Re: [PATCH] arm64: dts: allwinner: a64: Drop PMU node

[Vasily Khoruzhick <anarsoul@gmail.com>]

On Mon, Sep 23, 2019 at 4:51 PM Vasily Khoruzhick <anarsoul@gmail.com> wrote:
>
> On Mon, Aug 12, 2019 at 10:39 PM Maxime Ripard
> <maxime.ripard@bootlin.com> wrote:
> >
> > On Mon, Aug 12, 2019 at 11:01:51AM -0700, Vasily Khoruzhick wrote:
> > > On Mon, Aug 12, 2019 at 1:04 AM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
> > > >
> > > > On Thu, Aug 08, 2019 at 12:59:07PM -0700, Vasily Khoruzhick wrote:
> > > > > On Thu, Aug 8, 2019 at 9:26 AM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
> > > > > >
> > > > > > On Wed, Aug 07, 2019 at 10:36:08AM -0700, Vasily Khoruzhick wrote:
> > > > > > > On Wed, Aug 7, 2019 at 4:56 AM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
> > > > > > > >
> > > > > > > > On Tue, Aug 06, 2019 at 07:39:26PM -0700, Vasily Khoruzhick wrote:
> > > > > > > > > On Tue, Aug 6, 2019 at 2:14 PM Robin Murphy <robin.murphy@arm.com> wrote:
> > > > > > > > > >
> > > > > > > > > > On 2019-08-06 9:52 pm, Vasily Khoruzhick wrote:
> > > > > > > > > > > On Tue, Aug 6, 2019 at 1:19 PM Harald Geyer <harald@ccbib.org> wrote:
> > > > > > > > > > >>
> > > > > > > > > > >> Vasily Khoruzhick writes:
> > > > > > > > > > >>> On Tue, Aug 6, 2019 at 7:35 AM Robin Murphy <robin.murphy@arm.com> wrote:
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> On 06/08/2019 15:01, Vasily Khoruzhick wrote:
> > > > > > > > > > >>>>> Looks like PMU in A64 is broken, it generates no interrupts at all and
> > > > > > > > > > >>>>> as result 'perf top' shows no events.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> Does something like 'perf stat sleep 1' at least count cycles correctly?
> > > > > > > > > > >>>> It could well just be that the interrupt numbers are wrong...
> > > > > > > > > > >>>
> > > > > > > > > > >>> Looks like it does, at least result looks plausible:
> > > > > > > > > > >>
> > > > > > > > > > >> I'm using perf stat regularly (cache benchmarks) and it works fine.
> > > > > > > > > > >>
> > > > > > > > > > >> Unfortunately I wasn't aware that perf stat is a poor test for
> > > > > > > > > > >> the interrupts part of the node, when I added it. So I'm not too
> > > > > > > > > > >> surprised I got it wrong.
> > > > > > > > > > >>
> > > > > > > > > > >> However, it would be unfortunate if the node got removed completely,
> > > > > > > > > > >> because perf stat would not work anymore. Maybe we can only remove
> > > > > > > > > > >> the interrupts or just fix them even if the HW doesn't work?
> > > > > > > > > > >
> > > > > > > > > > > I'm not familiar with PMU driver. Is it possible to get it working
> > > > > > > > > > > without interrupts?
> > > > > > > > > >
> > > > > > > > > > Yup - you get a grumpy message from the driver, it will refuse sampling
> > > > > > > > > > events (the ones which weren't working anyway), and if you measure
> > > > > > > > > > anything for long enough that a counter overflows you'll get wonky
> > > > > > > > > > results. But for counting hardware events over relatively short periods
> > > > > > > > > > it'll still do the job.
> > > > > > > > >
> > > > > > > > > I tried to drop interrupts completely from the node but 'perf top' is
> > > > > > > > > still broken. Though now in different way: it complains "cycles: PMU
> > > > > > > > > Hardware doesn't support sampling/overflow-interrupts. Try 'perf
> > > > > > > > > stat'"
> > > > > > > >
> > > > > > > > I have no idea if that's the culprit, but what is the state of the
> > > > > > > > 0x09010000 register?
> > > > > > >
> > > > > > > What register is that and how do I check it?
> > > > > >
> > > > > > It's in the CPUX Configuration block, and the bits are labelled as CPU
> > > > > > Debug Reset.
> > > > > >
> > > > > > And if you have busybox, you can use devmem.
> > > > >
> > > > > CPUX configuration block is at 0x01700000 according to A64 user
> > > > > manual, and particular register you're interested in is at 0x01700080,
> > > > > its value is 0x1110110F.
> > > > >
> > > > > Bits 16-19 are not defined in user manual and are not set.
> > > >
> > > > Sorry, I somehow thought this was for the H6...
> > > >
> > > > I don't have any idea then :/
> > >
> > > OK, so what should we do? 'perf top'/'perf record' work fine if PMU
> > > node is dropped, but they don't work if PMU node is present (even with
> > > interrupts dropped). I'd prefer to have 'perf top' and 'perf record'
> > > working instead of 'perf stat'
> >
> > Well, it doesn't work so we should just remove the node, and if
> > someone wants it back, they should figure it out.
>
> Hey Maxime,
>
> So can you merge this patch?

Added new Maxime's email to CC

> > Maxime
> >
> > --
> > Maxime Ripard, Bootlin
> > Embedded Linux and Kernel engineering
> > https://bootlin.com

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