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

[Ben Chuang]

Hi Stanisław,

On Wed, Aug 30, 2023 at 3:32 PM Stanisław Kardach <skardach@xxxxxxxxxx> wrote:
>
> On Wed, Aug 30, 2023 at 4:27 AM Ben Chuang <benchuanggli@xxxxxxxxx> wrote:
> >
> > Hi,
> > On Wed, Aug 30, 2023 at 12:35 AM Sven van Ashbrook <svenva@xxxxxxxxxxxx> wrote:
> > >
> > > + Rafael for advice on runtime_pm corner cases.
> > >
> > > On Mon, Aug 28, 2023 at 10:48 PM Ben Chuang <benchuanggli@xxxxxxxxx> 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?
> With runtime PM disabled via sysfs, the short answer is not since
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f9e5b33934cec24b8c024add5c5d65d2f93ade05.
>
> The longer answer is:
> 1. System boots up with LPM flags in PCI config space in default value
> (might be LPM enabled).
> 2.1. If runtime PM is disabled before first runtime suspend -
> registers will be left in their default state.
> 2.2. If runtime PM is disabled after first runtime suspend, the device
> will be woken up and the gl9763e runtime resume callback will disable
> LPM.

OK. Thank you for your answer.

Best Regards,
Ben Chuang

> >
> > >
> > > And the LPM negotiation flags look correct.
> > > Does that address your concerns?
> >
> > Best regards,
> > Ben Chuang
>
> --
> Best Regards,
> Stanisław Kardach