_DECLARE(mchp_pit64b, "microchip,sam9x60-pit64b", mchp_pit64b_dt_init);
-- 
2.7.4

Re: [PATCH v3 2/2] clocksource/drivers/timer-microchip-pit64b: add Microchip PIT64B support

[Daniel Lezcano]

On 04/12/2019 15:42, Claudiu Beznea wrote:
> 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.
> The driver uses PIT64B timer for clocksource or clockevent. First
> requested timer would be registered as clockevent, second one would be
> registered as clocksource. 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 <claudiu.beznea@microchip.com>
> ---
> 
> Changes in v3:
> - rework data structures:
> 	- timer related data structure is called now mchp_pit64b_timer embedding
> 	  base iomem, clocks, interrupt, prescaler value
> 	- introduced struct mchp_pit64b_clksrc and struct mchp_pit64b_clkevt
> 	  instead of mchp_pit64b_clksrc_data and mchp_pit64b_clkevt_data
> 	- use container_of() to retrieve mchp_pit64b_timer objects on
> 	  clocksource/clockevent specific APIs
> 	- document data structures
> - use raw_local_irq_save()/raw_local_irq_restore() when reading
>   MCHP_PIT64B_TLSBR and MCHP_PIT64B_TMSBR in mchp_pit64b_get_period()
> - get rid of mchp_pit64b_read(), mchp_pit64b_write() and use instead
>   readl_relaxed(), writel_relaxed()
> - get rid of mchp_pit64b_set_period() and inlined its instructions in
>   mchp_pit64b_reset()
> - mchp_pit64b_reset() gets now as arguments an object of type
>   struct mchp_pit64b_timer, cycles to program and mode
> - remove static struct clocksource mchp_pit64b_clksrc and
>   static struct clock_event_device mchp_pit64b_clkevt and instead allocate
>   and fill them in mchp_pit64b_dt_init_clksrc() and
>   mchp_pit64b_dt_init_clkevt()
> - call mchp_pit64b_reset() in mchp_pit64b_clkevt_set_next_event() and
>   program clockevent timer with SMOD=0; if SMOD=1 the timer's period could
>   be reprogrammed also if writting TLSB, TMSB if it is running. In cases
>   were its period expired START bit still has to be set in control register.
>   In case the programming sequence is like in v2, with SMOD=1:
> 	- program MSB_PR
> 	- program LSB_PR
> 	- program START bit in control register
>   for short programmed periods we may start the timer twice with this
>   programming sequence, 1st time after LSB_PR is updated (and due to SMOD=1),
>   2nd time after programming START bit in control register and in case
>   programmed period already expire
> - simplify mchp_pit64b_interrupt() by just reading ISR register, to clear the
>   received interrupt, and just call irq_data->clkevt->event_handler(irq_data->clkevt);
> - in mchp_pit64b_pres_compute() chose the bigest prescaler in case a good
>   one not found
> - document mchp_pit64b_pres_prepare() and simplified it a bit
> - enforce gclk as mandatory
> - introduce mchp_pit64b_timer_init() and mchp_pit64b_timer_cleanup()
> - keep the clocksource timer base address in a mchp_pit64b_cs_base variable so
>   that it could be used by mchp_pit64b_sched_read_clk()
> - rework mchp_pit64b_dt_init() and return -EINVAL in case it was called
>   more than two times: one for initialization of clockevent, one for
>   initialization of clocksource
> - introduce MCHP_PIT64B_MR_ONE_SHOT define
> - move the new lines introduced in Makefile and Kconfig at the end of files
> - collect Rob's Reviewed-by tag on patch 1/2
> - review the commit message of patch 2/2
> 
> Changes in v2:
> - remove clock-frequency DT binding and hardcoded it in the driver
> - initialize best_pres variable in mchp_pit64b_pres_prepare()
> - remove MCHP_PIT64B_DEF_FREQ 
> - get rid of patches 3-5 from v1 [1] since there is no entry in MAINTAINERS file
>   for this entry. It was removed in
>   commit 44015a8181a5 ("MAINTAINERS: at91: remove the TC entry")
> 
> [1] https://lore.kernel.org/lkml/1552580772-8499-1-git-send-email-claudiu.beznea@microchip.com/
> 
>  drivers/clocksource/Kconfig                  |   6 +
>  drivers/clocksource/Makefile                 |   1 +
>  drivers/clocksource/timer-microchip-pit64b.c | 501 +++++++++++++++++++++++++++
>  3 files changed, 508 insertions(+)
>  create mode 100644 drivers/clocksource/timer-microchip-pit64b.c
> 
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index 5fdd76cb1768..eaadbc42ce4a 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -697,4 +697,10 @@ config INGENIC_TIMER
>  	help
>  	  Support for the timer/counter unit of the Ingenic JZ SoCs.
>  
> +config MICROCHIP_PIT64B
> +	bool "Microchip PIT64B support"
> +	depends on OF || COMPILE_TEST
> +	help
> +	  This option enables Microchip PIT64B timer.
> +
>  endmenu
> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> index 4dfe4225ece7..713686faa549 100644
> --- a/drivers/clocksource/Makefile
> +++ b/drivers/clocksource/Makefile
> @@ -88,3 +88,4 @@ obj-$(CONFIG_RISCV_TIMER)		+= timer-riscv.o
>  obj-$(CONFIG_CSKY_MP_TIMER)		+= timer-mp-csky.o
>  obj-$(CONFIG_GX6605S_TIMER)		+= timer-gx6605s.o
>  obj-$(CONFIG_HYPERV_TIMER)		+= hyperv_timer.o
> +obj-$(CONFIG_MICROCHIP_PIT64B)		+= timer-microchip-pit64b.o
> diff --git a/drivers/clocksource/timer-microchip-pit64b.c b/drivers/clocksource/timer-microchip-pit64b.c
> new file mode 100644
> index 000000000000..293e1ab39729
> --- /dev/null
> +++ b/drivers/clocksource/timer-microchip-pit64b.c
> @@ -0,0 +1,501 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * 64-bit Periodic Interval Timer driver
> + *
> + * Copyright (C) 2019 Microchip Technology Inc. and its subsidiaries
> + *
> + * Author: Claudiu Beznea <claudiu.beznea@microchip.com>
> + */
> +
> +#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_ONE_SHOT		(0)
> +#define MCHP_PIT64B_MR_SGCLK		BIT(3)
> +#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_LSBMASK		GENMASK_ULL(31, 0)
> +#define MCHP_PIT64B_PRESCALER(p)	(MCHP_PIT64B_MR_PRES & ((p) << 8))
> +#define MCHP_PIT64B_DEF_CS_FREQ		5000000UL	/* 5 MHz */
> +#define MCHP_PIT64B_DEF_CE_FREQ		32768		/* 32 KHz */
> +
> +#define MCHP_PIT64B_NAME		"pit64b"
> +
> +/**
> + * struct mchp_pit64b_timer - PIT64B timer data structure
> + * @base: base address of PIT64B hardware block
> + * @pclk: PIT64B's peripheral clock
> + * @gclk: PIT64B's generic clock
> + * @cycles: timer's number of cycles
> + * @irq: PIT64B's Linux IRQ number
> + * @pres: prescaler value for the chosen clock
> + */
> +struct mchp_pit64b_timer {
> +	void __iomem	*base;
> +	struct clk	*pclk;
> +	struct clk	*gclk;
> +	u64		cycles;
> +	u32		irq;

irq is not needed, a local variable is enough to setup the timer.


