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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Fri, 9 Apr 2021 13:14:40 +0200
Message-ID: <CAJZ5v0ioobLt5aEm8TAcPKgJiL13OJ7KqTeJmcQCuVp8ALxBmw@mail.gmail.com>
Subject: Re: [PATCH 1/6] PM: runtime: enable wake irq after runtime_suspend
 hook called
To:     Chunfeng Yun <chunfeng.yun@mediatek.com>
Cc:     Tony Lindgren <tony@atomide.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mathias Nyman <mathias.nyman@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
        "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" 
        <linux-usb@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
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        <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Tianping Fang <tianping.fang@mediatek.com>,
        Eddie Hung <eddie.hung@mediatek.com>,
        Ikjoon Jang <ikjn@chromium.org>,
        Nicolas Boichat <drinkcat@chromium.org>
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On Fri, Apr 9, 2021 at 10:36 AM Chunfeng Yun <chunfeng.yun@mediatek.com> wrote:
>
> On Fri, 2021-04-09 at 08:39 +0300, Tony Lindgren wrote:
> > * Chunfeng Yun <chunfeng.yun@mediatek.com> [210409 01:54]:
> > > On Thu, 2021-04-08 at 19:41 +0200, Rafael J. Wysocki wrote:
> > > > On Thu, Apr 8, 2021 at 11:35 AM Chunfeng Yun <chunfeng.yun@mediatek.com> wrote:
> > > > >
> > > > > When the dedicated wake irq is level trigger, enable it before
> > > > > calling runtime_suspend, will trigger an interrupt.
> > > > >
> > > > > e.g.
> > > > > for a low level trigger type, it's low level at running time (0),
> > > > > and becomes high level when enters suspend (runtime_suspend (1) is
> > > > > called), a wakeup signal at (2) make it become low level, wake irq
> > > > > will be triggered.
> > > > >
> > > > >                 ------------------
> > > > >                |           ^     ^|
> > > > > ----------------           |     | --------------
> > > > >  |<---(0)--->|<--(1)--|   (3)   (2)    (4)
> > > > >
> > > > > if we enable the wake irq before calling runtime_suspend during (0),
> > > > > an interrupt will arise, it causes resume immediately;
> > > >
> > > > But that's necessary to avoid missing a wakeup interrupt, isn't it?
> > > That's also what I worry about.
> >
> > Yeah sounds like this patch will lead into missed wakeirqs.
> If miss level trigger wakeirqs, that means HW doesn't latch it? is it HW
> limitation?

If it's level-triggered, it won't be missed, but then it is just
pointless to suspend the device when wakeup is being signaled in the
first place.

I'm not sure if I understand the underlying problem correctly.  Is it
about addressing spurious wakeups?