linux-kernel - Re: [PATCH v6 2/2] clocksource: add J-Core timer/clocksource driver

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Date:	Thu, 4 Aug 2016 14:24:51 +0600
From:	Alexnader Kuleshov <kuleshovmail@...il.com>
To:	Rich Felker <dalias@...c.org>
Cc:	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-sh@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v6 2/2] clocksource: add J-Core timer/clocksource driver

Hello Rich,

On 08-04-16, Rich Felker wrote:
> At the hardware level, the J-Core PIT is integrated with the interrupt
> controller, but it is represented as its own device and has an
> independent programming interface. It provides a 12-bit countdown
> timer, which is not presently used, and a periodic timer. The interval
> length for the latter is programmable via a 32-bit throttle register
> whose units are determined by a bus-period register. The periodic
> timer is used to implement both periodic and oneshot clock event
> modes; in oneshot mode the interrupt handler simply disables the timer
> as soon as it fires.
>
> Despite its device tree node representing an interrupt for the PIT,
> the actual irq generated is programmable, not hard-wired. The driver
> is responsible for programming the PIT to generate the hardware irq
> number that the DT assigns to it.
>
> On SMP configurations, J-Core provides cpu-local instances of the PIT;
> no broadcast timer is needed. This driver supports the creation of the
> necessary per-cpu clock_event_device instances. The code has been
> tested and works on SMP, but will not be usable without additional
> J-Core SMP-support patches and appropriate hardware capable of running
> SMP.
>
> A nanosecond-resolution clocksource is provided using the J-Core "RTC"
> registers, which give a 64-bit seconds count and 32-bit nanoseconds.
> The driver converts these to a 64-bit nanoseconds count.
>
> Signed-off-by: Rich Felker <dalias@...c.org>
> ...
> ...
> ...
> +
> +static int jcore_pit_set_state_shutdown(struct clock_event_device *ced)
> +{
> +	struct jcore_pit *pit = container_of(ced, struct jcore_pit, ced);
> +
> +	return jcore_pit_disable(pit);
> +}
> +
> +static int jcore_pit_set_state_oneshot(struct clock_event_device *ced)
> +{
> +	struct jcore_pit *pit = container_of(ced, struct jcore_pit, ced);
> +
> +	return jcore_pit_disable(pit);
> +}

Maybe to use only jcore_pit_set_state_shutdown() for both shutdown/oneshot
states as it is implemented for some of others clocksource drivers?

all the more so as described in your commit message, they do the same:

> in oneshot mode the interrupt handler simply disables the timer
> as soon as it fires

right?

> +static int __init jcore_pit_init(struct device_node *node)
> +{
> +	int err;
> +	unsigned pit_irq, cpu;
> +	unsigned long hwirq;
> +	u32 irqprio, enable_val;
> +
> +	jcore_pit_base = of_iomap(node, 0);
> +	if (!jcore_pit_base) {
> +		pr_err("Error: Cannot map base address for J-Core PIT\n");
> +		return -ENXIO;
> +	}
> +
> +	pit_irq = irq_of_parse_and_map(node, 0);
> +	if (!pit_irq) {
> +		pr_err("Error: J-Core PIT has no IRQ\n");
> +		return -ENXIO;
> +	}
> +
> +	pr_info("Initializing J-Core PIT at %p IRQ %d\n",
> +		jcore_pit_base, pit_irq);
> +
> +	jcore_cs.name = "jcore_pit_cs";
> +	jcore_cs.rating = 400;
> +	jcore_cs.read = jcore_clocksource_read;
> +	jcore_cs.mult = 1;
> +	jcore_cs.shift = 0;
> +	jcore_cs.mask = CLOCKSOURCE_MASK(32);
> +	jcore_cs.flags = CLOCK_SOURCE_IS_CONTINUOUS;
> +
> +	err = clocksource_register_hz(&jcore_cs, NSEC_PER_SEC);
> +	if (err) {
> +		pr_err("Error registering clocksource device: %d\n", err);
> +		return err;
> +	}
> +
> +	sched_clock_register(jcore_sched_clock_read, 32, NSEC_PER_SEC);
> +
> +	jcore_pit_percpu = alloc_percpu(struct jcore_pit);
> +	if (!jcore_pit_percpu) {
> +		pr_err("Failed to allocate memory for clock event device\n");
> +		return -ENOMEM;
> +	}
> +
> +	err = request_irq(pit_irq, jcore_timer_interrupt,
> +			  IRQF_TIMER | IRQF_PERCPU,
> +			  "jcore_pit", jcore_pit_percpu);
> +	if (err) {
> +		pr_err("pit irq request failed: %d\n", err);
> +		return err;
> +	}

free_percpu() missed in a case when request_irq() failed.