> +	u8		pres;
> +};

The field pres and cycles are needed to reset the clockevent, is it
really mandatory to set them again and again from the value stored?

> +
> +/**
> + * mchp_pit64b_clksrc - PIT64B clocksource data structure
> + * @timer: PIT64B timer
> + * @clksrc: clocksource
> + */
> +struct mchp_pit64b_clksrc {
> +	struct mchp_pit64b_timer	timer;
> +	struct clocksource		clksrc;
> +};

clksrc would be not needed here if you use the function:
	clocksource_mmio_init()

> +#define clksrc_to_mchp_pit64b_timer(x) \
> +	(&(container_of(x, struct mchp_pit64b_clksrc, clksrc))->timer)

No dereference should happen here. We should end up with a single structure:

struct mchp_pit64b_timer {
	void *__iomem			*base;
	struct clk			*pclk;
	struct clk			*gclk;
	struct clock_event_device	clkevt
};

> + * mchp_pit64b_clkevt - PIT64B clockevent data structure
> + * @timer: PIT64B timer
> + * @clkevt: clockevent
> + */
> +struct mchp_pit64b_clkevt {
> +	struct mchp_pit64b_timer	timer;
> +	struct clock_event_device	clkevt;
> +};
> +
> +#define clkevt_to_mchp_pit64b_timer(x) \
> +	(&(container_of(x, struct mchp_pit64b_clkevt, clkevt))->timer)

Same comment.

> +> +static void __iomem *mchp_pit64b_cs_base;
>
> +static inline u64 mchp_pit64b_get_period(void __iomem *base)

The 'get_period' name is confusing. Can you replace that by 'get_counter'?

Also, the 'high' part change may be checked, like:

https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/tree/drivers/clocksource/timer-imx-sysctr.c?h=bleeding-edge#n51

You should consider if using only the first 32bits wouldn't be enough
(max duration before wrapping up). Using the 64bits here has a
significant impact on the performances. Up to you to decide.

> +{
> +	unsigned long	flags;
> +	u32		low, high;
> +
> +	raw_local_irq_save(flags);
> +	/*
> +	 * When using a 64 bit period TLSB must be read first, followed by the
> +	 * read of TMSB. This sequence generates an atomic read of the 64 bit
> +	 * timer value whatever the lapse of time between the accesses.
> +	 */
> +	low = readl_relaxed(base + MCHP_PIT64B_TLSBR);
> +	high = readl_relaxed(base + MCHP_PIT64B_TMSBR);

Add line for clarity.

> +	raw_local_irq_restore(flags);
> +
> +	return (((u64)high << 32) | low);
> +}
> +
> +static inline void mchp_pit64b_reset(struct mchp_pit64b_timer *timer,
> +				     u64 cycles, u32 mode)
> +{
> +	u32 low, high;
> +
> +	low = cycles & MCHP_PIT64B_LSBMASK;
> +	high = cycles >> 32;
> +
> +	mode |= MCHP_PIT64B_PRESCALER(timer->pres);
> +	if (timer->gclk)
> +		mode |= MCHP_PIT64B_MR_SGCLK;

Why not pre-compute 'mode', make it a field of the timer struct and
change the value at init time and in set_periodic and set_oneshot?

> +	writel_relaxed(MCHP_PIT64B_CR_SWRST, timer->base + MCHP_PIT64B_CR);
> +	writel_relaxed(mode, timer->base + MCHP_PIT64B_MR);
> +	writel_relaxed(high, timer->base + MCHP_PIT64B_MSB_PR);
> +	writel_relaxed(low, timer->base + MCHP_PIT64B_LSB_PR);
> +	if (timer->irq) {

Clocksource reset is only needed at init time, it can be done separetely
and this function will be called for the clockevent only, hence the
check won't be necessary.

