linux-kernel - Re: [PATCH v4 10/11] drivers: perf: hisi: Handle counter overflow IRQ in MN PMU

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Date:   Fri, 24 Feb 2017 08:34:44 +0530
From:   Anurup M <anurupvasu@...il.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     will.deacon@....com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, anurup.m@...wei.com,
        zhangshaokun@...ilicon.com, tanxiaojun@...wei.com,
        xuwei5@...ilicon.com, sanil.kumar@...ilicon.com,
        john.garry@...wei.com, gabriele.paoloni@...wei.com,
        shiju.jose@...wei.com, huangdaode@...ilicon.com,
        linuxarm@...wei.com, Dikshit N <dikshit.n@...wei.com>,
        shyju.pv@...wei.com, "majun (Euler7)" <majun258@...wei.com>
Subject: Re: [PATCH v4 10/11] drivers: perf: hisi: Handle counter overflow IRQ
 in MN PMU

Sorry for delay in reply.

On Tuesday 21 February 2017 05:33 PM, Mark Rutland wrote:
> On Tue, Feb 21, 2017 at 05:19:58PM +0530, Anurup M wrote:
>> On Monday 20 February 2017 04:59 PM, Mark Rutland wrote:
>>> On Sun, Feb 19, 2017 at 01:51:22PM -0500, Anurup M wrote:
>>>> +			/* Clear the IRQ status flag */
>>>> +			hisi_djtag_writereg(module_id, MN1_BANK_SELECT,
>>>> +				MN1_INTC_REG_OFF, (1 << bit_pos), client);
>>>> +
>>>> +			/* Get the corresponding event struct */
>>>> +			event = mn_pmu->hw_perf_events[bit_pos];
>>>> +			if (!event)
>>>> +				continue;
>>> Do we expect to take interrupts for an event which does not exist?
>> Here I ignore if the event does not exist. I have seen it is handled
>> in arm_pmu and other reference
>> implementations to ignore if there is no event.
>> The event is cleared in .del. So if .del is called before the IRQ
>> handler, this check is required right?
>> Please comment.
> If there's a particular case whre we'd see the overflow bit set for an
> event, please add a comment describing that case here.
>
> [...]

Sure. I will do that.

>>>> +static int hisi_mn_init_irqs_fdt(struct device *dev,
>>>> +				struct hisi_pmu *mn_pmu)
>>>> +{
>>>> +	struct hisi_mn_data *mn_data = mn_pmu->hwmod_data;
>>>> +	struct hisi_djtag_client *client = mn_data->client;
>>>> +	int irq = -1, num_irqs, i;
>>>> +
>>>> +	num_irqs = of_irq_count(dev->of_node);
>>> Surely we expect a specific number of interrupts?
>>>
>>>> +	for (i = 0; i < num_irqs; i++) {
>>>> +		irq = of_irq_get(dev->of_node, i);
>>>> +		if (irq < 0)
>>>> +			dev_info(dev, "No IRQ resource!\n");
>>>> +	}
>>> Why are we throwing these away?
>>>
>>>> +
>>>> +	if (irq < 0)
>>>> +		return 0;
>>>> +
>>>> +	/* The last entry in the IRQ list to be chosen
>>>> +	 * This is as per mbigen-v2 IRQ mapping
>>>> +	 */
>>>> +	return hisi_mn_init_irq(irq, mn_pmu, client);
>>> I don't understand this comment.
>>>
>>> Why do we only use the list IRQ?
>>>
>>> What does this have to do with the mbigen?
>>>
>>> No ordering requirement was described in the DT binding.
>> There is a defect in the mbigen hardware to handle the IRQ mapping
>> for MN.
>> Due to this the IRQ property
>> of MN is made as a list and we read all IRQs and use only the last one.
>> I shall mention it in the comment and also add note in the DT bindings.
> You'll need to elaborate on that a bit further; I don't understand.
>
> If the interrupts aren't usable, there's arguably not much point listing
> them in the DT.
>
> Regardless, the order of the list *must* be specified in the DT binding.

I'm sorry for creating this confusion. It was a wrong workaround due to 
my misunderstanding of the
IRQ mapping.
The MN will use a single IRQ for overflow in HiP07. I shall update it 
and resend.
But in HiP05/06 there is no support for this IRQ, So I shall modify to 
use polling when IRQ is not available.

Thanks,
Anurup

> Thanks,
> Mark.