linux-kernel - Re: [PATCH v2 1/2] PM / Domains: Add GENPD_FLAG_NO

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Date:   Fri, 21 Aug 2020 14:41:28 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Sibi Sankar <sibis@...eaurora.org>, bjorn.andersson@...aro.org,
        khilman@...nel.org, ulf.hansson@...aro.org
Cc:     rjw@...ysocki.net, agross@...nel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        gregkh@...uxfoundation.org, pavel@....cz, len.brown@...el.com,
        rnayak@...eaurora.org, dianders@...omium.org, mka@...omium.org,
        Sibi Sankar <sibis@...eaurora.org>
Subject: Re: [PATCH v2 1/2] PM / Domains: Add GENPD_FLAG_NO_SUSPEND/RESUME flags

Quoting Sibi Sankar (2020-08-21 13:49:20)
> Add GENPD_FLAG_NO_SUSPEND/RESUME flags to instruct genpd to keep the
> status of the PM domain unaltered during suspend/resume respectively.
> The flags are aimed at power domains coupled to co-processors which
> enter low-power modes independent to that of the application processor.
> 
> Specifically the flags are to be used by the power domains exposed
> by the AOSS QMP driver linked to modem, adsp, cdsp remoteprocs. These
> power domains are used to notify the Always on Subsystem (AOSS) that
> a particular co-processor is up. AOSS uses this information to wait
> for the co-processors to suspend before starting its sleep sequence.
> The application processor powers off these power domains only if the
> co-processor has crashed or powered off and remains unaltered during
> system suspend/resume.

Why are these power domains instead of some QMP message sent during
remote proc power up? If this has been discussed before feel free to
disregard and please link to prior mailing list discussions.

I find it odd that this is modeled as a power domain instead of some
Qualcomm specific message that the remoteproc driver sends to AOSS. Is
there some sort of benefit the driver gets from using the power domain
APIs for this vs. using a custom API?