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

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Message-ID: <CACT4zj_84eCYOq56zdqaydaEGqyqBrXDrsTkDRyCntvVF78-0A@mail.gmail.com>
Date:   Wed, 30 Aug 2023 10:26:42 +0800
From:   Ben Chuang <benchuanggli@...il.com>
To:     Sven van Ashbrook <svenva@...omium.org>
Cc:     "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        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

Hi,
On Wed, Aug 30, 2023 at 12:35 AM Sven van Ashbrook <svenva@...omium.org> wrote:
>
> + 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.
This is ok.

>
> - "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.
In this cas, after gl9763e_resume(), it is LPM disabled.
Is there no chance for gl9763e to enter L1.x again when the system is idle?

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

Best regards,
Ben Chuang