> +		writel_relaxed(MCHP_PIT64B_IER_PERIOD,
> +			       timer->base + MCHP_PIT64B_IER);
> +	}
> +	writel_relaxed(MCHP_PIT64B_CR_START, timer->base + MCHP_PIT64B_CR);
> +}
> +
> +static u64 mchp_pit64b_clksrc_read(struct clocksource *cs)
> +{
> +	struct mchp_pit64b_timer *timer = clksrc_to_mchp_pit64b_timer(cs);
> +
> +	return mchp_pit64b_get_period(timer->base);
> +}
> +
> +static u64 mchp_pit64b_sched_read_clk(void)
> +{
> +	return mchp_pit64b_get_period(mchp_pit64b_cs_base);
> +}
> +
> +static int mchp_pit64b_clkevt_shutdown(struct clock_event_device *cedev)
> +{
> +	struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
> +
> +	writel_relaxed(MCHP_PIT64B_CR_SWRST, timer->base + MCHP_PIT64B_CR);
> +
> +	return 0;
> +}
> +
> +static int mchp_pit64b_clkevt_set_periodic(struct clock_event_device *cedev)
> +{
> +	struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
> +
> +	mchp_pit64b_reset(timer, timer->cycles, MCHP_PIT64B_MR_CONT);
> +
> +	return 0;
> +}
> +
> +static int mchp_pit64b_clkevt_set_oneshot(struct clock_event_device *cedev)
> +{
> +	struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
> +
> +	mchp_pit64b_reset(timer, timer->cycles, MCHP_PIT64B_MR_ONE_SHOT);
> +
> +	return 0;
> +}
> +
> +static int mchp_pit64b_clkevt_set_next_event(unsigned long evt,
> +					     struct clock_event_device *cedev)
> +{
> +	struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
> +
> +	mchp_pit64b_reset(timer, evt, MCHP_PIT64B_MR_ONE_SHOT);
> +
> +	return 0;
> +}
> +
> +static void mchp_pit64b_clkevt_suspend(struct clock_event_device *cedev)
> +{
> +	struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
> +
> +	writel_relaxed(MCHP_PIT64B_CR_SWRST, timer->base + MCHP_PIT64B_CR);
> +	if (timer->gclk)
> +		clk_disable_unprepare(timer->gclk);
> +	clk_disable_unprepare(timer->pclk);
> +}
> +
> +static void mchp_pit64b_clkevt_resume(struct clock_event_device *cedev)
> +{
> +	struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
> +	u32 mode = MCHP_PIT64B_MR_ONE_SHOT;
> +
> +	clk_prepare_enable(timer->pclk);
> +	if (timer->gclk)
> +		clk_prepare_enable(timer->gclk);
> +
> +	if (clockevent_state_periodic(cedev))
> +		mode = MCHP_PIT64B_MR_CONT;
> +
> +	mchp_pit64b_reset(timer, timer->cycles, mode);
> +}
> +
> +static irqreturn_t mchp_pit64b_interrupt(int irq, void *dev_id)
> +{
> +	struct mchp_pit64b_clkevt *irq_data = dev_id;
> +
> +	/* Need to clear the interrupt. */
> +	readl_relaxed(irq_data->timer.base + MCHP_PIT64B_ISR);
> +
> +	irq_data->clkevt.event_handler(&irq_data->clkevt);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static void __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;
> +	}
> +
> +	/* Use the bigest prescaler if we didn't match one. */
> +	if (*pres == MCHP_PIT64B_PRES_MAX)
> +		*pres = MCHP_PIT64B_PRES_MAX - 1;
> +}
> +
> +/**
> + * mchp_pit64b_pres_prepare - prepare PIT64B clocks and internal prescaler
> + *
> + * PIT64B timer may be fed by gclk or pclk. When gclk is used its rate has to
> + * be at least 3 times lower that pclk's rate. pclk rate is fixed, gclk rate
> + * could be changed via clock APIs. The chosen clock (pclk or gclk) could be
> + * divided by the internal PIT64B's divider.
> + *
> + * This function, first tries to use GCLK by requesting the desired rate from
> + * PMC and then using the internal PIT64B prescaller, if any, to reach the
> + * requested rate. If PCLK/GCLK < 3 (condition requested by PIT64B hardware)
> + * then the function falls back on using PCLK as clock source for PIT64B timer
> + * choosing the highest prescaler in case it doesn't locate one to match the
> + * requested frequency.
> + *
> + * Below is presented the PIT64B block in relation with PMC:
> + *
> + *                                PIT64B
> + *  PMC             +------------------------------------+
> + * +----+           |   +-----+                          |
> + * |    |-->gclk -->|-->|     |    +---------+  +-----+  |
> + * |    |           |   | MUX |--->| Divider |->|timer|  |
> + * |    |-->pclk -->|-->|     |    +---------+  +-----+  |
> + * +----+           |   +-----+                          |
> + *                  |      ^                             |
> + *                  |     sel                            |
> + *                  +------------------------------------+
> + *
> + * Where:
> + *	- gclk rate <= pclk rate/3
> + *	- gclk rate could be requested from PMC
> + *	- pclk rate is fixed (cannot be requested from PMC)
> + */
> +static int __init mchp_pit64b_pres_prepare(struct mchp_pit64b_timer *timer,
> +					   unsigned long max_rate)
> +{
> +	unsigned long pclk_rate, diff = 0, best_diff = ULONG_MAX;
> +	long gclk_round = 0;
> +	u32 pres, best_pres = 0;
> +
> +	pclk_rate = clk_get_rate(timer->pclk);
> +	if (!pclk_rate)
> +		return -EINVAL;
> +
> +	/* Try using GCLK. */
> +	gclk_round = clk_round_rate(timer->gclk, max_rate);
> +	if (gclk_round < 0)
> +		goto pclk;
> +
> +	if (pclk_rate / gclk_round < 3)
> +		goto pclk;
> +
> +	mchp_pit64b_pres_compute(&pres, gclk_round, max_rate);
> +	best_diff = abs(gclk_round / (pres + 1) - max_rate);
> +	best_pres = pres;
> +
> +	if (!best_diff)
> +		goto done;
> +
> +pclk:
> +	/* Check if requested rate could be obtained using PCLK. */
> +	mchp_pit64b_pres_compute(&pres, pclk_rate, max_rate);
