linux-kernel - Re: [PATCH] misc: rtsx: rts5249 support runtime PM

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Date:   Thu, 26 Nov 2020 16:02:05 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        吳昊澄 Ricky <ricky_wu@...ltek.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "vaibhavgupta40@...il.com" <vaibhavgupta40@...il.com>,
        "kdlnx@...h.eu" <kdlnx@...h.eu>,
        Doug Anderson <dianders@...omium.org>,
        "rmfrfs@...il.com" <rmfrfs@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] misc: rtsx: rts5249 support runtime PM

On Thu, 26 Nov 2020 at 15:19, Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Nov 26, 2020 at 4:07 AM 吳昊澄 Ricky <ricky_wu@...ltek.com> wrote:
> >
> > > -----Original Message-----
> > > From: Rafael J. Wysocki [mailto:rafael@...nel.org]
> > > Sent: Wednesday, November 25, 2020 10:04 PM
> > > To: Bjorn Helgaas; 吳昊澄 Ricky
>
> [cut]
>
> > > > > +static void rtsx_pci_rtd3_work(struct work_struct *work)
> > > > > +{
> > > > > +     struct delayed_work *dwork = to_delayed_work(work);
> > > > > +     struct rtsx_pcr *pcr = container_of(dwork, struct rtsx_pcr,
> > > rtd3_work);
> > > > > +
> > > > > +     pcr_dbg(pcr, "--> %s\n", __func__);
> > > > > +
> > > > > +     while (pcr->pci->dev.power.usage_count.counter > 0) {
> > > > > +             if (pm_runtime_active(&(pcr->pci->dev)))
> > > > > +                     pm_runtime_put(&(pcr->pci->dev));
> > > >
> > > > I'm not a runtime PM expert, but this looks fishy.  AFAICT this is the
> > > > only driver in the tree that uses usage_count.counter this way, which
> > > > is a pretty big hint that this needs a closer look.  Cc'd Rafael.
> > >
> > > You are right, this is not correct from the PM-runtime POV.
> > >
> > > It looks like this attempts to force the PM-runtime usage counter down
> > > to 0 and it's kind of hard to say why this is done (and it shouldn't
> > > be done in the first place, because it destroys the usage counter
> > > balance).
> > >
> > > Ricky, is this an attempt to work around an issue of some sort?
> > >
> >
> > Thanks Bjorn and Rafael
> > I found when we boot up, our dev pcr->pci->dev.power.usage_count.counter always is 2,
> > Don’t know how to make it to 0 because we need to support D3 and run runtime_suspended callback function
> > Is there something wrong with us to enable runtime PM?
>
> That is possible.
>
> If you want it to be enabled by default, you need to call
> pm_runtime_allow() from the driver at probe time, in addition to
> pm_runtime_enable(), in the first place, but that only drops one
> reference, so question is where the other one comes from.

Yes, good point.

Moreover, I am wondering whether you also need to deploy support for
runtime PM for the child device (managed by
drivers/mmc/host/rtsx_pci_sdmmc.c driver), as to make the support
complete.

>
> Are the pm_runtime_get*() and pm_runtime_put*() calls balanced?

Perhaps have a look at how the drivers/misc/cardreader/rtsx_usb.c and
drivers/mmc/host/rtsx_usb_sdmmc.c have implemented this could help. I
know it's USB, but it should work quite similar in regards to runtime
PM, I think.

Kind regards
Uffe