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Message-ID: <B56CDBE15CE27145A4B77D2D24263E851CBE88@039-SN1MPN1-003.039d.mgd.msft.net>
Date: Wed, 22 May 2013 09:47:37 +0000
From: Lu Jingchang-B35083 <B35083@...escale.com>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"john.stultz@...aro.org" <john.stultz@...aro.org>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>
Subject: RE: [PATCH v4] clocksource: add Vybrid Family pit timer support
>-----Original Message-----
>From: Daniel Lezcano [mailto:daniel.lezcano@...aro.org]
>Sent: Tuesday, May 21, 2013 6:14 PM
>To: Lu Jingchang-B35083
>Cc: linux-kernel@...r.kernel.org; linux-arm-kernel@...ts.infradead.org;
>john.stultz@...aro.org; tglx@...utronix.de; shawn.guo@...aro.org;
>s.hauer@...gutronix.de
>Subject: Re: [PATCH v4] clocksource: add Vybrid Family pit timer support
>
>On 05/21/2013 09:27 AM, Jingchang Lu wrote:
>> Add Freescale Vybrid Family period interrupt timer support.
>>
>> Signed-off-by: Jingchang Lu <b35083@...escale.com>
>> ---
>> v4:
>> use family name names driver and symbol instead of SoC name.
>> remove redundant code.
>> use BUG_ON instead of WARN_ON.
>> add necessory comment information.
>>
>> drivers/clocksource/Kconfig | 5 +
>> drivers/clocksource/Makefile | 1 +
>> drivers/clocksource/mvf_pit_timer.c | 187
>> ++++++++++++++++++++++++++++++++++++
>> 3 files changed, 193 insertions(+)
>> create mode 100644 drivers/clocksource/mvf_pit_timer.c
>
>[ ... ]
>
>> +
>> +static int pit_set_next_event(unsigned long delta,
>> + struct clock_event_device *unused) {
>> + /*
>> + * set a new value to PITLDVAL register will not restart the timer,
>> + * to abort the current cycle and start a timer period with the new
>> + * value, the timer must be disabled and enabled again.
>> + * and the PITLAVAL should be set to delta minus one.
>
>Why delta "minus one" ?
[Lu Jingchang-B35083]
This is required by the PIT hardware, it is a down counter, the PITLAVAL register should be set to (delta-1), it will raise an interrupt when it counts down to 0. Thanks!
>
>> + */
>> + pit_timer_disable();
>> + __raw_writel(delta - 1, clkevt_base + PITLDVAL);
>> + pit_timer_enable();
>> +
>> + return 0;
>> +}
>> +
>> +static void pit_set_mode(enum clock_event_mode mode,
>> + struct clock_event_device *evt)
>> +{
>> + switch (mode) {
>> + case CLOCK_EVT_MODE_PERIODIC:
>> + pit_timer_disable();
>> + __raw_writel(cycle_per_jiffy - 1, clkevt_base + PITLDVAL);
>> + pit_timer_enable();
>
>You can call pit_set_next_event(cycle_per_jiffy, evt) instead of adding
>redundant code, no ?
[Lu Jingchang-B35083]
Yes, I will do that. Thanks!
>
>> + break;
>> + default:
>> + break;
>> + }
>> +}
>
>[ ... ]
>
>> +
>> +static struct clock_event_device clockevent_pit = {
>> + .name = "MVF pit timer",
>> + .features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
>> + .set_mode = pit_set_mode,
>> + .set_next_event = pit_set_next_event,
>> + .rating = 300,
>> +};
>> +
>> +static struct irqaction pit_timer_irq = {
>> + .name = "MVF pit timer",
>> + .flags = IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
>
>Did you take into account Thomas's comment ?
[Lu Jingchang-B35083]
Sorry, I misunderstand Thomas's meaning, I will remove IRQF_DISABLED flag. Thanks!
>
>> + .handler = pit_timer_interrupt,
>> + .dev_id = &clockevent_pit,
>> +};
>> +
>> +static int __init pit_clockevent_init(struct clk *pit_clk, int irq) {
>> + unsigned int c = clk_get_rate(pit_clk);
>> +
>> + __raw_writel(0, clkevt_base + PITTCTRL);
>> + __raw_writel(PITTFLG_TIF, clkevt_base + PITTFLG);
>> +
>> + clockevent_pit.cpumask = cpumask_of(0);
>
>The irq initialization is missing.
>
> clockevent_pit.irq = irq;
>
[Lu Jingchang-B35083]
Yes, I will add this. Thanks!
>> + clockevents_config_and_register(&clockevent_pit, c, 2, 0xffffffff);
>
>Is it possible to have a comment with the justification for these values ?
[Lu Jingchang-B35083]
Yes, I will add a comment for these values. Thanks!
>
>> +
>> + BUG_ON(setup_irq(irq, &pit_timer_irq));
>> + return 0;
>
>Everything is ok if you can't setup your timer ?
>
>> +}
>> +
>> +static void __init pit_timer_init(struct device_node *np) {
>> + struct clk *pit_clk;
>> + void __iomem *timer_base;
>> + int irq;
>> +
>> + timer_base = of_iomap(np, 0);
>> + BUG_ON(!timer_base);
>
>You raise a bug and then you go ahead setting up the address with an
>invalid value, leading to a random crash.
[Lu Jingchang-B35083]
The BUG_ON() will call BUG() if condition is true. It will print the stack trace and the current process will die, it won't go ahead, won't it? Thanks!
>
>> + /*
>> + * PIT0 and PIT1 can be chained to build a 64-bit timer,
>> + * so choose PIT2 as clocksource, PIT3 as clockevent device,
>> + * and leave PIT0 and PIT1 unused for anyone else who needs them.
>> + */
>> + clksrc_base = timer_base + PITn_OFFSET(2);
>> + clkevt_base = timer_base + PITn_OFFSET(3);
>> +
>> + irq = irq_of_parse_and_map(np, 0);
>> +
>> + pit_clk = of_clk_get(np, 0);
>> + BUG_ON(IS_ERR(pit_clk));
>> +
>> + BUG_ON(clk_prepare_enable(pit_clk));
>
>Same here.
>
>> + cycle_per_jiffy = clk_get_rate(pit_clk)/(HZ);
>> +
>> + /* enable the pit module */
>> + __raw_writel(~PITMCR_MDIS, timer_base + PITMCR);
>> +
>> + BUG_ON(pit_clocksource_init(pit_clk));
>> +
>> + pit_clockevent_init(pit_clk, irq);
>
>Please, remove these BUG_ON, this is inconsistent especially with a one
>call init function. If pit_timer_init can't be initialized, just pr_err
>+ BUG.
[Lu Jingchang-B35083]
Do you mean that I should not use the BUG_ON or I need print an error information by pr_err before BUG. Thanks!
>
>Thanks
> -- Daniel
>
>
>--
> <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
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