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

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Date:   Sat, 10 Apr 2021 09:44:21 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
CC:     Tony Lindgren <tony@...mide.com>, 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, 2021-04-09 at 13:14 +0200, Rafael J. Wysocki wrote:
> 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.
Got it
> 
> I'm not sure if I understand the underlying problem correctly.  Is it
> about addressing spurious wakeups?
In fact, it's default value is the same as the wakeup signal, maybe the
above case, using level trigger, should be avoided, it is not clear and
causes confusion, as Ikjoon and Tony suggested, using falling edge type
is better.

Thanks a lot