Re: [PATCH 04/17] clocksource: Add PLX Technology RPS Timer

From: Daniel Lezcano
Date: Thu Mar 17 2016 - 12:13:55 EST

Hi Neil,

On 03/03/2016 12:39 PM, Neil Armstrong wrote:
Add clocksource and clockevent driver from dual RPS timer.

please elaborate the log: describe the timer, how it works, is there a pointer to doc, freq, etc ...

CC: Ma Haijun <mahaijuns@xxxxxxxxx>
Signed-off-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
---
drivers/clocksource/Kconfig | 6 +
drivers/clocksource/Makefile | 1 +
drivers/clocksource/timer-rps.c | 249 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 256 insertions(+)
create mode 100644 drivers/clocksource/timer-rps.c

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 33db740..f79bc0f 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -276,6 +276,12 @@ config VF_PIT_TIMER
help
Support for Period Interrupt Timer on Freescale Vybrid Family SoCs.

+config CLKSRC_RPS_TIMER
+ bool
+ select CLKSRC_MMIO
+ help
+ This enables support for the PLX Tech OXNAS RPS timers.
+

Please check DIGICOLOR_TIMER or DW_APB_TIMER or ROCKCHIP_TIMER or ARMADA_370_XP_TIMER or ... config section and try to stick to the same pattern.

config SYS_SUPPORTS_SH_CMT
bool

diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index dc2b899..120bc09 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -46,6 +46,7 @@ obj-$(CONFIG_CLKSRC_QCOM) += qcom-timer.o
obj-$(CONFIG_MTK_TIMER) += mtk_timer.o
obj-$(CONFIG_CLKSRC_PISTACHIO) += time-pistachio.o
obj-$(CONFIG_CLKSRC_TI_32K) += timer-ti-32k.o
+obj-$(CONFIG_CLKSRC_RPS_TIMER) += timer-rps.o

obj-$(CONFIG_ARM_ARCH_TIMER) += arm_arch_timer.o
obj-$(CONFIG_ARM_GLOBAL_TIMER) += arm_global_timer.o
diff --git a/drivers/clocksource/timer-rps.c b/drivers/clocksource/timer-rps.c
new file mode 100644
index 0000000..79621b8
--- /dev/null
+++ b/drivers/clocksource/timer-rps.c
@@ -0,0 +1,249 @@
+/*
+ * drivers/clocksource/timer-rps.c
+ *
+ * Copyright (C) 2009 Oxford Semiconductor Ltd
+ * Copyright (C) 2013 Ma Haijun <mahaijuns@xxxxxxxxx>
+ * Copyright (C) 2016 Neil Armstrong <narmstrong@xxxxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/io.h>
+#include <linux/clockchips.h>
+#include <linux/clk.h>
+#include <linux/of_irq.h>
+#include <linux/of_address.h>
+#include <linux/sched_clock.h>
+
+/* TIMER1 as tick
+ * TIMER2 as clocksource
+ */

Comment format:

/*
* TIMER1 used as tick
* TIMER2 used as clocksource
*/

+enum {
+ TIMER_LOAD = 0,
+ TIMER_CURR = 4,
+ TIMER_CTRL = 8,
+ TIMER_CLRINT = 0xC,
+
+ TIMER_BITS = 24,
+
+ TIMER_MAX_VAL = (1 << TIMER_BITS) - 1,
+
+ TIMER_PERIODIC = (1 << 6),
+ TIMER_ENABLE = (1 << 7),
+
+ TIMER_DIV1 = (0 << 2),
+ TIMER_DIV16 = (1 << 2),
+ TIMER_DIV256 = (2 << 2),
+
+ TIMER1_OFFSET = 0,
+ TIMER2_OFFSET = 0x20,
+};

What is the point of having this unorganized enum with duplicate values ? and why TIMER_DIV1 = (0 << 2) ?

Replace by #define.

+/* Clockevent */
+
+static unsigned long timer_period = HZ;
+static unsigned timer_prescaler = 1;
+static void __iomem *timer_base;

Encapsulate these variables into a structure and use container_of.

+
+static irqreturn_t rps_timer_irq(int irq, void *dev_id)
+{
+ struct clock_event_device *evt = dev_id;
+
+ iowrite32(0, timer_base + TIMER_CLRINT);
+
+ evt->event_handler(evt);
+
+ return IRQ_HANDLED;
+}
+
+static void rps_timer_config(unsigned long period, unsigned periodic)
+{
+ uint32_t cfg = 0;
+
+ if (period)
+ cfg |= TIMER_ENABLE;
+
+ if (periodic)
+ cfg |= TIMER_PERIODIC;
+
+ switch (timer_prescaler) {
+ case 1:
+ cfg |= TIMER_DIV1;
+ break;
+ case 16:
+ cfg |= TIMER_DIV16;
+ break;
+ case 256:
+ cfg |= TIMER_DIV256;
+ break;
+ }

No direct value (1, 16, 256) but macros please.

