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

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Message-ID: <CAFiDJ5_zsyQ92W4iYG2Ria12TKpkFa8Au5noos1=gtq6_aPyjg@mail.gmail.com>
Date:	Tue, 28 Oct 2014 10:46:29 +0800
From:	Ley Foon Tan <lftan@...era.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Linux-Arch <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Chung-Lin Tang <cltang@...esourcery.com>
Subject: Re: [PATCH v5 21/29] nios2: Time keeping

On Sun, Oct 26, 2014 at 5:10 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> 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?
This is suggestion from Arnd to use read_current_timer instead of using
expensive delay loop calibration during boot.
>
>> +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.
Noted.
>
>> +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.
Noted.
>
>> +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?
Yes, we can make this statically allocated and initialized.

>
>> +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.
Same for this.
>
>> +/*
>> + * 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.
Okay, will move into nios2_time_init().

Thanks.

Regards
Ley Foon
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