> +	diff = abs(pclk_rate / (pres + 1) - max_rate);
> +
> +	if (best_diff > diff) {
> +		/* Use PCLK. */
> +		timer->gclk = NULL;
> +		best_pres = pres;
> +	} else {
> +		/* Use GCLK. */
> +		clk_set_rate(timer->gclk, gclk_round);
> +	}
> +
> +done:
> +	timer->pres = best_pres;
> +	pr_info("PIT64B: using clk=%s with prescaler %u, freq=%lu [Hz]\n",
> +		timer->gclk ? "gclk" : "pclk", timer->pres,
> +		timer->gclk ? gclk_round / (timer->pres + 1)
> +			    : pclk_rate / (timer->pres + 1));
> +
> +	return 0;
> +}
> +
> +static int __init mchp_pit64b_timer_init(struct device_node *node,
> +					 struct mchp_pit64b_timer *timer,
> +					 u32 freq, bool is_clkevt)
> +{
> +	int ret;
> +
> +	timer->pclk = of_clk_get_by_name(node, "pclk");
> +	if (IS_ERR(timer->pclk))
> +		return PTR_ERR(timer->pclk);
> +
> +	timer->gclk = of_clk_get_by_name(node, "gclk");
> +	if (IS_ERR(timer->gclk))
> +		return PTR_ERR(timer->gclk);
> +
> +	timer->base = of_iomap(node, 0);
> +	if (!timer->base)
> +		return -ENXIO;
> +
> +	if (is_clkevt) {
> +		timer->irq = irq_of_parse_and_map(node, 0);
> +		if (!timer->irq) {
> +			ret = -ENODEV;
> +			goto io_unmap;
> +		}
> +	}
> +
> +	ret = mchp_pit64b_pres_prepare(timer, freq);
> +	if (ret)
> +		goto irq_unmap;
> +
> +	ret = clk_prepare_enable(timer->pclk);
> +	if (ret)
> +		goto irq_unmap;
> +
> +	if (timer->gclk) {
> +		ret = clk_prepare_enable(timer->gclk);
> +		if (ret)
> +			goto pclk_unprepare;
> +	}
> +
> +	return 0;
> +
> +pclk_unprepare:
> +	clk_disable_unprepare(timer->pclk);
> +irq_unmap:
> +	irq_dispose_mapping(timer->irq);
> +io_unmap:
> +	iounmap(timer->base);
> +
> +	return ret;
> +}
> +
> +static void __init mchp_pit64b_timer_cleanup(struct mchp_pit64b_timer *timer)
> +{
> +	if (timer->gclk)
> +		clk_disable_unprepare(timer->gclk);
> +	clk_disable_unprepare(timer->pclk);
> +	irq_dispose_mapping(timer->irq);
> +	iounmap(timer->base);
> +}
> +
> +static int __init mchp_pit64b_dt_init_clksrc(struct device_node *node)
> +{
> +	struct mchp_pit64b_clksrc *cs;
> +	unsigned long clk_rate;
> +	int ret;
> +
> +	cs = kzalloc(sizeof(*cs), GFP_KERNEL);
> +	if (!cs)
> +		return -ENOMEM;
> +
> +	ret = mchp_pit64b_timer_init(node, &cs->timer, MCHP_PIT64B_DEF_CS_FREQ,
> +				     false);
> +	if (ret)
> +		goto free;
> +
> +	if (cs->timer.gclk)
> +		clk_rate = clk_get_rate(cs->timer.gclk);
> +	else
> +		clk_rate = clk_get_rate(cs->timer.pclk);
> +
> +	clk_rate = clk_rate / (cs->timer.pres + 1);
> +	cs->timer.cycles = ULLONG_MAX;
> +	mchp_pit64b_reset(&cs->timer, cs->timer.cycles, MCHP_PIT64B_MR_CONT);
> +
> +	cs->clksrc.name = MCHP_PIT64B_NAME;
> +	cs->clksrc.mask = CLOCKSOURCE_MASK(64);
> +	cs->clksrc.flags = CLOCK_SOURCE_IS_CONTINUOUS;
> +	cs->clksrc.rating = 210;
> +	cs->clksrc.read = mchp_pit64b_clksrc_read;
> +
> +	ret = clocksource_register_hz(&cs->clksrc, clk_rate);
> +	if (ret) {
> +		pr_debug("clksrc: Failed to register PIT64B clocksource!\n");
> +		goto timer_cleanup;
> +	}
> +
> +	mchp_pit64b_cs_base = cs->timer.base;
> +	sched_clock_register(mchp_pit64b_sched_read_clk, 64, clk_rate);
> +
> +	return 0;
> +
> +timer_cleanup:
> +	mchp_pit64b_timer_cleanup(&cs->timer);
> +free:
> +	kfree(cs);
> +	return ret;
> +}
> +
> +static int __init mchp_pit64b_dt_init_clkevt(struct device_node *node)
> +{
> +	struct mchp_pit64b_clkevt *ce;
> +	unsigned long clk_rate;
> +	int ret;
> +
> +	ce = kzalloc(sizeof(*ce), GFP_KERNEL);
> +	if (!ce)
> +		return -ENOMEM;
> +
> +	ret = mchp_pit64b_timer_init(node, &ce->timer, MCHP_PIT64B_DEF_CE_FREQ,
> +				     true);
> +	if (ret)
> +		goto free;
> +
> +	if (ce->timer.gclk)
> +		clk_rate = clk_get_rate(ce->timer.gclk);
> +	else
> +		clk_rate = clk_get_rate(ce->timer.pclk);
> +
> +	clk_rate = clk_rate / (ce->timer.pres + 1);
> +	ce->timer.cycles = DIV_ROUND_CLOSEST(clk_rate, HZ);
> +
> +	ce->clkevt.name = MCHP_PIT64B_NAME;
> +	ce->clkevt.features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_PERIODIC;
> +	ce->clkevt.rating = 150;
> +	ce->clkevt.set_state_shutdown = mchp_pit64b_clkevt_shutdown;
> +	ce->clkevt.set_state_periodic = mchp_pit64b_clkevt_set_periodic;
> +	ce->clkevt.set_state_oneshot = mchp_pit64b_clkevt_set_oneshot;
> +	ce->clkevt.set_next_event = mchp_pit64b_clkevt_set_next_event;
> +	ce->clkevt.suspend = mchp_pit64b_clkevt_suspend;
> +	ce->clkevt.resume = mchp_pit64b_clkevt_resume;
> +	ce->clkevt.cpumask = cpumask_of(0);
> +	ce->clkevt.irq = ce->timer.irq;
> +
> +	ret = request_irq(ce->timer.irq, mchp_pit64b_interrupt, IRQF_TIMER,
> +			  "pit64b_tick", ce);
> +	if (ret) {
> +		pr_debug("clkevt: Failed to setup PIT64B IRQ\n");
> +		goto timer_cleanup;
> +	}
> +
> +	clockevents_config_and_register(&ce->clkevt, clk_rate, 1, ULONG_MAX);
> +
> +	return 0;
> +
> +timer_cleanup:
> +	mchp_pit64b_timer_cleanup(&ce->timer);
> +free:
> +	kfree(ce);
> +	return ret;
> +}
> +
> +static int __init mchp_pit64b_dt_init(struct device_node *node)
> +{
> +	static int inits;
> +
> +	switch (inits++) {
> +	case 0:
> +		/* 1st request, register clockevent. */
> +		return mchp_pit64b_dt_init_clkevt(node);
> +	case 1:
> +		/* 2nd request, register clocksource. */
> +		return mchp_pit64b_dt_init_clksrc(node);
> +	}
> +
> +	/* The rest, don't care. */
> +	return -EINVAL;
> +}
> +
> +TIMER_OF_DECLARE(mchp_pit64b, "microchip,sam9x60-pit64b", mchp_pit64b_dt_init);
> 


