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

[Amit Pundir]

On Mon, 6 Sept 2021 at 21:54, Rob Clark <robdclark@xxxxxxxxx> wrote:
>
> On Mon, Sep 6, 2021 at 1:02 AM Amit Pundir <amit.pundir@xxxxxxxxxx> wrote:
> >
> > On Sat, 4 Sept 2021 at 01:55, Rob Clark <robdclark@xxxxxxxxx> wrote:
> > >
> > > On Fri, Sep 3, 2021 at 12:39 PM John Stultz <john.stultz@xxxxxxxxxx> wrote:
> > > >
> > > > On Thu, Jul 29, 2021 at 1:49 PM Rob Clark <robdclark@xxxxxxxxx> wrote:
> > > > > On Thu, Jul 29, 2021 at 1:28 PM Caleb Connolly
> > > > > <caleb.connolly@xxxxxxxxxx> wrote:
> > > > > > On 29/07/2021 21:24, Rob Clark wrote:
> > > > > > > On Thu, Jul 29, 2021 at 1:06 PM Caleb Connolly
> > > > > > > <caleb.connolly@xxxxxxxxxx> 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'?
> >
> > I can reproduce this hard crash
> > https://www.irccloud.com/pastebin/Cu6UJntE/ and a gpu lockup
> > https://www.irccloud.com/pastebin/6Ryd2Pug/ at times reliably, by
> > running antutu benchmark on pocof1.
> >
> > Reverting 9bc95570175a ("drm/msm: Devfreq tuning") helps and I no
> > longer see these errors.
> >
> > Complete dmesg for hardcrash https://pastebin.com/raw/GLZVQFQN
> >
>
> Does antutu trigger this issue as easily on db845c?  If no, does
> db845c have pmic differences compared to pocof1 and Caleb's phone?

Yes I can reproduce this hard crash with antutu on db845c as well with
linux/master at 477f70cd2a67 ("Merge tag 'drm-next-2021-08-31-1' of
git://anongit.freedesktop.org/drm/drm").

Dmesg: https://pastebin.com/raw/xXtvxk0G


>
> I think we may need some help from qcom here, but I'll go back and
> look at older downstream kernels to see if I can find any evidence
> that we need to limit how far we change the freq in a single step.
> It's not clear to me if there is some physical constraint that the
> driver needs to respect, or if we have some missing/incorrect
> configuration for a630.  IIRC the downstream kernel is letting the GMU
> do more of the freq management, so it might be handling this case for
> the kernel.  But the GMU is a bit of a black box to me and I don't
> have any docs, so just a guess.
>
> It would be helpful if someone who can repro this could try the
> experiments I mentioned about increasing min_freq and/or decreasing
> max_freq to limit the size of the freq change until the issue does not
> happen.
>
> If we have to, we can merge this hack patch to disable freq clamping
> on a630.. but that isn't really a fix.  The root issue is a power
> issue, 9bc95570175a just made it more likely to see the problem.
>
> BR,
> -R
>
> > Regards,
> > Amit Pundir
> >
> > >
> > > 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