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

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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



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