Date:   Thu, 20 Aug 2020 12:39:07 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Frank Wunderlich <wichtig@...web.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Collabora Kernel ML <kernel@...labora.com>,
        Frank Wunderlich <linux@...web.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Hanks Chen <hanks.chen@...iatek.com>,
        Jason Cooper <jason@...edaemon.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH] Revert "irqchip/mtk-sysirq: Convert to a platform driver"

On Thu, Aug 20, 2020 at 7:53 AM Marc Zyngier <maz@...nel.org> wrote:
>
> On 2020-08-20 09:07, Saravana Kannan wrote:
> > On Thu, Aug 20, 2020 at 12:56 AM Marc Zyngier <maz@...nel.org> wrote:
> >>
> >> On 2020-08-19 19:51, Saravana Kannan wrote:
> >> > On Wed, Aug 19, 2020 at 9:52 AM Frank Wunderlich <wichtig@...web.de>
> >> > wrote:
> >> >>
> >> >> hi,
> >> >>
> >> >> does the fix you've linked to my revert [1] not work in your case?
> >> >>
> >> >> [1] https://patchwork.kernel.org/patch/11718481/
> >> >
> >> > Thanks for pointing it out Frank. Also, might want to avoid top
> >> > posting in the future.
> >> >
> >> > Enric, Can you please try that other fix and see if that solves your
> >> > issue?
> >>
> >> I think Enric was clear that the driver does probe correctly
> >> (meaning that he has the fix in his tree). It is everything else
> >> that breaks, because none of the drivers on the platform are
> >> equipped to defer their own probing.
> >>
> >> I think we need to change this works right now, meaning that we can't
> >> blindly change the behaviour of *built-in* drivers. I'll see if I can
> >> come up with something quickly, but I'll otherwise take Enric patch.
> >
> > Sounds fair Marc.
> >
> > Btw, Enric, out of curiosity, can you try adding "fw_devlink=on" to
> > your kernel command line to see if it helps? It basically ensures
> > proper probe ordering without depending on the drivers. There are some
> > corner cases where it still can't work properly (too much to explain
> > for a late night email), but if the platforms don't have those corner
> > cases it'll work perfectly.
> >
> > I'm fine with the revert if Marc isn't able to find a quick fix to the
> > drivers, but this might also fix your problem right away.
>
> I'm afraid there is no quick fix if we want to preserve the current
> behavior with built-in drivers,

> and not having "fw_devlink=on" by
> default makes it irrelevant for most people.

Agreed.

> fw_devlink also prevents my test platforms from booting (my rk3399
> doesn't find its PCI devices with it), while the same kernel boots
> just fine without it. It could well be that the corner case is
> likely to be more prevalent than you seem to expect.

Yeah, I know it has a few corner cases I need to deal with.

> I will probably end-up end-up queuing reverts for both mtk-sysirq,
> mtk-cirq, and qcom-pdc (the first two can't be built as module with
> mainline anyway, and I seem to remember that the latter caused some
> controversy as well).
>
> As an experiment, I have pushed out a branch[1] that implements
> a "hybrid" probe, retaining the previous early probe mechanism when
> the driver is built-in, and letting things rip when built as a
> module (if you do that, you hopefully know what you are doing).
> I'd welcome some testing on affected platforms (I don't have
> anything I can run mainline on that'd be affected).

I like [1] and the code looks good. Hopefully, we can stick with that.

-Saravana

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