linux-kernel - Re: [PATCH v3] interconnect: qcom: icc-rpmh: Add BCMs to commit list in pre

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Date:   Mon, 11 Apr 2022 21:18:07 -0500
From:   Alex Elder <elder@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>, djakov@...nel.org,
        okukatla@...eaurora.org, quic_mdtipton@...cinc.com
Cc:     linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Mike Tipton <mdtipton@...eaurora.org>, mka@...omium.org,
        dianders@...omium.org
Subject: Re: [PATCH v3] interconnect: qcom: icc-rpmh: Add BCMs to commit list
 in pre_aggregate

On 4/11/22 2:06 PM, Stephen Boyd wrote:
>> The second problem you have is exhibited by the IPA driver if
>> the "fix" commit (upstream b95b668eaaa2) is back-ported to the
>> Linux 5.10.y LTS branch (along with some other prerequisite
>> commits).  We can conclude that applying the above commit
>> makes the bandwidth for an unused interconnect (or perhaps
>> the rate for the IPA core clock) get set to zero.  And in that
>> case, an attempt to access IPA hardware leads to the crash you
>> observed.
>>
>> The IPA driver does not implement runtime power management
>> until Linux v5.15.  You later said you thought enabling that
>> might ensure the clock and interconnects were active when
>> needed by the IPA driver, and I concur (but there could be a
>> little more to it).
> Is the runtime PM patch series necessary to enable the IPA clk and
> interconnects? Things don't look good on 5.10.y and I'm not sure it will
> be workable. Commit b1d681d8d324 ("interconnect: Add sync state
> support") was introduced in v5.10 and that seems to be the commit that
> broke suspend on Lazor.
> 

This isn't a response to your complete message but I'm going
to respond to this part.

Before runtime PM was in place, the "IPA clock" (which was a
logical notion representing the IPA core clock and all the
interconnects it uses) was enabled before the IPA hardware
was first touched.  It was disabled again when system suspend
occurred, and re-enabled again on system resume.  At one time
we did observe the XO clock turning off.

I'm not sure that answers your question.  But bottom line
is that system suspend/resume were supported (and made
IPA clock+interconnects get shut off and then on again),
but not runtime PM.

					-Alex