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Re: [PATCH v3 2/2] clocksource/drivers/timer-microchip-pit64b: add Microchip PIT64B support

[Claudiu.Beznea]

On 09.12.2019 19:04, Daniel Lezcano wrote:
> On 04/12/2019 15:42, Claudiu Beznea wrote:
>> 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.
>> The driver uses PIT64B timer for clocksource or clockevent. First
>> requested timer would be registered as clockevent, second one would be
>> registered as clocksource. 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 <claudiu.beznea@microchip.com>
>> ---
>>
>> Changes in v3:
>> - rework data structures:
>>       - timer related data structure is called now mchp_pit64b_timer embedding
>>         base iomem, clocks, interrupt, prescaler value
>>       - introduced struct mchp_pit64b_clksrc and struct mchp_pit64b_clkevt
>>         instead of mchp_pit64b_clksrc_data and mchp_pit64b_clkevt_data
>>       - use container_of() to retrieve mchp_pit64b_timer objects on
>>         clocksource/clockevent specific APIs
>>       - document data structures
>> - use raw_local_irq_save()/raw_local_irq_restore() when reading
>>   MCHP_PIT64B_TLSBR and MCHP_PIT64B_TMSBR in mchp_pit64b_get_period()
>> - get rid of mchp_pit64b_read(), mchp_pit64b_write() and use instead
>>   readl_relaxed(), writel_relaxed()
>> - get rid of mchp_pit64b_set_period() and inlined its instructions in
>>   mchp_pit64b_reset()
>> - mchp_pit64b_reset() gets now as arguments an object of type
>>   struct mchp_pit64b_timer, cycles to program and mode
>> - remove static struct clocksource mchp_pit64b_clksrc and
>>   static struct clock_event_device mchp_pit64b_clkevt and instead allocate
>>   and fill them in mchp_pit64b_dt_init_clksrc() and
>>   mchp_pit64b_dt_init_clkevt()
>> - call mchp_pit64b_reset() in mchp_pit64b_clkevt_set_next_event() and
>>   program clockevent timer with SMOD=0; if SMOD=1 the timer's period could
>>   be reprogrammed also if writting TLSB, TMSB if it is running. In cases
>>   were its period expired START bit still has to be set in control register.
>>   In case the programming sequence is like in v2, with SMOD=1:
>>       - program MSB_PR
>>       - program LSB_PR
>>       - program START bit in control register
>>   for short programmed periods we may start the timer twice with this
>>   programming sequence, 1st time after LSB_PR is updated (and due to SMOD=1),
>>   2nd time after programming START bit in control register and in case
>>   programmed period already expire
>> - simplify mchp_pit64b_interrupt() by just reading ISR register, to clear the
>>   received interrupt, and just call irq_data->clkevt->event_handler(irq_data->clkevt);
>> - in mchp_pit64b_pres_compute() chose the bigest prescaler in case a good
>>   one not found
>> - document mchp_pit64b_pres_prepare() and simplified it a bit
>> - enforce gclk as mandatory
>> - introduce mchp_pit64b_timer_init() and mchp_pit64b_timer_cleanup()
>> - keep the clocksource timer base address in a mchp_pit64b_cs_base variable so
>>   that it could be used by mchp_pit64b_sched_read_clk()
>> - rework mchp_pit64b_dt_init() and return -EINVAL in case it was called
>>   more than two times: one for initialization of clockevent, one for
>>   initialization of clocksource
>> - introduce MCHP_PIT64B_MR_ONE_SHOT define
>> - move the new lines introduced in Makefile and Kconfig at the end of files
>> - collect Rob's Reviewed-by tag on patch 1/2
>> - review the commit message of patch 2/2
>>
>> Changes in v2:
>> - remove clock-frequency DT binding and hardcoded it in the driver
>> - initialize best_pres variable in mchp_pit64b_pres_prepare()
>> - remove MCHP_PIT64B_DEF_FREQ
>> - get rid of patches 3-5 from v1 [1] since there is no entry in MAINTAINERS file
>>   for this entry. It was removed in
>>   commit 44015a8181a5 ("MAINTAINERS: at91: remove the TC entry")
>>
>> [1] https://lore.kernel.org/lkml/1552580772-8499-1-git-send-email-claudiu.beznea@microchip.com/
>>
>>  drivers/clocksource/Kconfig                  |   6 +
>>  drivers/clocksource/Makefile                 |   1 +
>>  drivers/clocksource/timer-microchip-pit64b.c | 501 +++++++++++++++++++++++++++
>>  3 files changed, 508 insertions(+)
>>  create mode 100644 drivers/clocksource/timer-microchip-pit64b.c
>>
>> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
>> index 5fdd76cb1768..eaadbc42ce4a 100644
>> --- a/drivers/clocksource/Kconfig
>> +++ b/drivers/clocksource/Kconfig
>> @@ -697,4 +697,10 @@ config INGENIC_TIMER
>>       help
>>         Support for the timer/counter unit of the Ingenic JZ SoCs.
>>
>> +config MICROCHIP_PIT64B
>> +     bool "Microchip PIT64B support"
>> +     depends on OF || COMPILE_TEST
>> +     help
>> +       This option enables Microchip PIT64B timer.
>> +
>>  endmenu
>> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
>> index 4dfe4225ece7..713686faa549 100644
>> --- a/drivers/clocksource/Makefile
>> +++ b/drivers/clocksource/Makefile
>> @@ -88,3 +88,4 @@ obj-$(CONFIG_RISCV_TIMER)           += timer-riscv.o
>>  obj-$(CONFIG_CSKY_MP_TIMER)          += timer-mp-csky.o
>>  obj-$(CONFIG_GX6605S_TIMER)          += timer-gx6605s.o
>>  obj-$(CONFIG_HYPERV_TIMER)           += hyperv_timer.o
>> +obj-$(CONFIG_MICROCHIP_PIT64B)               += timer-microchip-pit64b.o
>> diff --git a/drivers/clocksource/timer-microchip-pit64b.c b/drivers/clocksource/timer-microchip-pit64b.c
>> new file mode 100644
>> index 000000000000..293e1ab39729
>> --- /dev/null
>> +++ b/drivers/clocksource/timer-microchip-pit64b.c
>> @@ -0,0 +1,501 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * 64-bit Periodic Interval Timer driver
>> + *
>> + * Copyright (C) 2019 Microchip Technology Inc. and its subsidiaries
>> + *
>> + * Author: Claudiu Beznea <claudiu.beznea@microchip.com>
>> + */
>> +
>> +#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_ONE_SHOT              (0)
>> +#define MCHP_PIT64B_MR_SGCLK         BIT(3)
>> +#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_LSBMASK          GENMASK_ULL(31, 0)
>> +#define MCHP_PIT64B_PRESCALER(p)     (MCHP_PIT64B_MR_PRES & ((p) << 8))
>> +#define MCHP_PIT64B_DEF_CS_FREQ              5000000UL       /* 5 MHz */
>> +#define MCHP_PIT64B_DEF_CE_FREQ              32768           /* 32 KHz */
>> +
>> +#define MCHP_PIT64B_NAME             "pit64b"
>> +
>> +/**
>> + * struct mchp_pit64b_timer - PIT64B timer data structure
>> + * @base: base address of PIT64B hardware block
>> + * @pclk: PIT64B's peripheral clock
>> + * @gclk: PIT64B's generic clock
>> + * @cycles: timer's number of cycles
>> + * @irq: PIT64B's Linux IRQ number
>> + * @pres: prescaler value for the chosen clock
>> + */
>> +struct mchp_pit64b_timer {
>> +     void __iomem    *base;
>> +     struct clk      *pclk;
>> +     struct clk      *gclk;
>> +     u64             cycles;
>> +     u32             irq;
> 
> irq is not needed, a local variable is enough to setup the timer.

I kept it here to be able to use the same function (mchp_pit64b_reset())
for configuring both the timer that needs to be used for clocksource
feeding and the timer that needs to be used for clockevent feeding.


> 
> 
>> +     u8              pres;
>> +};
> 
> The field pres and cycles are needed to reset the clockevent, is it
> really mandatory to set them again and again from the value stored?

pres is chosen based on the clocks that are feeding the timer, and this is
done once, at probe. This IP is fed by 2 clocks, one fixed from PMC one
configurable via PMC. Only one of these 2 can feed the counter. In the IP
there is also a prescaler that divides the chosen clock. The counter in
this IP is incremented at the frequency of chosen clock (pclk or gclk)
divided by chosen prescaler. The configuration for prescaler is cleared
every time IP is reseted. This is the reason I kept it in this structure: I
need it to reconfigure properly the timer's frequency in:
mchp_pit64b_clkevt_set_periodic()
mchp_pit64b_clkevt_set_oneshot()
mchp_pit64b_clkevt_set_next_event()
mchp_pit64b_clkevt_resume()
mchp_pit64b_dt_init_clksrc()

With regards to cycles, I kept it here for mchp_pit64b_clkevt_set_periodic()
mchp_pit64b_clkevt_set_oneshot()
mchp_pit64b_clkevt_resume()
so that after this function to have configured the timer with cycles
computed on probe, based on clock frequency and not to recompute it in the
functions specified above.

