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Date: Tue, 1 Nov 2016 09:03:32 +0000
From: Noam Camus <noamca@...lanox.com>
To: Thomas Gleixner <tglx@...utronix.de>
CC: "robh+dt@...nel.org" <robh+dt@...nel.org>,
"mark.rutland@....com" <mark.rutland@....com>,
"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Chris Metcalf <cmetcalf@...lanox.com>
Subject: RE: [PATCH v3 3/3] clocksource: Add clockevent support to NPS400
driver
> From: Thomas Gleixner [mailto:tglx@...utronix.de]
> Sent: Monday, October 31, 2016 8:13 PM
>>
>> -static unsigned long nps_timer_rate;
>> +static unsigned long nps_timer1_freq;
>This should be either in the previous patch or seperate.
Will fix in V4
....
>> @@ -101,3 +101,215 @@ static int __init nps_setup_clocksource(struct
>> device_node *node)
>>
>> CLOCKSOURCE_OF_DECLARE(ezchip_nps400_clksrc, "ezchip,nps400-timer",
>> nps_setup_clocksource);
>> +CLOCKSOURCE_OF_DECLARE(ezchip_nps400_clk_src, "ezchip,nps400-timer1",
>> + nps_setup_clocksource);
>What's the point of this change?
I do this as preparation for next patch where we use timer0 for clockevent while timer1 is kept for clocksource.
I realize that it is not aligned with binding document, so I will move this to next patch.
>> +/*
>> + * Arm the timer to interrupt after @cycles */ static void
>> +nps_clkevent_timer_event_setup(unsigned int cycles) {
>> + write_aux_reg(NPS_REG_TIMER0_LIMIT, cycles);
>> + write_aux_reg(NPS_REG_TIMER0_CNT, 0); /* start from 0 */
>Please do not use tail comments. They break the reading flow.
Will fix in V4
>> +
>> + write_aux_reg(NPS_REG_TIMER0_CTRL, TIMER0_CTRL_IE | TIMER0_CTRL_NH);
>> +}
>> +
>> +static void nps_clkevent_rm_thread(bool remove_thread)
>I have a hard time to understand why a remove_thread function needs a remove_thread boolean argument. Commenting things like this would be more helpful than commenting the obvious.
Sorry for that, will be commented in V4
>> +{
>> + unsigned int cflags;
>> + unsigned int enabled_threads;
>>+ unsigned long flags;
>> + int thread;
>> +
>> + local_irq_save(flags);
>That's pointless. Both call sites have interrupts disabled.
Will be fixed in V4
...
>> +
>> +static void nps_clkevent_add_thread(bool set_event) {
>> + int thread;
>> + unsigned int cflags, enabled_threads;
>> + unsigned long flags;
>> +
>> + local_irq_save(flags);
>Ditto.
Will be removed as well at V4
...
>> +static int nps_clkevent_set_next_event(unsigned long delta,
>> + struct clock_event_device *dev) {
>> + struct irq_desc *desc = irq_to_desc(nps_timer0_irq);
>> + struct irq_chip *chip = irq_data_get_irq_chip(&desc->irq_data);
>> +
>> + nps_clkevent_add_thread(true);
>> + chip->irq_unmask(&desc->irq_data);
>Oh no. You are not supposed to fiddle in the guts of the interrupts from a random driver. Can you please explain what you are trying to do and why >the existing interfaces are not sufficient?
This function is assigned and used by several hooks at clock_event_device type.
Main purpose is to support oneshot timer mode and in general support NOHZ_FULL and finally TASK_ISOLATION.
The idea for this is borrowed from arch/tile timer driver that just like us aiming to support the TASK_ISOLATION.
Will it be better to replace these with irq_percpu_enable()/irq_percpu_disable() which seem to achieve quiet the same affect?
...
>> +static int nps_clkevent_set_periodic(struct clock_event_device *dev)
>> +{
>> + nps_clkevent_add_thread(false);
>> + if (read_aux_reg(CTOP_AUX_THREAD_ID) == 0)
>> + nps_clkevent_timer_event_setup(nps_timer0_freq / HZ);
>So how is that enabling interrupts again?
I guess that in our system we never switch back to periodic.
Time infrastructure starts as periodic (I set CLOCK_EVT_FEAT_PERIODIC) and when timer is ready
state is switched to oneshot mode and never goes back to periodic.
I might be missing here, but couldn't find any place where CLOCK_EVT_STATE_PERIODIC is set but in tick_setup_periodic().
Should I call here to enable interrupts anyway?
>> +
>> +static irqreturn_t timer_irq_handler(int irq, void *dev_id) {
>> + /*
>> + * Note that generic IRQ core could have passed @evt for @dev_id if
>> + * irq_set_chip_and_handler() asked for handle_percpu_devid_irq()
>
>And why are you not doing that?
Will do that in V4
>> +static int __init nps_setup_clockevent(struct device_node *node) {
>> + struct clock_event_device *evt = this_cpu_ptr(&nps_clockevent_device);
>> + struct clk *clk;
>> + int ret;
>> +
>> + nps_timer0_irq = irq_of_parse_and_map(node, 0);
>> + if (nps_timer0_irq <= 0) {
>> + pr_err("clockevent: missing irq");
>> + return -EINVAL;
>> + }
>> +
>> + nps_get_timer_clk(node, &nps_timer0_freq, clk);
>> +
>> + /* Needs apriori irq_set_percpu_devid() done in intc map function */
>> + ret = request_percpu_irq(nps_timer0_irq, timer_irq_handler,
>> + "Timer0 (per-cpu-tick)", evt);
>
>This is wrong. the dev_id argument wants to be a __per_cpu pointer. So it should be &nps_clockevent_device and not a pointer to the cpu local one.
Will fix that in V4
>> + if (ret) {
>> + pr_err("Couldn't request irq\n");
>> + clk_disable_unprepare(clk);
>> + return ret;
>> + }
>> +
>> + ret = cpuhp_setup_state(CPUHP_AP_NPS_TIMER_STARTING,
>> + "AP_NPS_TIMER_STARTING",
>
>Please make this "clockevents/nps:starting"
Sorry but I can't see any similar thing all around.
Could you explain why you prefer this format for the string?
>> + nps_timer_starting_cpu,
>> + nps_timer_dying_cpu);
>> + if (ret) {
>> + pr_err("Failed to setup hotplug state");
>> + clk_disable_unprepare(clk);
>
>You leave the irq requested....
Will fix that in V4.
Many thanks for all comments.
Waiting for your answers on my few questions above.
-Noam
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