linux-kernel - Re: [PATCH 2/2] mmc: sdhci-of-at91: set clocks and presets after resume from deepest PM

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Message-ID: <20170711143656.o4kkk6uwfghe6cyb@rfolt0960.corp.atmel.com>
Date:   Tue, 11 Jul 2017 16:36:56 +0200
From:   Ludovic Desroches <ludovic.desroches@...rochip.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
CC:     Quentin Schulz <quentin.schulz@...e-electrons.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        <nicolas.ferre@...rochip.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>
Subject: Re: [PATCH 2/2] mmc: sdhci-of-at91: set clocks and presets after
 resume from deepest PM

On Tue, Jul 11, 2017 at 03:54:17PM +0200, Ulf Hansson wrote:
> On 11 July 2017 at 15:33, Ludovic Desroches
> <ludovic.desroches@...rochip.com> wrote:
> > On Tue, Jul 11, 2017 at 02:42:44PM +0200, Ulf Hansson wrote:
> >> On 16 June 2017 at 09:29, Quentin Schulz
> >> <quentin.schulz@...e-electrons.com> wrote:
> >> > This adds deepest (Backup+Self-Refresh) PM support to the ATMEL SAMA5D2
> >> > SoC's SDHCI controller.
> >> >
> >> > When resuming from deepest state, it is required to restore preset
> >> > registers as the registers are lost since VDD core has been shut down
> >> > when entering deepest state on the SAMA5D2. The clocks need to be
> >> > reconfigured as well.
> >>
> >> Right, so compared to runtime resume there is some additional
> >> operations that is needed during system resume. Fair enough.
> >>
> >> However by looking at the changes below, you also change the system
> >> suspend operations, as it now calls sdhci_suspend_host(). Is that
> >> change needed? Then why?
> >>
> >> >
> >> > The other registers and init process are taken care of by the SDHCI
> >> > core.
> >> >
> >> > Signed-off-by: Quentin Schulz <quentin.schulz@...e-electrons.com>
> >> > ---
> >> >  drivers/mmc/host/sdhci-of-at91.c | 34 ++++++++++++++++++++++++++++++++--
> >> >  1 file changed, 32 insertions(+), 2 deletions(-)
> >> >
> >> > diff --git a/drivers/mmc/host/sdhci-of-at91.c b/drivers/mmc/host/sdhci-of-at91.c
> >> > index fb8c6011f13d..300513fc1068 100644
> >> > --- a/drivers/mmc/host/sdhci-of-at91.c
> >> > +++ b/drivers/mmc/host/sdhci-of-at91.c
> >> > @@ -207,6 +207,37 @@ static int sdhci_at91_set_clks_presets(struct device *dev)
> >> >  }
> >> >
> >> >  #ifdef CONFIG_PM
> >> > +static int sdhci_at91_suspend(struct device *dev)
> >> > +{
> >> > +       struct sdhci_host *host = dev_get_drvdata(dev);
> >> > +       struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
> >> > +       struct sdhci_at91_priv *priv = sdhci_pltfm_priv(pltfm_host);
> >> > +       int ret;
> >> > +
> >> > +       ret = sdhci_suspend_host(host);
> >> > +
> >>
> >> This is wrong, you can't call sdhci_suspend_host() unless the device
> >> is runtime resumed...
> >>
> >> > +       if (host->runtime_suspended)
> >> > +               return ret;
> >>
> >> ... and this is weird...
> >>
> >> > +
> >> > +       clk_disable_unprepare(priv->gck);
> >> > +       clk_disable_unprepare(priv->hclock);
> >> > +       clk_disable_unprepare(priv->mainck);
> >> > +
> >> > +       return ret;
> >> > +}
> >> > +
> >> > +static int sdhci_at91_resume(struct device *dev)
> >> > +{
> >> > +       struct sdhci_host *host = dev_get_drvdata(dev);
> >> > +       int ret;
> >> > +
> >> > +       ret = sdhci_at91_set_clks_presets(dev);
> >> > +       if (ret)
> >> > +               return ret;
> >>
> >> Instead of doing it like this, I suggest you set a new flag to true
> >> here, let's call it "restore_needed".
> >>
> >> In the ->runtime_resume() callback, you check the restore_needed flag
> >> and performs the extra operations in that case. When that's done, the
> >> ->runtime_resume() callback clears the flag, as to avoid the next
> >> runtime resume from unnecessary doing the extra operations.
> >>
> >> > +
> >> > +       return sdhci_resume_host(host);
> >>
> >> Remove this and call pm_runtime_force_resume().
> >>
> >> > +}
> >> > +
> >> >  static int sdhci_at91_runtime_suspend(struct device *dev)
> >> >  {
> >> >         struct sdhci_host *host = dev_get_drvdata(dev);
> >> > @@ -256,8 +287,7 @@ static int sdhci_at91_runtime_resume(struct device *dev)
> >> >  #endif /* CONFIG_PM */
> >> >
> >> >  static const struct dev_pm_ops sdhci_at91_dev_pm_ops = {
> >> > -       SET_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend,
> >>
> >> Leave the pm_runtime_force_suspend() here, unless you have other
> >> reasons not being described in the change log, to change the system
> >> suspend operations.
> >
> > I think we need to keep it to be able to set the restore_needed flag, isn't it?
> 
> Yeah, perhaps it's better to set the flag from sdhci_at91_suspend()
> and instead leave the resume callback being assigned to
> pm_runtime_force_resume().
> 
> I guess that is what you meant?

Exactly. Thanks for your smart solution!

Regards

Ludovic