Re: [PATCH 0/5] clk/qcom: Support gdsc collapse polling using 'reset' inteface

[Akhil P Oommen]

On 8/3/2022 12:02 AM, Rob Clark wrote:
> On Tue, Aug 2, 2022 at 12:02 AM Dmitry Baryshkov
> <dmitry.baryshkov@xxxxxxxxxx> wrote:
> > On 30/07/2022 12:17, Akhil P Oommen wrote:
> > > Some clients like adreno gpu driver would like to ensure that its gdsc
> > > is collapsed at hardware during a gpu reset sequence. This is because it
> > > has a votable gdsc which could be ON due to a vote from another subsystem
> > > like tz, hyp etc or due to an internal hardware signal.
> > If this is votable, do we have any guarantee that the gdsc will collapse
> > at all? How can we proceed if it did not collapse?
> Other potential votes should be transient.  But I guess we eventually
> need to timeout and give up.  At which point we are no worse off than
> before.
>
> But hmm, we aren't using RBBM_SW_RESET_CMD for sw reset like we have
> on previous generations?  That does seem a bit odd.  Looks like kgsl
> does use it.
>
> BR,
> -R
Like Rob mentioned there could be transient votes from other 
clients/subsystem. It could be even stuck ON when hardware is in bad 
shape in some very rare cases. For the worst case scenario, I have added 
a timeout (500msec) in the gdsc reset op.

I have added the Soft reset in [1]. But this resets only the core gpu 
blocks, not everything. For eg. GMU.

[1] [PATCH v3 7/8] drm/msm/a6xx: Improve gpu recovery sequence

> > > To allow
> > > this, gpucc driver can expose an interface to the client driver using
> > > reset framework. Using this the client driver can trigger a polling within
> > > the gdsc driver.
> > Trigger the polling made me think initially that we will actually
> > trigger something in the HW. Instead the client uses reset framework to
> > poll for the gdsc to be reset.
Yes. I should replace 'trigger' with 'start' here.

-Akhil.
> > > This series is rebased on top of linus's master branch.
> > >
> > > Related discussion: https://patchwork.freedesktop.org/patch/493144/
> > >
> > >
> > > Akhil P Oommen (5):
> > >     dt-bindings: clk: qcom: Support gpu cx gdsc reset
> > >     clk: qcom: Allow custom reset ops
> > >     clk: qcom: gpucc-sc7280: Add cx collapse reset support
> > >     clk: qcom: gdsc: Add a reset op to poll gdsc collapse
> > >     arm64: dts: qcom: sc7280: Add Reset support for gpu
> > >
> > >    arch/arm64/boot/dts/qcom/sc7280.dtsi          |  3 +++
> > >    drivers/clk/qcom/gdsc.c                       | 23 +++++++++++++++++++----
> > >    drivers/clk/qcom/gdsc.h                       |  7 +++++++
> > >    drivers/clk/qcom/gpucc-sc7280.c               |  6 ++++++
> > >    drivers/clk/qcom/reset.c                      |  6 ++++++
> > >    drivers/clk/qcom/reset.h                      |  2 ++
> > >    include/dt-bindings/clock/qcom,gpucc-sc7280.h |  3 +++
> > >    7 files changed, 46 insertions(+), 4 deletions(-)
> >
> > --
> > With best wishes
> > Dmitry