linux-kernel - Re: [PATCH 1/6] PM: runtime: enable wake irq after runtime

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Date:   Fri, 9 Apr 2021 13:14:40 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Chunfeng Yun <chunfeng.yun@...iatek.com>
Cc:     Tony Lindgren <tony@...mide.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" 
        <linux-usb@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC..." 
        <linux-mediatek@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Tianping Fang <tianping.fang@...iatek.com>,
        Eddie Hung <eddie.hung@...iatek.com>,
        Ikjoon Jang <ikjn@...omium.org>,
        Nicolas Boichat <drinkcat@...omium.org>
Subject: Re: [PATCH 1/6] PM: runtime: enable wake irq after runtime_suspend
 hook called

On Fri, Apr 9, 2021 at 10:36 AM Chunfeng Yun <chunfeng.yun@...iatek.com> wrote:
>
> On Fri, 2021-04-09 at 08:39 +0300, Tony Lindgren wrote:
> > * Chunfeng Yun <chunfeng.yun@...iatek.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@...iatek.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?