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From:   Rob Clark <robdclark@gmail.com>
Date:   Mon, 6 Sep 2021 18:45:21 -0700
Message-ID: <CAF6AEGugB5QinhyOxvAiG_V40=mXS20nnqxgk71xe_fmm1iZsw@mail.gmail.com>
Subject: Re: [PATCH] drm/msm: Disable frequency clamping on a630
To:     Amit Pundir <amit.pundir@linaro.org>
Cc:     John Stultz <john.stultz@linaro.org>,
        Caleb Connolly <caleb.connolly@linaro.org>,
        Rob Clark <robdclark@chromium.org>,
        freedreno <freedreno@lists.freedesktop.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
        Jonathan Marek <jonathan@marek.ca>,
        David Airlie <airlied@linux.ie>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Sharat Masetty <smasetty@codeaurora.org>,
        Akhil P Oommen <akhilpo@codeaurora.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Jordan Crouse <jordan@cosmicpenguin.net>,
        Stephen Boyd <sboyd@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Sean Paul <sean@poorly.run>,
        open list <linux-kernel@vger.kernel.org>
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On Mon, Sep 6, 2021 at 12:58 PM Amit Pundir <amit.pundir@linaro.org> wrote:
>
> On Mon, 6 Sept 2021 at 21:54, Rob Clark <robdclark@gmail.com> wrote:
> >
> > On Mon, Sep 6, 2021 at 1:02 AM Amit Pundir <amit.pundir@linaro.org> wrote:
> > >
> > > On Sat, 4 Sept 2021 at 01:55, Rob Clark <robdclark@gmail.com> wrote:
> > > >
> > > > On Fri, Sep 3, 2021 at 12:39 PM John Stultz <john.stultz@linaro.org> wrote:
> > > > >
> > > > > On Thu, Jul 29, 2021 at 1:49 PM Rob Clark <robdclark@gmail.com> wrote:
> > > > > > On Thu, Jul 29, 2021 at 1:28 PM Caleb Connolly
> > > > > > <caleb.connolly@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@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.
> > > > >
> > > >
> > > > 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
>

One thing I thought of, which would be worth ruling out, is whether
this issue only occurs with freq changes immediately after resuming
the GPU, vs freq changes in general.  Could you try the below patch.
And if it "fixes" the issue, then try reducing the delay until you
start seeing GPU hangs again.

----------
diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
index 40c9fef457a4..278b85207ea3 100644
--- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
+++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
@@ -1513,6 +1513,8 @@ static int a6xx_pm_resume(struct msm_gpu *gpu)
  if (ret)
  return ret;

+ msleep(5);
+
  msm_devfreq_resume(gpu);

  a6xx_llc_activate(a6xx_gpu);
----------

BR,
-R

>
> >
> > 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