linux-kernel - Re: [PATCH V4] mmc: sdhci-msm: Update system suspend/resume callbacks of sdhci-msm platform driver

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Date:   Mon, 20 Apr 2020 11:29:06 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Shaik Sajida Bhanu <sbhanu@...eaurora.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Asutosh Das <asutoshd@...eaurora.org>,
        Sahitya Tummala <stummala@...eaurora.org>,
        Sayali Lokhande <sayalil@...eaurora.org>, cang@...eaurora.org,
        Veerabhadrarao Badiganti <vbadigan@...eaurora.org>,
        Ram Prakash Gupta <rampraka@...eaurora.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCH V4] mmc: sdhci-msm: Update system suspend/resume callbacks
 of sdhci-msm platform driver

On Wed, 15 Apr 2020 at 01:16, Stephen Boyd <swboyd@...omium.org> wrote:
>
> Quoting Ulf Hansson (2020-03-20 03:22:01)
> > On Thu, 19 Mar 2020 at 18:42, Stephen Boyd <swboyd@...omium.org> wrote:
> > >
> > > Quoting Ulf Hansson (2020-03-06 02:07:41)
> > > > On Wed, 4 Mar 2020 at 17:46, Stephen Boyd <swboyd@...omium.org> wrote:
> > > > >
> > > > > Quoting Ulf Hansson (2020-03-04 07:34:29)
> > > > > > On Thu, 20 Feb 2020 at 07:45, Shaik Sajida Bhanu <sbhanu@...eaurora.org> wrote:
> > > > > > >
> > > > > > > The existing suspend/resume callbacks of sdhci-msm driver are just
> > > > > > > gating/un-gating the clocks. During suspend cycle more can be done
> > > > > > > like disabling controller, disabling card detection, enabling wake-up events.
> > > > > > >
> > > > > > > So updating the system pm callbacks for performing these extra
> > > > > > > actions besides controlling the clocks.
> > > > > > >
> > > > > > > Signed-off-by: Shaik Sajida Bhanu <sbhanu@...eaurora.org>
> > > > > > > Reviewed-by: Stephen Boyd <swboyd@...omium.org>
> > > > > > > ---
> > > [...]
> > > >
> > > > >
> > > > > >
> > > > > > > +
> > > > > > > +       ret = pm_runtime_force_suspend(dev);
> > > > > >
> > > > > > It looks to me that perhaps you could make use of solely
> > > > > > pm_runtime_force_suspend(), then just skip calling
> > > > > > sdhci_suspend|resume_host() altogether. Do you think that could work?
> > > > >
> > > > > Does that do all the things the commit text mentions is desired for
> > > > > system suspend?
> > > >
> > > > No. :-)
> > > >
> > > > But why is system wakeup needed for an eMMC card?
> > > >
> > >
> > > I don't know if system wakeup is needed for an eMMC card. Probably only
> > > if you plug in a card and some daemon wants to wake up and probe the
> > > card for auto-play or something like that? Seems possible so might as
> > > well expose the CD gpio as a wakeup in that case and let userspace
> > > decide if it wants to do that.
> >
> > Right, card detect IRQs could be useful for system wakeups.
> >
> > I assume you are using a GPIO IRQ for that, which is easily managed,
> > as the runtime PM status of the mmc controller is irrelevant when
> > configuring the GPIO IRQ as wakeup.
> >
> > We even have a helper for doing this, mmc_gpio_set_cd_wake().
>
> Right. Maybe mmc_gpio_set_cd_wake() needs to be called from somewhere in
> the sdhci core?

Yes, that seems reasonable.

>
> >
> > >
> > > Is runtime suspended state the same as system suspended state here
> > > though? The commit text seems to imply that only clks are disabled when
> > > it's desirable to disable the entire controller. I'm still fuzzy on how
> > > runtime PM and system PM interact because it seems to have changed since
> > > I looked last a few years ago. If the driver can stay in a runtime
> > > suspended state across system suspend then I'm all for it. That would
> > > save time for system PM transitions.
> >
> > In most cases this should be possible. And so far, for this case, I
> > haven't found a good reason to why it shouldn't work.
> >
> > Although, perhaps we need to improve some of the sdhci's library
> > functions for PM, to better support this.
> >
>
> So does that mean it's all just working then? Nothing to do here except
> make wakeup irqs for CD work?

Well, if it "works " or not, I am not really sure.

My point is, I think most of the things that need to be managed at
system suspend/resume are the same things that need to be managed
during runtime suspend/resume (except wakeups). So, rather than
implementing a whole bunch of system suspend/resume specific things,
why not make use of the runtime suspend/resume callbacks instead.

Kind regards
Uffe