+ iowrite32(period, timer_base + TIMER_LOAD);
+ iowrite32(cfg, timer_base + TIMER_CTRL);
+}
+
+static int rps_timer_shutdown(struct clock_event_device *evt)
+{
+ if (!clockevent_state_periodic(evt))
+ return 0;
+
+ rps_timer_config(0, 0);
+
+ return 0;
+}
+
+static int rps_timer_set_periodic(struct clock_event_device *evt)
+{
+ rps_timer_config(timer_period, 1);
+
+ return 0;
+}
+
+static int rps_timer_set_oneshot(struct clock_event_device *evt)
+{
+ rps_timer_config(timer_period, 0);
+
+ return 0;
+}
+
+static int rps_timer_next_event(unsigned long delta,
+ struct clock_event_device *evt)
+{
+ rps_timer_config(delta, 0);
+
+ return 0;
+}
+
+static struct clock_event_device rps_clockevent = {
+ .name = "rps",
+ .features = CLOCK_EVT_FEAT_PERIODIC |
+ CLOCK_EVT_FEAT_ONESHOT,
+ .tick_resume = rps_timer_shutdown,
+ .set_state_shutdown = rps_timer_shutdown,
+ .set_state_periodic = rps_timer_set_periodic,
+ .set_state_oneshot = rps_timer_set_oneshot,
+ .set_next_event = rps_timer_next_event,
+ .rating = 200,
+};
+
+static void __init rps_clockevent_init(void __iomem *base, ulong ref_rate,
+ int irq)
+{
+ timer_base = base;
+
+ /* Start with prescaler 1 */
+ timer_prescaler = 1;
+ timer_period = DIV_ROUND_UP(ref_rate, HZ);
+
+ if (timer_period > TIMER_MAX_VAL) {
+ timer_prescaler = 16;
+ timer_period = DIV_ROUND_UP(ref_rate / timer_prescaler, HZ);

Using macro and bit shifting will be nicer.

+ }
+ if (timer_period > TIMER_MAX_VAL) {
+ timer_prescaler = 256;
+ timer_period = DIV_ROUND_UP(ref_rate / timer_prescaler, HZ);
+ }
+ rps_clockevent.cpumask = cpu_possible_mask;
+ rps_clockevent.irq = irq;

So if you are using such cpumask, I suggest you have a look at the DYNIRQ flag.

+ clockevents_config_and_register(&rps_clockevent,
+ ref_rate / timer_prescaler,
+ 1,
+ TIMER_MAX_VAL);
+
+ pr_info("rps: Registered clock event rate %luHz prescaler %d period %lu\n",
+ ref_rate,
+ timer_prescaler,
+ timer_period);
+}
+
+/* Clocksource */
+
+static void __iomem *timer_curr;
+
+static u64 notrace rps_read_sched_clock(void)
+{
+ return ~readl_relaxed(timer_curr);
+}
+
+static void __init rps_clocksource_init(void __iomem *base, ulong ref_rate)
+{
+ int ret;
+ ulong clock_rate;
+ /* use prescale 16 */
+ clock_rate = ref_rate / 16;
+
+ iowrite32(TIMER_MAX_VAL, base + TIMER_LOAD);
+ iowrite32(TIMER_PERIODIC | TIMER_ENABLE | TIMER_DIV16,
+ base + TIMER_CTRL);
+
+ timer_curr = base + TIMER_CURR;
+ sched_clock_register(rps_read_sched_clock, TIMER_BITS, clock_rate);
+ ret = clocksource_mmio_init(base + TIMER_CURR, "rps_clocksource_timer",
+ clock_rate, 250, TIMER_BITS,
+ clocksource_mmio_readl_down);
+ if (ret)
+ panic("can't register clocksource\n");

No panic, just an error.

+ pr_info("rps: Registered clocksource rate %luHz\n", clock_rate);
+}
+
+static struct irqaction rps_timer_irqaction = {
+ .name = "rps_timer",
+ .flags = IRQF_TIMER | IRQF_IRQPOLL,
+ .handler = rps_timer_irq,
+ .dev_id = &rps_clockevent,
+};
+
+static void __init rps_timer_init(struct device_node *np)
+{
+ struct clk *refclk;
+ unsigned long ref_rate;
+ void __iomem *base;
+ int irq, ret;
+
+ refclk = of_clk_get(np, 0);
+
+ if (IS_ERR(refclk) || clk_prepare_enable(refclk))
+ panic("rps_timer_init: failed to get refclk\n");

no panic.

+ ref_rate = clk_get_rate(refclk);
+
+ base = of_iomap(np, 0);
+ if (!base)
+ panic("rps_timer_init: failed to map io\n");
+
+ irq = irq_of_parse_and_map(np, 0);
+ if (irq < 0)
+ panic("rps_timer_init: failed to parse IRQ\n");

if (!irq)
no panic.

+
+ /* Disable timers */
+ iowrite32(0, base + TIMER1_OFFSET + TIMER_CTRL);
+ iowrite32(0, base + TIMER2_OFFSET + TIMER_CTRL);
+ iowrite32(0, base + TIMER1_OFFSET + TIMER_LOAD);
+ iowrite32(0, base + TIMER2_OFFSET + TIMER_LOAD);
+ iowrite32(0, base + TIMER1_OFFSET + TIMER_CLRINT);
+ iowrite32(0, base + TIMER2_OFFSET + TIMER_CLRINT);
+
+ rps_clocksource_init(base + TIMER2_OFFSET, ref_rate);
+ rps_clockevent_init(base + TIMER1_OFFSET, ref_rate, irq);
+
+ ret = setup_irq(irq, &rps_timer_irqaction);

Replace setup_irq by request_irq.

+ if (ret)
+ panic("rps_timer_init: failed to request irq\n");
+}
+
+CLOCKSOURCE_OF_DECLARE(nas782x, "plxtech,nas782x-rps-timer", rps_timer_init);


Thanks !

-- Daniel


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