Date:   Fri, 3 Sep 2021 13:29:09 -0700
From:   Rob Clark <robdclark@...il.com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Caleb Connolly <caleb.connolly@...aro.org>,
        Rob Clark <robdclark@...omium.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Jonathan Marek <jonathan@...ek.ca>,
        David Airlie <airlied@...ux.ie>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Sharat Masetty <smasetty@...eaurora.org>,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Jordan Crouse <jordan@...micpenguin.net>,
        Stephen Boyd <sboyd@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Sean Paul <sean@...rly.run>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm: Disable frequency clamping on a630

On Fri, Sep 3, 2021 at 12:39 PM John Stultz <john.stultz@...aro.org> wrote:
>
> On Thu, Jul 29, 2021 at 1:49 PM Rob Clark <robdclark@...il.com> wrote:
> > 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.
>
> Just as another datapoint, I was just marveling at how suddenly smooth
> the UI was performing on db845c and Caleb pointed me at the "drm/msm:
> Devfreq tuning" patch as the likely cause of the improvement, and
> mid-discussion my board crashed into USB crash mode:
> [  146.157696][    C0] adreno 5000000.gpu: CP | AHB bus error
> [  146.163303][    C0] adreno 5000000.gpu: CP | AHB bus error
> [  146.168837][    C0] adreno 5000000.gpu: RBBM | ATB bus overflow
> [  146.174960][    C0] adreno 5000000.gpu: CP | HW fault | status=0x00000000
> [  146.181917][    C0] adreno 5000000.gpu: CP | AHB bus error
> [  146.187547][    C0] adreno 5000000.gpu: CP illegal instruction error
> [  146.194009][    C0] adreno 5000000.gpu: CP | AHB bus error
> [  146.308909][    T9] Internal error: synchronous external abort:
> 96000010 [#1] PREEMPT SMP
> [  146.317150][    T9] Modules linked in:
> [  146.320941][    T9] CPU: 3 PID: 9 Comm: kworker/u16:1 Tainted: G
>     W         5.14.0-mainline-06795-g42b258c2275c #24
> [  146.331974][    T9] Hardware name: Thundercomm Dragonboar
> Format: Log Type - Time(microsec) - Message - Optional Info
> Log Type: B - Since Boot(Power On Reset),  D - Delta,  S - Statistic
> S - QC_IMAGE_VERSION_STRING=BOOT.XF.2.0-00371-SDM845LZB-1
> S - IMAGE_VARIANT_STRING=SDM845LA
> S - OEM_IMAGE_VERSION_STRING=TSBJ-FA-PC-02170
>
> So Caleb sent me to this thread. :)
>
> I'm still trying to trip it again, but it does seem like db845c is
> also seeing some stability issues with Linus' HEAD.
>

Caleb's original pastebin seems to have expired (or at least require
some sort of ubuntu login to access).. were the crashes he was seeing
also 'AHB bus error'?

If you have a reliable reproducer, I guess it would be worth seeing if
increasing the min_freq (ie. to limit how far we jump the freq in one
shot) "fixes" it?

I guess I could check downstream kgsl to see if they were doing
something to increase freq in smaller increments.. I don't recall that
they were but it has been a while since I dug thru that code.  And I
suppose downstream it could also be done in their custom tz governor.

BR,
-R

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