linux-kernel - Re: [PATCH v2 00/22] mfd: demodularization of non-modular drivers

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Date:   Wed, 5 Dec 2018 13:40:16 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Linus Walleij <linus.walleij@...aro.org>
CC:     Paul Gortmaker <paul.gortmaker@...driver.com>,
        Lee Jones <lee.jones@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Cory Maccarrone <darkstar6262@...il.com>,
        David Dajun Chen <dchen@...semi.com>,
        Dong Aisheng <dong.aisheng@...aro.org>,
        Eric Miao <eric.miao@...vell.com>,
        Graeme Gregory <gg@...mlogic.co.uk>,
        Guennadi Liakhovetski <g.liakhovetski@....de>,
        Haojian Zhuang <haojian.zhuang@...vell.com>,
        <jinyoungp@...dia.com>,
        Jorge Eduardo Candelaria <jedu@...mlogic.co.uk>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Mark Brown <broonie@...nsource.wolfsonmicro.com>,
        Mattias NILSSON <mattias.i.nilsson@...ricsson.com>,
        Michael Hennerich <michael.hennerich@...log.com>,
        Mike Rapoport <mike@...pulab.co.il>,
        ext Tony Lindgren <tony@...mide.com>,
        Venu Byravarasu <vbyravarasu@...dia.com>,
        Linux-OMAP <linux-omap@...r.kernel.org>,
        <patches@...nsource.cirrus.com>,
        Support Opensource <support.opensource@...semi.com>
Subject: Re: [PATCH v2 00/22] mfd: demodularization of non-modular drivers

On Wed, Dec 05, 2018 at 12:48:47PM +0100, Linus Walleij wrote:
> On Wed, Dec 5, 2018 at 12:36 PM Charles Keepax
> <ckeepax@...nsource.cirrus.com> wrote:
> > On Sun, Dec 02, 2018 at 11:23:07PM -0500, Paul Gortmaker wrote:
> > > The solution to #4 is similar - we delete the ".remove" function and
> > > the binding into the platform_driver struct.  However, since the same
> > > ".remove" function could also be triggered by an "unbind" (such as for
> > > pass-through of a device to a guest instance)  - so we also explicitly
> > > disable any unbind for the driver.
> > >
> > > The unbind mask allows us to ensure we will see if there was some odd
> > > corner case out there that was relying on it.  Typically it would be a
> > > multi-port ethernet card passing a port through to a guest, so a
> > > sensible use case in MFD drivers seems highly unlikely.  This same
> > > solution has already been used in multiple other mainline subsystems.
> > >
> >
> > I guess if this is a general direction thing, but it does seem
> > that module unload is not the only reason one might ever unbind a
> > driver. So are we sure we want to remove the option to unbind
> > these drivers? Certainly for testing it is sometimes useful.
> 
> I personally never understood why these attributes are even
> present on non-modular drivers.
> 
> If testing is about exercising unbind/bind to reintialize
> the code through a new call to .probe(), why would the developer
> not take it all the way through and make it a module?
> It just looks like a half-measure.
> 

Well I guess in someways it is a half-measure. I vaguely seem to
remember some dependency nightmare that can make it really hard
to have the MFD allowed as a module in some cases, I can't
remember the exact details but probably why some of these are not
modules.

I certainly don't strongly object to removing the ability to
unbind these drivers, just wanted to make sure everyone is
aligned that it's a good thing to do. Does kinda remove a couple
of debugging options (debugging things like drivers interfering
with each other) and the last chance restart the driver and see
if that helps rescue something.

Thanks,
Charles