linux-kernel - Re: [PATCH] drm/msm: Disable frequency clamping on a630

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Date:   Thu, 29 Jul 2021 13:53:17 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Caleb Connolly <caleb.connolly@...aro.org>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Rob Clark <robdclark@...omium.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jordan Crouse <jordan@...micpenguin.net>,
        Jonathan Marek <jonathan@...ek.ca>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Sharat Masetty <smasetty@...eaurora.org>,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        open list <linux-kernel@...r.kernel.org>,
        Stephen Boyd <sboyd@...nel.org>
Subject: Re: [PATCH] drm/msm: Disable frequency clamping on a630

On Thu, Jul 29, 2021 at 1:28 PM Caleb Connolly
<caleb.connolly@...aro.org> wrote:
>
>
>
> On 29/07/2021 21:24, Rob Clark wrote:
> > On Thu, Jul 29, 2021 at 1:06 PM Caleb Connolly
> > <caleb.connolly@...aro.org> wrote:
> >>
> >> Hi Rob,
> >>
> >> I've done some more testing! It looks like before that patch ("drm/msm: Devfreq tuning") the GPU would never get above
> >> the second frequency in the OPP table (342MHz) (at least, not in glxgears). With the patch applied it would more
> >> aggressively jump up to the max frequency which seems to be unstable at the default regulator voltages.
> >
> > *ohh*, yeah, ok, that would explain it
> >
> >> Hacking the pm8005 s1 regulator (which provides VDD_GFX) up to 0.988v (instead of the stock 0.516v) makes the GPU stable
> >> at the higher frequencies.
> >>
> >> Applying this patch reverts the behaviour, and the GPU never goes above 342MHz in glxgears, losing ~30% performance in
> >> glxgear.
> >>
> >> I think (?) that enabling CPR support would be the proper solution to this - that would ensure that the regulators run
> >> at the voltage the hardware needs to be stable.
> >>
> >> Is hacking the voltage higher (although ideally not quite that high) an acceptable short term solution until we have
> >> CPR? Or would it be safer to just not make use of the higher frequencies on a630 for now?
> >>
> >
> > tbh, I'm not sure about the regulator stuff and CPR.. Bjorn is already
> > on CC and I added sboyd, maybe one of them knows better.
> >
> > In the short term, removing the higher problematic OPPs from dts might
> > be a better option than this patch (which I'm dropping), since there
> > is nothing stopping other workloads from hitting higher OPPs.
> Oh yeah that sounds like a more sensible workaround than mine .
> >
> > I'm slightly curious why I didn't have problems at higher OPPs on my
> > c630 laptop (sdm850)
> Perhaps you won the sillicon lottery - iirc sdm850 is binned for higher clocks as is out of the factory.
>
> Would it be best to drop the OPPs for all devices? Or just those affected? I guess it's possible another c630 might
> crash where yours doesn't?

I've not heard any reports of similar issues from the handful of other
folks with c630's on #aarch64-laptops.. but I can't really say if that
is luck or not.

Maybe just remove it for affected devices?  But I'll defer to Bjorn.

BR,
-R