[PATCH] drm/msm: Disable frequency clamping on a630

[John Stultz]

On Thu, Jul 29, 2021 at 1:49 PM Rob Clark <robdclark at gmail.com> wrote:
> On Thu, Jul 29, 2021 at 1:28 PM Caleb Connolly
> <caleb.connolly at linaro.org> wrote:
> > On 29/07/2021 21:24, Rob Clark wrote:
> > > On Thu, Jul 29, 2021 at 1:06 PM Caleb Connolly
> > > <caleb.connolly at linaro.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.

thanks
-john