linux-kernel - Re: [PATCH 0/6] irqchip: Hybrid probing

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Date:   Wed, 16 Sep 2020 09:51:13 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Rob Herring <robh@...nel.org>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Frank Wunderlich <linux@...web.de>,
        John Stultz <john.stultz@...aro.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Hanks Chen <hanks.chen@...iatek.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Frank Rowand <frowand.list@...il.com>, kernel-team@...roid.com
Subject: Re: [PATCH 0/6] irqchip: Hybrid probing

On 2020-09-15 22:13, Rob Herring wrote:
> On Sat, Sep 12, 2020 at 01:51:42PM +0100, Marc Zyngier wrote:
>> A recent attempt at converting a couple of interrupt controllers from
>> early probing to standard platform drivers have badly failed, as it
>> became evident that although an interrupt controller can easily probe
>> late, device drivers for the endpoints connected to it are rarely
>> equipped to deal with probe deferral. Changes were swiftly reverted.
>> 
>> However, there is some value in *optionally* enabling this, if only
>> for development purposes, as there is otherwise a "chicken and egg"
>> problem, and a few people (cc'd) are working on a potential solution.
>> 
>> This short series enables the infrastructure for modular building
>> whilst retaining the usual early probing for monolithic build, and
>> introduces it to the three drivers that were previously made to probe
>> as platform drivers.
> 
> I hardly expected more OF_DECLARE macros when I opened this up. Given
> desires to get rid of them, I don't think adding to it is the way
> forward. That wrapping a platform driver around OF_DECLARE looks pretty
> horrible IMO.

Nobody said it was cute. It's a band aid that allows us to move from the
status-quo that exists today. How would you propose we allow people to
go and start "fixing" drivers if you don't give them the opportunity
to even start trying?

> I browsed some of the discussion around this. It didn't seem like it's
> a large number of drivers that have to be fixed to defer probe
> correctly. Am I missing something?

Well, that was enough drivers for the two platforms that had it enabled
to break horribly, without a way to go back to a working state. Do you
find that acceptable? I don't.

> I'd rather keep the pressure on getting fw_devlink on by default.

So far, fw_devlink breaks everything under the sun, even without modular
irqchips. Most of my systems fail to boot if I enable it. So yes, it
really needs some work. And this series allows this work to happen.

         M.
-- 
Jazz is not dead. It just smells funny...