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

[Rob Clark]

On Thu, Sep 9, 2021 at 12:50 PM Akhil P Oommen <akhilpo@xxxxxxxxxxxxxx> wrote:
>
> On 9/9/2021 9:42 PM, Amit Pundir wrote:
> > On Thu, 9 Sept 2021 at 17:47, Amit Pundir <amit.pundir@xxxxxxxxxx> wrote:
> >>
> >> On Wed, 8 Sept 2021 at 07:50, Bjorn Andersson
> >> <bjorn.andersson@xxxxxxxxxx> wrote:
> >>>
> >>> On Mon 09 Aug 10:26 PDT 2021, Akhil P Oommen wrote:
> >>>
> >>>> On 8/9/2021 9:48 PM, Caleb Connolly wrote:
> >>>>>
> >>>>>
> >>>>> On 09/08/2021 17:12, Rob Clark wrote:
> >>>>>> On Mon, Aug 9, 2021 at 7:52 AM Akhil P Oommen
> >>>>>> <akhilpo@xxxxxxxxxxxxxx> wrote:
> >>> [..]
> >>>>>>> I am a bit confused. We don't define a power domain for gpu in dt,
> >>>>>>> correct? Then what exactly set_opp do here? Do you think this usleep is
> >>>>>>> what is helping here somehow to mask the issue?
> >>>>> The power domains (for cx and gx) are defined in the GMU DT, the OPPs in
> >>>>> the GPU DT. For the sake of simplicity I'll refer to the lowest
> >>>>> frequency (257000000) and OPP level (RPMH_REGULATOR_LEVEL_LOW_SVS) as
> >>>>> the "min" state, and the highest frequency (710000000) and OPP level
> >>>>> (RPMH_REGULATOR_LEVEL_TURBO_L1) as the "max" state. These are defined in
> >>>>> sdm845.dtsi under the gpu node.
> >>>>>
> >>>>> The new devfreq behaviour unmasks what I think is a driver bug, it
> >>>>> inadvertently puts much more strain on the GPU regulators than they
> >>>>> usually get. With the new behaviour the GPU jumps from it's min state to
> >>>>> the max state and back again extremely rapidly under workloads as small
> >>>>> as refreshing UI. Where previously the GPU would rarely if ever go above
> >>>>> 342MHz when interacting with the device, it now jumps between min and
> >>>>> max many times per second.
> >>>>>
> >>>>> If my understanding is correct, the current implementation of the GMU
> >>>>> set freq is the following:
> >>>>>    - Get OPP for frequency to set
> >>>>>    - Push the frequency to the GMU - immediately updating the core clock
> >>>>>    - Call dev_pm_opp_set_opp() which triggers a notify chain, this winds
> >>>>> up somewhere in power management code and causes the gx regulator level
> >>>>> to be updated
> >>>>
> >>>> Nope. dev_pm_opp_set_opp() sets the bandwidth for gpu and nothing else. We
> >>>> were using a different api earlier which got deprecated -
> >>>> dev_pm_opp_set_bw().
> >>>>
> >>>
> >>> On the Lenovo Yoga C630 this is reproduced by starting alacritty and if
> >>> I'm lucky I managed to hit a few keys before it crashes, so I spent a
> >>> few hours looking into this as well...
> >>>
> >>> As you say, the dev_pm_opp_set_opp() will only cast a interconnect vote.
> >>> The opp-level is just there for show and isn't used by anything, at
> >>> least not on 845.
> >>>
> >>> Further more, I'm missing something in my tree, so the interconnect
> >>> doesn't hit sync_state, and as such we're not actually scaling the
> >>> buses. So the problem is not that Linux doesn't turn on the buses in
> >>> time.
> >>>
> >>> So I suspect that the "AHB bus error" isn't saying that we turned off
> >>> the bus, but rather that the GPU becomes unstable or something of that
> >>> sort.
> >>>
> >>>
> >>> Lastly, I reverted 9bc95570175a ("drm/msm: Devfreq tuning") and ran
> >>> Aquarium for 20 minutes without a problem. I then switched the gpu
> >>> devfreq governor to "userspace" and ran the following:
> >>>
> >>> while true; do
> >>>    echo 257000000 > /sys/class/devfreq/5000000.gpu/userspace/set_freq
> >>>    echo 710000000 > /sys/class/devfreq/5000000.gpu/userspace/set_freq
> >>> done
> >>>
> >>> It took 19 iterations of this loop to crash the GPU.
> >>
> >> Ack. With your above script, I can reproduce a crash too on db845c
> >> (A630) running v5.14. I didn't get any crash log though and device
> >> just rebooted to USB crash mode.
> >>
> >> And same crash on RB5 (A650) too https://hastebin.com/raw/ejutetuwun
>
> Are we sure this is the same issue? It could be, but I thought we were
> seeing a bunch of random gpu errors (which may eventually hit device crash).

In the sense that async-serror often seems to be a clk issue, it
*could* be related.. but this would have to be triggered by CPU
access.  The symptom does seem very different.

BR,
-R

> -Akhil
>
> >
> > fwiw I can't reproduce this crash on RB5 so far with v5.15-rc1 merge
> > window (HEAD: 477f70cd2a67)
> >
> >>
> >>>
> >>> So the problem doesn't seem to be Rob's change, it's just that prior to
> >>> it the chance to hitting it is way lower. Question is still what it is
> >>> that we're triggering.
> >>>
> >>> Regards,
> >>> Bjorn
>