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

[Robin Murphy]

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@xxxxxxx> 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.

Cheers,
Robin.

> this is probably due to a missing call to dev_pm_opp_set_regulators()
> which is supposed to attach the regulator to the devfreq instance.
> I didn't notice this yet because on Amlogic SoCs the voltage is the
> same for all OPPs.
>
> I'll debug this in the next days and send an updated patch (and drop
> the RFC prefix if there are no more comments).
>
>
> Regards
> Martin