> 
>> +
>> +/**
>> + * mchp_pit64b_clksrc - PIT64B clocksource data structure
>> + * @timer: PIT64B timer
>> + * @clksrc: clocksource
>> + */
>> +struct mchp_pit64b_clksrc {
>> +     struct mchp_pit64b_timer        timer;
>> +     struct clocksource              clksrc;
>> +};
> 
> clksrc would be not needed here if you use the function:
>         clocksource_mmio_init()

OK, I'll switch to clocksource_mmio_init().

> 
>> +#define clksrc_to_mchp_pit64b_timer(x) \
>> +     (&(container_of(x, struct mchp_pit64b_clksrc, clksrc))->timer)
> 
> No dereference should happen here. We should end up with a single structure:

OK!

> 
> struct mchp_pit64b_timer {
>         void *__iomem                   *base;
>         struct clk                      *pclk;
>         struct clk                      *gclk;
>         struct clock_event_device       clkevt
> };

OK, I'll analyze this, probably, using clocksource_mmio_init() may help
with having this single structure.

> 
>> + * mchp_pit64b_clkevt - PIT64B clockevent data structure
>> + * @timer: PIT64B timer
>> + * @clkevt: clockevent
>> + */
>> +struct mchp_pit64b_clkevt {
>> +     struct mchp_pit64b_timer        timer;
>> +     struct clock_event_device       clkevt;
>> +};
>> +
>> +#define clkevt_to_mchp_pit64b_timer(x) \
>> +     (&(container_of(x, struct mchp_pit64b_clkevt, clkevt))->timer)
> 
> Same comment.
> 
>> +> +static void __iomem *mchp_pit64b_cs_base;
>>
>> +static inline u64 mchp_pit64b_get_period(void __iomem *base)
> 
> The 'get_period' name is confusing. Can you replace that by 'get_counter'?

Sure!

> 
> Also, the 'high' part change may be checked, like:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/tree/drivers/clocksource/timer-imx-sysctr.c?h=bleeding-edge#n51

The IP guarantees that the reading of counter is atomic if
MCHP_PIT64B_TLSBR is read first. With this, would you still want to add the
check you mention above?

> 
> You should consider if using only the first 32bits wouldn't be enough
> (max duration before wrapping up). Using the 64bits here has a
> significant impact on the performances. Up to you to decide.

OK! Thank you!

> 
>> +{
>> +     unsigned long   flags;
>> +     u32             low, high;
>> +
>> +     raw_local_irq_save(flags);
>> +     /*
>> +      * When using a 64 bit period TLSB must be read first, followed by the
>> +      * read of TMSB. This sequence generates an atomic read of the 64 bit
>> +      * timer value whatever the lapse of time between the accesses.
>> +      */
>> +     low = readl_relaxed(base + MCHP_PIT64B_TLSBR);
>> +     high = readl_relaxed(base + MCHP_PIT64B_TMSBR);
> 
> Add line for clarity.

OK!

> 
>> +     raw_local_irq_restore(flags);
>> +
>> +     return (((u64)high << 32) | low);
>> +}
>> +
>> +static inline void mchp_pit64b_reset(struct mchp_pit64b_timer *timer,
>> +                                  u64 cycles, u32 mode)
>> +{
>> +     u32 low, high;
>> +
>> +     low = cycles & MCHP_PIT64B_LSBMASK;
>> +     high = cycles >> 32;
>> +
>> +     mode |= MCHP_PIT64B_PRESCALER(timer->pres);
>> +     if (timer->gclk)
>> +             mode |= MCHP_PIT64B_MR_SGCLK;
> 
> Why not pre-compute 'mode', make it a field of the timer struct and
> change the value at init time and in set_periodic and set_oneshot?

To avoid adding another member to struct mchp_pit64b_timer thinking that
having pres and gclk may be enough to detect how timer's mode could be
setup. I'll double check it and try to do it better.

> 
>> +     writel_relaxed(MCHP_PIT64B_CR_SWRST, timer->base + MCHP_PIT64B_CR);
>> +     writel_relaxed(mode, timer->base + MCHP_PIT64B_MR);
>> +     writel_relaxed(high, timer->base + MCHP_PIT64B_MSB_PR);
>> +     writel_relaxed(low, timer->base + MCHP_PIT64B_LSB_PR);
>> +     if (timer->irq) {
> 
> Clocksource reset is only needed at init time, it can be done separetely
> and this function will be called for the clockevent only, hence the
> check won't be necessary.

I kept it here to use the same function to reset clocksource's and
clockevent's timer.

