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

From: Charles Keepax <ckeepax@opensource.cirrus.com>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>,
	Lee Jones <lee.jones@linaro.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Cory Maccarrone <darkstar6262@gmail.com>,
	David Dajun Chen <dchen@diasemi.com>,
	Dong Aisheng <dong.aisheng@linaro.org>,
	Eric Miao <eric.miao@marvell.com>,
	Graeme Gregory <gg@slimlogic.co.uk>,
	Guennadi Liakhovetski <g.liakhovetski@gmx.de>,
	Haojian Zhuang <haojian.zhuang@marvell.com>,
	<jinyoungp@nvidia.com>,
	Jorge Eduardo Candelaria <jedu@slimlogic.co.uk>,
	Laxman Dewangan <ldewangan@nvidia.com>,
	Mark Brown <broonie@opensource.wolfsonmicro.com>,
	Mattias NILSSON <mattias.i.nilsson@stericsson.com>,
	Michael Hennerich <michael.hennerich@analog.com>,
	Mike Rapoport <mike@compulab.co.il>,
	ext Tony Lindgren <tony@atomide.com>,
	Venu Byravarasu <vbyravarasu@nvidia.com>,
	Linux-OMAP <linux-omap@vger.kernel.org>,
	<patches@opensource.cirrus.com>,
	Support Opensource <support.opensource@diasemi.com>
Subject: Re: [PATCH v2 00/22] mfd: demodularization of non-modular drivers
Date: Wed, 5 Dec 2018 13:40:16 +0000	[thread overview]
Message-ID: <20181205134016.GE16508@imbe.wolfsonmicro.main> (raw)
In-Reply-To: <CACRpkdZs0uSrsY66X67=h=BPy=P_5korWVM8kDbzTXrhrvKvcQ@mail.gmail.com>

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@opensource.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