linux-kernel - Re: [PATCH] drm/msm/adreno: adreno_gpu: Use suspend() instead of idle() on load error

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Message-ID: <CAA8EJpohEo+kMw7fx5112m+z7JHSLDmsqOL4T7hmyvr2fPP8vQ@mail.gmail.com>
Date:   Wed, 29 Mar 2023 22:45:52 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Johan Hovold <johan@...nel.org>, linux-arm-msm@...r.kernel.org,
        andersson@...nel.org, agross@...nel.org,
        marijn.suijten@...ainline.org, Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Johan Hovold <johan+linaro@...nel.org>,
        Akhil P Oommen <quic_akhilpo@...cinc.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Nathan Chancellor <nathan@...nel.org>,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/adreno: adreno_gpu: Use suspend() instead of
 idle() on load error

On Wed, 29 Mar 2023 at 18:48, Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
>
>
>
> On 29.03.2023 16:37, Johan Hovold wrote:
> > On Wed, Mar 29, 2023 at 04:04:44PM +0200, Konrad Dybcio wrote:
> >> If we fail to initialize the GPU for whatever reason (say we don't
> >> embed the GPU firmware files in the initrd), the error path involves
> >> pm_runtime_put_sync() which then calls idle() instead of suspend().
> >>
> >> This is suboptimal, as it means that we're not going through the
> >> clean shutdown sequence. With at least A619_holi, this makes the GPU
> >> not wake up until it goes through at least one more start-fail-stop
> >> cycle. Fix that by using pm_runtime_put_sync_suspend to force a clean
> >> shutdown.
> >
> > This does not sound right. If pm_runtime_put_sync() fails to suspend the
> > device when the usage count drops to zero, then you have a bug somewhere
> > else.
> I was surprised to see that it was not called as well, but I wasn't able
> to track it down before..

Could you please check that it's autosuspend who kicks in? In other
words, if we disable autosuspend, the pm_runtime_put_sync is enough()?

That would probably mean that we lack some kind of reset in the hw_init path.

On the other hand, I do not know how the device will react to the
error-in-the-middle state. Modems for example, can enter the state
where you can not properly turn it off once it starts the boot
process.

And if we remember the efforts that Akhil has put into making sure
that the GPU is properly reset in case of an _error_, it might be
nearly impossible to shut it down in a proper way.

Thus said, I think that unless there is an obvious way to restart the
init process, Korad's pm_runtime_put_sync_suspend() looks like a
correct fix to me.

> > Also since commit 2c087a336676 ("drm/msm/adreno: Load the firmware
> > before bringing up the hardware") the firmware is loaded before even
> > hitting these paths so the above description does not sound right in
> > that respect either (or is missing some details).
> ..but I did some more digging and I found that the precise "firmware"
> that fails is the ZAP blob, which is not checked like SQE in the
> commit you mentioned!
>
> Now I don't think that we can easily check for it as-is since
> zap_shader_load_mdt() does the entire find-load-authenticate
> dance which is required with secure assets, but it's obviously
> possible to rip out the find-load part of that and go on from
> there.

Yes, I think we should load all firmware early. ZAP shader is a bit
unique since the DT can override the name, but it might be nice to
check for its presence earlier.

At the same time it probably should not stop us from fixing the idle()
vs suspend() bug.

>
> Do you think that would be a better solution?
>
> Konrad
>
> >
> >> Test cases:
> >> 1. firmware baked into kernel
> >> 2. error loading fw in initrd -> load from rootfs at DE start
> >>
> >> Both succeed on A619_holi (SM6375) and A630 (SDM845).
> >>
> >> Fixes: 0d997f95b70f ("drm/msm/adreno: fix runtime PM imbalance at gpu load")
> >> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> >> ---
> >>  drivers/gpu/drm/msm/adreno/adreno_device.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/msm/adreno/adreno_device.c b/drivers/gpu/drm/msm/adreno/adreno_device.c
> >> index f61896629be6..59f3302e8167 100644
> >> --- a/drivers/gpu/drm/msm/adreno/adreno_device.c
> >> +++ b/drivers/gpu/drm/msm/adreno/adreno_device.c
> >> @@ -477,7 +477,7 @@ struct msm_gpu *adreno_load_gpu(struct drm_device *dev)
> >>      return gpu;
> >>
> >>  err_put_rpm:
> >> -    pm_runtime_put_sync(&pdev->dev);
> >> +    pm_runtime_put_sync_suspend(&pdev->dev);
> >>  err_disable_rpm:
> >>      pm_runtime_disable(&pdev->dev);
> >
> > Johan



-- 
With best wishes
Dmitry