> 
>> +             writel_relaxed(MCHP_PIT64B_IER_PERIOD,
>> +                            timer->base + MCHP_PIT64B_IER);
>> +     }
>> +     writel_relaxed(MCHP_PIT64B_CR_START, timer->base + MCHP_PIT64B_CR);
>> +}
>> +
>> +static u64 mchp_pit64b_clksrc_read(struct clocksource *cs)
>> +{
>> +     struct mchp_pit64b_timer *timer = clksrc_to_mchp_pit64b_timer(cs);
>> +
>> +     return mchp_pit64b_get_period(timer->base);
>> +}
>> +
>> +static u64 mchp_pit64b_sched_read_clk(void)
>> +{
>> +     return mchp_pit64b_get_period(mchp_pit64b_cs_base);
>> +}
>> +
>> +static int mchp_pit64b_clkevt_shutdown(struct clock_event_device *cedev)
>> +{
>> +     struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
>> +
>> +     writel_relaxed(MCHP_PIT64B_CR_SWRST, timer->base + MCHP_PIT64B_CR);
>> +
>> +     return 0;
>> +}
>> +
>> +static int mchp_pit64b_clkevt_set_periodic(struct clock_event_device *cedev)
>> +{
>> +     struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
>> +
>> +     mchp_pit64b_reset(timer, timer->cycles, MCHP_PIT64B_MR_CONT);
>> +
>> +     return 0;
>> +}
>> +
>> +static int mchp_pit64b_clkevt_set_oneshot(struct clock_event_device *cedev)
>> +{
>> +     struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
>> +
>> +     mchp_pit64b_reset(timer, timer->cycles, MCHP_PIT64B_MR_ONE_SHOT);
>> +
>> +     return 0;
>> +}
>> +
>> +static int mchp_pit64b_clkevt_set_next_event(unsigned long evt,
>> +                                          struct clock_event_device *cedev)
>> +{
>> +     struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
>> +
>> +     mchp_pit64b_reset(timer, evt, MCHP_PIT64B_MR_ONE_SHOT);
>> +
>> +     return 0;
>> +}
>> +
>> +static void mchp_pit64b_clkevt_suspend(struct clock_event_device *cedev)
>> +{
>> +     struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
>> +
>> +     writel_relaxed(MCHP_PIT64B_CR_SWRST, timer->base + MCHP_PIT64B_CR);
>> +     if (timer->gclk)
>> +             clk_disable_unprepare(timer->gclk);
>> +     clk_disable_unprepare(timer->pclk);
>> +}
>> +
>> +static void mchp_pit64b_clkevt_resume(struct clock_event_device *cedev)
>> +{
>> +     struct mchp_pit64b_timer *timer = clkevt_to_mchp_pit64b_timer(cedev);
>> +     u32 mode = MCHP_PIT64B_MR_ONE_SHOT;
>> +
>> +     clk_prepare_enable(timer->pclk);
>> +     if (timer->gclk)
>> +             clk_prepare_enable(timer->gclk);
>> +
>> +     if (clockevent_state_periodic(cedev))
>> +             mode = MCHP_PIT64B_MR_CONT;
>> +
>> +     mchp_pit64b_reset(timer, timer->cycles, mode);
>> +}
>> +
>> +static irqreturn_t mchp_pit64b_interrupt(int irq, void *dev_id)
>> +{
>> +     struct mchp_pit64b_clkevt *irq_data = dev_id;
>> +
>> +     /* Need to clear the interrupt. */
>> +     readl_relaxed(irq_data->timer.base + MCHP_PIT64B_ISR);
>> +
>> +     irq_data->clkevt.event_handler(&irq_data->clkevt);
>> +
>> +     return IRQ_HANDLED;
>> +}
>> +
>> +static void __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;
>> +     }
>> +
>> +     /* Use the bigest prescaler if we didn't match one. */
>> +     if (*pres == MCHP_PIT64B_PRES_MAX)
>> +             *pres = MCHP_PIT64B_PRES_MAX - 1;
>> +}
>> +
>> +/**
>> + * mchp_pit64b_pres_prepare - prepare PIT64B clocks and internal prescaler
>> + *
>> + * PIT64B timer may be fed by gclk or pclk. When gclk is used its rate has to
>> + * be at least 3 times lower that pclk's rate. pclk rate is fixed, gclk rate
>> + * could be changed via clock APIs. The chosen clock (pclk or gclk) could be
>> + * divided by the internal PIT64B's divider.
>> + *
>> + * This function, first tries to use GCLK by requesting the desired rate from
>> + * PMC and then using the internal PIT64B prescaller, if any, to reach the
>> + * requested rate. If PCLK/GCLK < 3 (condition requested by PIT64B hardware)
>> + * then the function falls back on using PCLK as clock source for PIT64B timer
>> + * choosing the highest prescaler in case it doesn't locate one to match the
>> + * requested frequency.
>> + *
>> + * Below is presented the PIT64B block in relation with PMC:
>> + *
>> + *                                PIT64B
>> + *  PMC             +------------------------------------+
>> + * +----+           |   +-----+                          |
>> + * |    |-->gclk -->|-->|     |    +---------+  +-----+  |
>> + * |    |           |   | MUX |--->| Divider |->|timer|  |
>> + * |    |-->pclk -->|-->|     |    +---------+  +-----+  |
>> + * +----+           |   +-----+                          |
>> + *                  |      ^                             |
>> + *                  |     sel                            |
>> + *                  +------------------------------------+
>> + *
>> + * Where:
>> + *   - gclk rate <= pclk rate/3
>> + *   - gclk rate could be requested from PMC
>> + *   - pclk rate is fixed (cannot be requested from PMC)
>> + */
>> +static int __init mchp_pit64b_pres_prepare(struct mchp_pit64b_timer *timer,
>> +                                        unsigned long max_rate)
>> +{
>> +     unsigned long pclk_rate, diff = 0, best_diff = ULONG_MAX;
>> +     long gclk_round = 0;
>> +     u32 pres, best_pres = 0;
>> +
>> +     pclk_rate = clk_get_rate(timer->pclk);
>> +     if (!pclk_rate)
>> +             return -EINVAL;
>> +
>> +     /* Try using GCLK. */
>> +     gclk_round = clk_round_rate(timer->gclk, max_rate);
>> +     if (gclk_round < 0)
>> +             goto pclk;
>> +
>> +     if (pclk_rate / gclk_round < 3)
>> +             goto pclk;
>> +
>> +     mchp_pit64b_pres_compute(&pres, gclk_round, max_rate);
>> +     best_diff = abs(gclk_round / (pres + 1) - max_rate);
>> +     best_pres = pres;
>> +
>> +     if (!best_diff)
>> +             goto done;
>> +
>> +pclk:
>> +     /* Check if requested rate could be obtained using PCLK. */
>> +     mchp_pit64b_pres_compute(&pres, pclk_rate, max_rate);
>> +     diff = abs(pclk_rate / (pres + 1) - max_rate);
>> +
>> +     if (best_diff > diff) {
>> +             /* Use PCLK. */
>> +             timer->gclk = NULL;
>> +             best_pres = pres;
>> +     } else {
>> +             /* Use GCLK. */
>> +             clk_set_rate(timer->gclk, gclk_round);
>> +     }
>> +
>> +done:
>> +     timer->pres = best_pres;
>> +     pr_info("PIT64B: using clk=%s with prescaler %u, freq=%lu [Hz]\n",
>> +             timer->gclk ? "gclk" : "pclk", timer->pres,
>> +             timer->gclk ? gclk_round / (timer->pres + 1)
>> +                         : pclk_rate / (timer->pres + 1));
>> +
>> +     return 0;
>> +}
>> +
>> +static int __init mchp_pit64b_timer_init(struct device_node *node,
>> +                                      struct mchp_pit64b_timer *timer,
>> +                                      u32 freq, bool is_clkevt)
>> +{
>> +     int ret;
