linux-kernel - Re: [PATCH v5 02/13] dt-bindings: remoteproc: qcom: pas: Add QMP property

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Date:   Fri, 20 Aug 2021 19:54:02 +0530
From:   Sibi Sankar <sibis@...eaurora.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     bjorn.andersson@...aro.org, mka@...omium.org, robh+dt@...nel.org,
        ulf.hansson@...aro.org, rjw@...ysocki.net, agross@...nel.org,
        ohad@...ery.com, mathieu.poirier@...aro.org,
        linux-arm-msm@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        dianders@...omium.org, rishabhb@...eaurora.org,
        sidgup@...eaurora.org
Subject: Re: [PATCH v5 02/13] dt-bindings: remoteproc: qcom: pas: Add QMP
 property

On 2021-08-20 00:25, Stephen Boyd wrote:
> Quoting Sibi Sankar (2021-08-18 20:02:05)
>> The load state power-domain, used by the co-processors to notify the
>> Always on Subsystem (AOSS) that a particular co-processor is up/down,
>> suffers from the side-effect of changing states during suspend/resume.
>> However the co-processors enter low-power modes independent to that of
>> the application processor and their states are expected to remain
>> unaltered across system suspend/resume cycles. To achieve this 
>> behavior
>> let's drop the load state power-domain and replace them with the qmp
>> property for all SoCs supporting low power mode signalling.
>> 
> 
> How do we drop the load state property without breaking existing DTBs?
> Maybe we need to leave it there and then somehow make it optional? Or 
> do
> we not care about this problem as the driver will start ignoring it?

We can afford to break the bindings
because of the following reason:

* Load state in mainline is currently
   broken i.e. it doesn't serve its
   main purpose of signalling AOP of
   the correct state of Q6 during
   system suspend/resume. Thus we
   can maintain current functionality
   even without the load state votes
   i.e. when a new kernel with load
   state removed is used with an older
   dtb the remoteproc functionality
   will remain the same.


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