linux-kernel - Re: [PATCH v2] mmc: sdhci-pci-gli: fix LPM negotiation so x86/S0ix SoCs can suspend

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Date:   Tue, 29 Aug 2023 12:35:07 -0400
From:   Sven van Ashbrook <svenva@...omium.org>
To:     Ben Chuang <benchuanggli@...il.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Cc:     skardach@...gle.com, adrian.hunter@...el.com,
        SeanHY.chen@...esyslogic.com.tw, ben.chuang@...esyslogic.com.tw,
        greg.tu@...esyslogic.com.tw, jason.lai@...esyslogic.com.tw,
        jasonlai.genesyslogic@...il.com, linux-kernel@...r.kernel.org,
        linux-mmc@...r.kernel.org, reniuschengl@...il.com,
        stable@...r.kernel.org, ulf.hansson@...aro.org,
        victor.shih@...esyslogic.com.tw, victorshihgli@...il.com
Subject: Re: [PATCH v2] mmc: sdhci-pci-gli: fix LPM negotiation so x86/S0ix
 SoCs can suspend

+ Rafael for advice on runtime_pm corner cases.

On Mon, Aug 28, 2023 at 10:48 PM Ben Chuang <benchuanggli@...il.com> wrote:
>
>
> My concern is that when runtime_pm is false, gl9763e is disabled LPM
> negotiation, gl9763e can't enter L1.x and s0ix may fail.
> It seems that runtime_pm will always exist and that's ok.
>

Thank you. I believe we can address your concern.

- XXX_suspend/XXX_resume (i.e. classic suspend/resume) depends on
  CONFIG_PM_SLEEP. This always selects CONFIG_PM. This always includes
  the runtime_pm framework. So, if XXX_suspend/XXX_resume gets called,
  the runtime_pm framework is always present, but may not be actively
  managing the device.

- "when runtime_pm is false" AFAIK the only way to disable runtime_pm
  when CONFIG_PM is set, is to write "on" to /sys/devices/.../power/control.
  See https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-devices-power
  In that case, the runtime_pm framework will activate the device, calling
  XXX_runtime_resume() if necessary. Are there other ways of disabling it?

- if /sys/devices/.../power/control is "on", then:
  gl9763e_runtime_resume() always called -> LPM always disabled
  gl9763e_suspend() -> LPM enabled -> gl9763e_resume() -> LPM disabled
  In between "classic" XXX_suspend and XXX_resume, LPM will be enabled,
  so the device can enter L1.x and S0ix.

And the LPM negotiation flags look correct.
Does that address your concerns?