>> +
>> +     timer->pclk = of_clk_get_by_name(node, "pclk");
>> +     if (IS_ERR(timer->pclk))
>> +             return PTR_ERR(timer->pclk);
>> +
>> +     timer->gclk = of_clk_get_by_name(node, "gclk");
>> +     if (IS_ERR(timer->gclk))
>> +             return PTR_ERR(timer->gclk);
>> +
>> +     timer->base = of_iomap(node, 0);
>> +     if (!timer->base)
>> +             return -ENXIO;
>> +
>> +     if (is_clkevt) {
>> +             timer->irq = irq_of_parse_and_map(node, 0);
>> +             if (!timer->irq) {
>> +                     ret = -ENODEV;
>> +                     goto io_unmap;
>> +             }
>> +     }
>> +
>> +     ret = mchp_pit64b_pres_prepare(timer, freq);
>> +     if (ret)
>> +             goto irq_unmap;
>> +
>> +     ret = clk_prepare_enable(timer->pclk);
>> +     if (ret)
>> +             goto irq_unmap;
>> +
>> +     if (timer->gclk) {
>> +             ret = clk_prepare_enable(timer->gclk);
>> +             if (ret)
>> +                     goto pclk_unprepare;
>> +     }
>> +
>> +     return 0;
>> +
>> +pclk_unprepare:
>> +     clk_disable_unprepare(timer->pclk);
>> +irq_unmap:
>> +     irq_dispose_mapping(timer->irq);
>> +io_unmap:
>> +     iounmap(timer->base);
>> +
>> +     return ret;
>> +}
>> +
>> +static void __init mchp_pit64b_timer_cleanup(struct mchp_pit64b_timer *timer)
>> +{
>> +     if (timer->gclk)
>> +             clk_disable_unprepare(timer->gclk);
>> +     clk_disable_unprepare(timer->pclk);
>> +     irq_dispose_mapping(timer->irq);
>> +     iounmap(timer->base);
>> +}
>> +
>> +static int __init mchp_pit64b_dt_init_clksrc(struct device_node *node)
>> +{
>> +     struct mchp_pit64b_clksrc *cs;
>> +     unsigned long clk_rate;
>> +     int ret;
>> +
>> +     cs = kzalloc(sizeof(*cs), GFP_KERNEL);
>> +     if (!cs)
>> +             return -ENOMEM;
>> +
>> +     ret = mchp_pit64b_timer_init(node, &cs->timer, MCHP_PIT64B_DEF_CS_FREQ,
>> +                                  false);
>> +     if (ret)
>> +             goto free;
>> +
>> +     if (cs->timer.gclk)
>> +             clk_rate = clk_get_rate(cs->timer.gclk);
>> +     else
>> +             clk_rate = clk_get_rate(cs->timer.pclk);
>> +
>> +     clk_rate = clk_rate / (cs->timer.pres + 1);
>> +     cs->timer.cycles = ULLONG_MAX;
>> +     mchp_pit64b_reset(&cs->timer, cs->timer.cycles, MCHP_PIT64B_MR_CONT);
>> +
>> +     cs->clksrc.name = MCHP_PIT64B_NAME;
>> +     cs->clksrc.mask = CLOCKSOURCE_MASK(64);
>> +     cs->clksrc.flags = CLOCK_SOURCE_IS_CONTINUOUS;
>> +     cs->clksrc.rating = 210;
>> +     cs->clksrc.read = mchp_pit64b_clksrc_read;
>> +
>> +     ret = clocksource_register_hz(&cs->clksrc, clk_rate);
>> +     if (ret) {
>> +             pr_debug("clksrc: Failed to register PIT64B clocksource!\n");
>> +             goto timer_cleanup;
>> +     }
>> +
>> +     mchp_pit64b_cs_base = cs->timer.base;
>> +     sched_clock_register(mchp_pit64b_sched_read_clk, 64, clk_rate);
>> +
>> +     return 0;
>> +
>> +timer_cleanup:
>> +     mchp_pit64b_timer_cleanup(&cs->timer);
>> +free:
>> +     kfree(cs);
>> +     return ret;
>> +}
>> +
>> +static int __init mchp_pit64b_dt_init_clkevt(struct device_node *node)
>> +{
>> +     struct mchp_pit64b_clkevt *ce;
>> +     unsigned long clk_rate;
>> +     int ret;
>> +
>> +     ce = kzalloc(sizeof(*ce), GFP_KERNEL);
>> +     if (!ce)
>> +             return -ENOMEM;
>> +
>> +     ret = mchp_pit64b_timer_init(node, &ce->timer, MCHP_PIT64B_DEF_CE_FREQ,
>> +                                  true);
>> +     if (ret)
>> +             goto free;
>> +
>> +     if (ce->timer.gclk)
>> +             clk_rate = clk_get_rate(ce->timer.gclk);
>> +     else
>> +             clk_rate = clk_get_rate(ce->timer.pclk);
>> +
>> +     clk_rate = clk_rate / (ce->timer.pres + 1);
>> +     ce->timer.cycles = DIV_ROUND_CLOSEST(clk_rate, HZ);
>> +
>> +     ce->clkevt.name = MCHP_PIT64B_NAME;
>> +     ce->clkevt.features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_PERIODIC;
>> +     ce->clkevt.rating = 150;
>> +     ce->clkevt.set_state_shutdown = mchp_pit64b_clkevt_shutdown;
>> +     ce->clkevt.set_state_periodic = mchp_pit64b_clkevt_set_periodic;
>> +     ce->clkevt.set_state_oneshot = mchp_pit64b_clkevt_set_oneshot;
>> +     ce->clkevt.set_next_event = mchp_pit64b_clkevt_set_next_event;
>> +     ce->clkevt.suspend = mchp_pit64b_clkevt_suspend;
>> +     ce->clkevt.resume = mchp_pit64b_clkevt_resume;
>> +     ce->clkevt.cpumask = cpumask_of(0);
>> +     ce->clkevt.irq = ce->timer.irq;
>> +
>> +     ret = request_irq(ce->timer.irq, mchp_pit64b_interrupt, IRQF_TIMER,
>> +                       "pit64b_tick", ce);
>> +     if (ret) {
>> +             pr_debug("clkevt: Failed to setup PIT64B IRQ\n");
>> +             goto timer_cleanup;
>> +     }
>> +
>> +     clockevents_config_and_register(&ce->clkevt, clk_rate, 1, ULONG_MAX);
>> +
>> +     return 0;
>> +
>> +timer_cleanup:
>> +     mchp_pit64b_timer_cleanup(&ce->timer);
>> +free:
>> +     kfree(ce);
>> +     return ret;
>> +}
>> +
>> +static int __init mchp_pit64b_dt_init(struct device_node *node)
>> +{
>> +     static int inits;
>> +
>> +     switch (inits++) {
>> +     case 0:
>> +             /* 1st request, register clockevent. */
>> +             return mchp_pit64b_dt_init_clkevt(node);
>> +     case 1:
>> +             /* 2nd request, register clocksource. */
>> +             return mchp_pit64b_dt_init_clksrc(node);
>> +     }
>> +
>> +     /* The rest, don't care. */
>> +     return -EINVAL;
>> +}
>> +
>> +TIMER_OF_DECLARE(mchp_pit64b, "microchip,sam9x60-pit64b", mchp_pit64b_dt_init);
>>
> 
> 
> --
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> 
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> 

Re: [PATCH v3 2/2] clocksource/drivers/timer-microchip-pit64b: add Microchip PIT64B support

[Daniel Lezcano]

On 10/12/2019 12:43, Claudiu.Beznea@microchip.com wrote:
> 
> 
> On 09.12.2019 19:04, Daniel Lezcano wrote:
>> On 04/12/2019 15:42, Claudiu Beznea wrote:
>>> 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.
>>> The driver uses PIT64B timer for clocksource or clockevent. First
>>> requested timer would be registered as clockevent, second one would be
>>> registered as clocksource. 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 <claudiu.beznea@microchip.com>
>>> ---

[ ... ]

>> Also, the 'high' part change may be checked, like:
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/tree/drivers/clocksource/timer-imx-sysctr.c?h=bleeding-edge#n51
> 
> The IP guarantees that the reading of counter is atomic if
> MCHP_PIT64B_TLSBR is read first. With this, would you still want to add the
> check you mention above?

No, sorry I should have read the comment :/

[ ... ]


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