linux-kernel - Re: [PATCH v6 08/11] drivers: perf: hisi: use poll method to avoid L3C counter overflow

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Date:   Mon, 27 Mar 2017 12:03:24 +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@...wei.com, shyju.pv@...wei.com
Subject: Re: [PATCH v6 08/11] drivers: perf: hisi: use poll method to avoid
 L3C counter overflow



On Friday 24 March 2017 05:13 PM, Mark Rutland wrote:
>>> How do we ensure that we don't take the interrupt in the middle of a
>>> > >sequence of accesses to the HW?
>> >
>> >The L3 cache and MN PMU does not use the overflow IRQ and it does
>> >not occur here
>> >as the interrupt Mask register is by default masked in hardware.
> I was referring to the timer interrupt which backs the hrtimer.
>
> i.e. how do we guarantee that hisi_hrtimer_callback() is not called
> while we are in the middle of a RMW sequence? Are interrupts disabled
> for all of those seqeunces?

The HW access via djtag read and write are protected by spin_lock_irqsave.

Thanks,
Anurup

> Thanks,
> Mark.