Re: [PATCH v2 04/17] clocksource: Add Owl timer

From: Daniel Lezcano
Date: Sat Feb 25 2017 - 16:59:58 EST


On Sat, Feb 25, 2017 at 12:25:32AM +0100, Andreas FÃrber wrote:
> Am 24.02.2017 um 23:29 schrieb Daniel Lezcano:
> > On Fri, Feb 24, 2017 at 04:40:42AM +0100, Andreas FÃrber wrote:
> >> Implement clocksource and clockevents for Actions Semi S500.
> >>
> >> Based on LeMaker linux-actions tree.
> >>
> >> Signed-off-by: Andreas FÃrber <afaerber@xxxxxxx>
> >
> > As this is a new driver, please give some technical information about the
> > driver itself and a pointer to documentation if it is publicly available.
>
> What technical information would that be? Which of the timers we use as
> clock source vs. clock events?

Have a look at commit 07862c1 and e4a6b37 as reference.

> The only public documentation beyond the source tree mentioned is here:
>
> http://www.lemaker.org/product-guitar-download-29.html (section 3.4)
>
> >> +#define OWL_Tx_CTL_INTEN (1 << 1)
> >> +#define OWL_Tx_CTL_EN (1 << 2)
> >
> > s/(1 << 1)/BIT(1)/
> > s/(1 << 2)/BIT(2)/
>
> OK
>

[ ... ]

> >> +static struct clock_event_device owl_clockevent = {
> >> + .name = "owl_tick",
> >> + .rating = 200,
> >> + .features = CLOCK_EVT_FEAT_ONESHOT,
> >
> > Did you consider adding CLOCK_EVT_FEAT_DYNIRQ ?
>
> No, it was not present downstream. Got a good example?

https://lwn.net/Articles/541000/

> >> + .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_timer_interrupt(int irq, void *dev_id)
> >> +{
> >> + struct clock_event_device *evt = (struct clock_event_device *)dev_id;
> >> +
> >> + evt->event_handler(evt);
> >> +
> >> + return IRQ_HANDLED;
> >> +}
> >> +
> >> +static struct irqaction owl_timer_irq = {
> >> + .name = "owl-timer",
> >> + .flags = IRQF_TIMER,
> >> + .handler = owl_timer_interrupt,
> >> + .dev_id = &owl_clockevent,
> >> +};
> >> +
> >> +static int __init owl_timer_init(struct device_node *node)
> >> +{
> >> + const unsigned long rate = 24000000;
> >
> > Use DT, either use clock-frequency or a clock ref.
>
> Are clk drivers really available at this point? clock-frequency sounds
> more promising.

Yes they are. Have a look at the other drivers.

> >> + int irq1, ret;
> >> +
> >> + owl_timer_base = of_io_request_and_map(node, 0, "owl-timer");
> >> + if (IS_ERR(owl_timer_base)) {
> >> + pr_err("Can't map timer registers");
> >> + return -ENXIO;
> >
> > Why not PTR_ERR(owl_timer_base) ?
>
> Only one in-tree driver (sun5i) matches such an expression. Will change.

[ ... ]

> > Please factor out these calls into a function.
>
> Do you have something in particular in mind? Maybe ..._reset() for the
> first three?

Yes.

> >> +
> >> + sched_clock_register(owl_timer_sched_read, 32, rate);
> >> + clocksource_mmio_init(owl_timer_base + OWL_T0_VAL, node->name,
> >> + rate, 200, 32, clocksource_mmio_readl_up);
> >> +
> >> + writel(0, owl_timer_base + OWL_T1_CTL);
> >> + writel(0, owl_timer_base + OWL_T1_VAL);
> >> + writel(0, owl_timer_base + OWL_T1_CMP);
> >> +
> >> + ret = setup_irq(irq1, &owl_timer_irq);
> >> + if (ret) {
> >> + pr_warn("failed to setup irq %d\n", irq1);
> >> + return ret;
> >> + }
> >
> > s/setup_irq/request_irq/
>
> Care to explain? setup_irq has 32 hits vs. 28 for request_irq.

The function setup_irq takes an irqaction as parameter. That forces all the
drivers to declare a structure, so for a multiple platforms support (aka single
kernel image), there are multiple structures declaration for nothing. The
function request_irq allocates the structure and then call setup_irq.

So now, request_irq is used in place of setup_irq.

> >> +
> >> + owl_clockevent.cpumask = cpumask_of(0);
> >> + owl_clockevent.irq = irq1;
> >> +
> >> + clockevents_config_and_register(&owl_clockevent, rate,
> >> + 0xf, 0xffffffff);
> >> +
> >> + return 0;
> >> +}
> >> +CLOCKSOURCE_OF_DECLARE(owl, "actions,owl-timer", owl_timer_init);
>
> Do you spot anything functionally wrong in this driver? Despite adding
> this new driver, I am only getting the following additional earlycon output:
>
> [ 0.000029] sched_clock: 32 bits at 24MHz, resolution 41ns, wraps
> every 89478484971ns
> [ 0.007888] clocksource: timer: mask: 0xffffffff max_cycles:
> 0xffffffff, max_idle_ns: 79635851949 ns
> [ 0.017748] Console: colour dummy device 80x30
> [ 0.022243] Calibrating delay loop...
> [ 0.030895] random: fast init done
> [ 0.231021] random: crng init done
>
> For S900 I'm using the generic timer instead.

I don't get the issue, can you elaborate ?

Thanks

-- Daniel


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