linux-kernel - Re: [PATCH 0/4] mwifiex PCI/wake-up interrupt fixes

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Message-ID: <20190227205754.GF174696@google.com>
Date:   Wed, 27 Feb 2019 12:57:55 -0800
From:   Brian Norris <briannorris@...omium.org>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Ganapathi Bhat <gbhat@...vell.com>,
        Jeffy Chen <jeffy.chen@...k-chips.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Devicetree List <devicetree@...r.kernel.org>,
        Xinming Hu <huxinming820@...il.com>,
        "<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
        linux-pm <linux-pm@...r.kernel.org>,
        "<linux-wireless@...r.kernel.org>" <linux-wireless@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Amitkumar Karwar <amitkarwar@...il.com>,
        linux-rockchip@...ts.infradead.org,
        Nishant Sarmukadam <nishants@...vell.com>,
        Rob Herring <robh+dt@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Kalle Valo <kvalo@...eaurora.org>,
        Tony Lindgren <tony@...mide.com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 0/4] mwifiex PCI/wake-up interrupt fixes

Hi Ard,

On Wed, Feb 27, 2019 at 11:16:12AM +0100, Ard Biesheuvel wrote:
> On Wed, 27 Feb 2019 at 11:02, Marc Zyngier <marc.zyngier@....com> wrote:
> > On 26/02/2019 23:28, Brian Norris wrote:
> > > You're not the first person to notice this. All the motivations are not
> > > necessarily painted clearly in their cover letter, but here are some
> > > previous attempts at solving this problem:
> > >
> > > [RFC PATCH v11 0/5] PCI: rockchip: Move PCIe WAKE# handling into pci core
> > > https://lkml.kernel.org/lkml/20171225114742.18920-1-jeffy.chen@rock-chips.com/
> > > http://lkml.kernel.org/lkml/20171226023646.17722-1-jeffy.chen@rock-chips.com/
> > >
> > > As you can see by the 12th iteration, it wasn't left unsolved for lack
> > > of trying...
> >
> > I wasn't aware of this. That's definitely a better approach than my
> > hack, and I would really like this to be revived.
> >
> 
> I don't think this approach is entirely sound either.

(I'm sure there may be problems with the above series. We probably
should give it another shot though someday, as I think it's closer to
the mark.)

> From the side of the PCI device, WAKE# is just a GPIO line, and how it
> is wired into the system is an entirely separate matter. So I don't
> think it is justified to overload the notion of legacy interrupts with
> some other pin that may behave in a way that is vaguely similar to how
> a true wake-up capable interrupt works.

I think you've conflated INTx with WAKE# just a bit (and to be fair,
that's exactly what the bad binding we're trying to replace did,
accidentally). We're not trying to claim this WAKE# signal replaces the
typical PCI interrupts, but it *is* an interrupt in some sense --
"depending on your definition of interrupt", per our IRC conversation ;)

> So I'd argue that we should add an optional 'wake-gpio' DT property
> instead to the generic PCI device binding, and leave the interrupt
> binding and discovery alone.

So I think Mark Rutland already shot that one down; it's conceptually an
interrupt from the device's perspective. We just need to figure out a
good way of representing it that doesn't stomp on the existing INTx
definitions.

Brian