linux-kernel - Re: [PATCH v2 4/4] interconnect: qcom: icc-rpmh: Add BCMs to commit list in pre

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Date:   Wed, 11 Aug 2021 11:13:44 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Alex Elder <elder@...aro.org>,
        Mike Tipton <mdtipton@...eaurora.org>, djakov@...nel.org
Cc:     bjorn.andersson@...aro.org, agross@...nel.org,
        saravanak@...gle.com, okukatla@...eaurora.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2 4/4] interconnect: qcom: icc-rpmh: Add BCMs to commit
 list in pre_aggregate

Quoting Alex Elder (2021-08-11 09:01:27)
> On 8/10/21 6:31 PM, Stephen Boyd wrote:
> > Quoting Mike Tipton (2021-07-21 10:54:32)
> >> We're only adding BCMs to the commit list in aggregate(), but there are
> >> cases where pre_aggregate() is called without subsequently calling
> >> aggregate(). In particular, in icc_sync_state() when a node with initial
> >> BW has zero requests. Since BCMs aren't added to the commit list in
> >> these cases, we don't actually send the zero BW request to HW. So the
> >> resources remain on unnecessarily.
> >>
> >> Add BCMs to the commit list in pre_aggregate() instead, which is always
> >> called even when there are no requests.
> >>
> >> Fixes: 976daac4a1c5 ("interconnect: qcom: Consolidate interconnect RPMh support")
> >> Signed-off-by: Mike Tipton <mdtipton@...eaurora.org>
> >> ---
> >
> > This patch breaks reboot for me on sc7180 Lazor
>
> If I am using the interface improperly or something in the
> IPA driver, please let me know.  I actually plan to switch
> to using the bulk interfaces soon (FYI).
>

I suspect I'm seeing a shutdown ordering issue, where we start dropping
interconnect requests in driver shutdown callbacks and then some bus
turns off and the CPU can't access a device. Maybe to fix this problem
(if reverting isn't an option) would be to add a shutdown hook to
rpmh-icc that effectively "props up" the bandwidth requests during
shutdown so that we don't have to think about finding the place that the
interconnect is turned off. We're shutting down/restarting anyway, so
there isn't much point in trying to be power efficient for the last few
moments of runtime.