linux-kernel - Re: [PATCH v5 21/29] nios2: Time keeping

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Message-ID: <alpine.DEB.2.11.1410252258570.5308@nanos>
Date:	Sat, 25 Oct 2014 23:10:34 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Ley Foon Tan <lftan@...era.com>
cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	lftan.linux@...il.com, cltang@...esourcery.com
Subject: Re: [PATCH v5 21/29] nios2: Time keeping

On Fri, 24 Oct 2014, Ley Foon Tan wrote:
> +#ifndef _ASM_NIOS2_TIMEX_H
> +#define _ASM_NIOS2_TIMEX_H
> +
> +typedef unsigned long cycles_t;
> +
> +extern cycles_t get_cycles(void);
> +
> +#define ARCH_HAS_READ_CURRENT_TIMER

Why does NIOS need that? Does it have a hardware implementation
dependent clock frequency which needs to be calibrated at boot time?

> +struct nios2_clockevent_dev {
> +	struct nios2_timer timer;
> +	struct clock_event_device ced;
> +	struct irqaction irqaction;
> +};

Why does this need its private irqaction? Timers are setup after the
interrupt subsystem, so request_irq() is good enough.

> +static void nios2_timer_config(struct nios2_timer *timer, unsigned long period,
> +	enum clock_event_mode mode)
> +{
> +	u16 ctrl;
> +
> +	/* The timer's actual period is one cycle greater than the value
> +	 * stored in the period register. */
> +	if (period)
> +		period--;

Pointless conditional. Set ce->min_delta_ticks to 1, so the core code
will never call this with period == 0 and you can unconditionally
decrement period.

> +static __init void nios2_clockevent_init(struct device_node *timer)
> +{
> +	struct nios2_clockevent_dev *ce;
> +	void __iomem *iobase;
> +	u32 freq;
> +	int irq;
> +
> +	ce = kzalloc(sizeof(*ce), GFP_KERNEL);
> +	if (!ce)
> +		panic("Failed to allocate memory for %s\n", timer->name);

What's the point of this allocation? You only install one of those, so
you can really make that whole thing statically allocated and
initialized. Or do you expect systems which use a different timer IP
for this?

> +static __init void nios2_clocksource_init(struct device_node *timer)
> +{
> +	unsigned int ctrl;
> +	void __iomem *iobase;
> +	u32 freq;
> +
> +	nios2_cs = kzalloc(sizeof(*nios2_cs), GFP_KERNEL);
> +	if (!nios2_cs)
> +		panic("Failed to allocate memory for %s\n", timer->name);

Ditto.

> +/*
> + * The first timer instance will use as a clockevent. If there are two or
> + * more instances, the second one gets used as clocksource and all
> + * others are unused.
> +*/
> +static int num_called;

This thing, horrible as it is, wants to be at least inside the
nios2_time_init() function. It has no other scope and should go away
after init along with the function itself.

> +static void __init nios2_time_init(struct device_node *timer)

Thanks,

	tglx
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