linux-kernel - Re: [RFC v2 1/1] drm/lima: Add optional devfreq support

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Message-ID: <CAFBinCAgzHJQpcf1WVQPkNXOq1ziXp7nx=ZAU9_2-VzA9hg-Yw@mail.gmail.com>
Date:   Tue, 31 Dec 2019 17:47:39 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     yuq825@...il.com, dri-devel@...ts.freedesktop.org, robh@...nel.org,
        tomeu.vizoso@...labora.com, airlied@...ux.ie,
        linux-kernel@...r.kernel.org, steven.price@....com,
        linux-rockchip@...ts.infradead.org, wens@...e.org,
        alyssa.rosenzweig@...labora.com, daniel@...ll.ch,
        linux-amlogic@...ts.infradead.org
Subject: Re: [RFC v2 1/1] drm/lima: Add optional devfreq support

Hi Robin,

On Tue, Dec 31, 2019 at 5:40 PM Robin Murphy <robin.murphy@....com> wrote:
>
> On 2019-12-31 2:17 pm, Martin Blumenstingl wrote:
> > Hi Robin,
> >
> > On Mon, Dec 30, 2019 at 1:47 AM Robin Murphy <robin.murphy@....com> wrote:
> >>
> >> On 2019-12-29 11:19 pm, Martin Blumenstingl wrote:
> >>> Hi Robin,
> >>>
> >>> On Sun, Dec 29, 2019 at 11:58 PM Robin Murphy <robin.murphy@....com> wrote:
> >>>>
> >>>> Hi Martin,
> >>>>
> >>>> On 2019-12-27 5:37 pm, Martin Blumenstingl wrote:
> >>>>> Most platforms with a Mali-400 or Mali-450 GPU also have support for
> >>>>> changing the GPU clock frequency. Add devfreq support so the GPU clock
> >>>>> rate is updated based on the actual GPU usage when the
> >>>>> "operating-points-v2" property is present in the board.dts.
> >>>>>
> >>>>> The actual devfreq code is taken from panfrost_devfreq.c and modified so
> >>>>> it matches what the lima hardware needs:
> >>>>> - a call to dev_pm_opp_set_clkname() during initialization because there
> >>>>>      are two clocks on Mali-4x0 IPs. "core" is the one that actually clocks
> >>>>>      the GPU so we need to control it using devfreq.
> >>>>> - locking when reading or writing the devfreq statistics because (unlike
> >>>>>      than panfrost) we have multiple PP and GP IRQs which may finish jobs
> >>>>>      concurrently.
> >>>>
> >>>> I gave this a quick try on my RK3328, and the clock scaling indeed kicks
> >>>> in nicely on the glmark2 scenes that struggle, however something appears
> >>>> to be missing in terms of regulator association, as the appropriate OPP
> >>>> voltages aren't reflected in the GPU supply (fortunately the initial
> >>>> voltage seems close enough to that of the highest OPP not to cause major
> >>>> problems, on my box at least). With panfrost on RK3399 I do see the
> >>>> supply voltage scaling accordingly, but I don't know my way around
> >>>> devfreq well enough to know what matters in the difference :/
> >>> first of all: thank you for trying this out! :-)
> >>>
> >>> does your kernel include commit 221bc77914cbcc ("drm/panfrost: Use
> >>> generic code for devfreq") for your panfrost test?
> >>> if I understand the devfreq API correct then I suspect with that
> >>> commit panfrost also won't change the voltage anymore.
> >>
> >> Oh, you're quite right - I was already considering that change as
> >> ancient history, but indeed it's only in 5.5-rc, while that board is
> >> still on 5.4.y release kernels. No wonder I couldn't make sense of how
> >> the (current) code could possibly be working :)
> >>
> >> I'll try the latest -rc kernel tomorrow to confirm (now that PCIe is
> >> hopefully fixed), but I'm already fairly confident you've called it
> >> correctly.
> > I just tested it with the lima driver (by undervolting the GPU by
> > 0.05V) and it seems that dev_pm_opp_set_regulators is really needed.
> > I'll fix this in the next version of this patch and also submit a fix
> > for panfrost (I won't be able to test that though, so help is
> > appreciated in terms of testing :))
>
> Yeah, I started hacking something up for panfrost yesterday, but at the
> point of realising the core OPP code wants refactoring to actually
> handle optional regulators without spewing errors, decided that was
> crossing the line into "work" and thus could wait until next week :D
I'm not sure what you mean, dev_pm_opp_set_regulators uses
regulator_get_optional.
doesn't that mean that it is optional already?


Martin