linux-kernel - Re: [PATCH v3 04/25] clocksource: Add Owl timer

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Date:   Tue, 28 Feb 2017 18:39:50 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Andreas Färber <afaerber@...e.de>
Cc:     arm@...nel.org, linux-arm-kernel@...ts.infradead.org,
        mp-cs@...ions-semi.com, 96boards@...obotics.com,
        support@...aker.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 04/25] clocksource: Add Owl timer

On Tue, Feb 28, 2017 at 06:08:06PM +0100, Andreas Färber wrote:

[ ... ]

> > Instead of computing again and again the base, why not just precompute:
> > 
> > 	owl_clksrc_base = owl_timer_base + owl_timer_info->timer_offset[OWL_TIMER0]
> > 	owl_clkevt_base = owl_timer_base + owl_timer_info->timer_offset[OWL_TIMER1]
> > 
> >   at init time.
> > 
> > And use these variables directly in the functions.
> 
> Either that, or revert to previous simpler behavior...

Not sure to get what the 'previous simpler behavior' is, but until it does not
recompute the offset each time, I'm fine with that.

> >> +}
> >> +
> >> +static inline void owl_timer_reset(unsigned index)
> >> +{
> >> +	void __iomem *base;
> >> +
> >> +	base = owl_timer_get_base(index);
> >> +	if (!base)
> >> +		return;
> > 
> > Same here, this test is pointless.
> 
> Seems like you didn't look at the following patch yet. It sets two S500
> offsets as -1, i.e. non-existant, which then results in NULL here.

May be I missed something, but so far, the base addresses must be setup before
reset is called, no?

> >> +	writel(0, base + OWL_Tx_CTL);
> >> +	writel(0, base + OWL_Tx_VAL);
> >> +	writel(0, base + OWL_Tx_CMP);
> >> +}
> > 
> > I suggest:
> > 
> > static inline void owl_timer_reset(void __iomem *addr)
> > {
> > 	writel(0, addr + OWL_Tx_CTL);
> > 	writel(0, addr + OWL_Tx_VAL);
> > 	writel(0, addr + OWL_Tx_CMP);
> > }
> 
> OK
> 
> >> +
> >> +static u64 notrace owl_timer_sched_read(void)
> >> +{
> >> +	return (u64)readl(owl_timer_get_base(0) + OWL_Tx_VAL);
> > 
> > 	return (u64)readl(owl_clksrc_base + OWL_Tx_VAL);
> > 
> >> +}
> >> +
> > 
> > static inline int owl_timer_set_state_disable(struct clock_event_device *evt)
> > {
> > 	return writel(0, owl_clkevt_base + OWL_Tx_CTL);
> > }
> 
> That I don't like. Disabling is just setting a bit. We save a readl by
> just writing where we know it's safe. An API like this is not safe.

I don't get the point. Writing this simple function has the benefit to give the
reader the information about the disabling register. Even if it does make sense
for you, for me it has its purpose when I try to factor out different drivers
code.

> >> +static int owl_timer_set_state_shutdown(struct clock_event_device *evt)
> >> +{
> >> +	writel(0, owl_timer_get_base(0) + OWL_Tx_CTL);
> > 
> > 	return owl_timer_set_state_disable(evt);
> > 
> >> +
> >> +	return 0;
> >> +}
> >> +
> >> +static int owl_timer_set_state_oneshot(struct clock_event_device *evt)
> >> +{
> >> +	owl_timer_reset(1);
> > 
> > Do you really need to do reset here ? Why not just owl_timer_set_state_disable(evt) ?
> 
> Matches downstream, will consider changing.
> 
> >> +	return 0;
> >> +}
> >> +
> >> +static int owl_timer_tick_resume(struct clock_event_device *evt)
> >> +{
> >> +	return 0;
> >> +}
> >> +
> >> +static int owl_timer_set_next_event(unsigned long evt,
> >> +				    struct clock_event_device *ev)
> >> +{
> >> +	void __iomem *base = owl_timer_get_base(1);
> >> +
> >> +	writel(0, base + OWL_Tx_CTL);
> >> +
> >> +	writel(0, base + OWL_Tx_VAL);
> > 
> 
> Are you suggesting a while line here? The point was disable first, then
> initialize (2x), then activate. Maybe add comments instead?

I meant, base + OWL_Tx_CTL and base + OWL_Tx_VAL are set to zero since the
beginning. If their values do not change, it is not necessary to set their
values to zero again.
 
> >> +	writel(evt, base + OWL_Tx_CMP);
> >> +
> >> +	writel(OWL_Tx_CTL_EN | OWL_Tx_CTL_INTEN, base + OWL_Tx_CTL);
> >> +
> >> +	return 0;
> >> +}
> >> +
> >> +static struct clock_event_device owl_clockevent = {
> >> +	.name			= "owl_tick",
> >> +	.rating			= 200,
> >> +	.features		= CLOCK_EVT_FEAT_ONESHOT |
> >> +				  CLOCK_EVT_FEAT_DYNIRQ,
> >> +	.set_state_shutdown	= owl_timer_set_state_shutdown,
> >> +	.set_state_oneshot	= owl_timer_set_state_oneshot,
> >> +	.tick_resume		= owl_timer_tick_resume,
> >> +	.set_next_event		= owl_timer_set_next_event,
> >> +};
> >> +
> >> +static irqreturn_t owl_timer1_interrupt(int irq, void *dev_id)
> >> +{
> >> +	struct clock_event_device *evt = (struct clock_event_device *)dev_id;
> >> +
> >> +	writel(OWL_Tx_CTL_PD, owl_timer_get_base(1) + OWL_Tx_CTL);
> >> +
> >> +	evt->event_handler(evt);
> 
> Is there any guideline as to whether to clear such flag before or after?

Mmh, good question. I'm not sure it makes a different.

> >> +
> >> +	return IRQ_HANDLED;
> >> +}
> 
> Regards,
> Andreas
> 
> -- 
> SUSE Linux GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
> GF: Felix Imendörffer, Jane Smithard, Graham Norton
> HRB 21284 (AG Nürnberg)

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