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Date:   Wed, 5 Dec 2018 13:08:43 -0500
From:   Paul Gortmaker <paul.gortmaker@windriver.com>
To:     Steve Twiss <stwiss.opensource@diasemi.com>
CC:     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 <david.chen@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>,
        Jin Park <jinyoungp@nvidia.com>,
        Jorge Eduardo Candelaria <jedu@slimlogic.co.uk>,
        Laxman Dewangan <ldewangan@nvidia.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        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>,
        Tony Lindgren <tony@atomide.com>,
        Venu Byravarasu <vbyravarasu@nvidia.com>,
        "linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>,
        "patches@opensource.cirrus.com" <patches@opensource.cirrus.com>,
        Support Opensource <Support.Opensource@diasemi.com>
Subject: Re: [PATCH v2 00/22] mfd: demodularization of non-modular drivers
Message-ID: <20181205180843.GD23156@windriver.com>
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[RE: [PATCH v2 00/22] mfd: demodularization of non-modular drivers] On 05/12/2018 (Wed 12:01) Steve Twiss wrote:

> Hi Paul,
> 
> On 03 December 2018 04:23, Paul Gortmaker wrote:
> 
> > Subject: [PATCH v2 00/22] mfd: demodularization of non-modular drivers
> > 
> > [v1 --> v2: add some more commits as requested by Lee (MFD maintainer),
> >  update the 00/NN text; re-do build and link testing on new linux-next. ]
> > 
> > This group of MFD drivers are all controlled by "bool" Kconfig settings,
> > but contain various amounts of largely pointless uses of infrastructure
> > related to modular operations, even though they can't be built modular.
> > 
> > We can easily remove/replace all of it.  We are trying to make driver
> > code consistent with the Makefiles/Kconfigs that control them. 
> 
> For the DA9052 and DA9055, changes:
> 
> -  drivers/mfd/da9052-core.c         | 11 -----------
> -  drivers/mfd/da9052-i2c.c          | 22 ++-------------------
> -  drivers/mfd/da9052-irq.c          |  1 -
> -  drivers/mfd/da9052-spi.c          | 22 ++-------------------
> -  drivers/mfd/da9055-core.c         | 13 ++-----------
> -  drivers/mfd/da9055-i2c.c          | 24 ++---------------------
> 
> The responsibility can fall back to Dialog for these changes. We will
> submit Kconfig patches for these and make them explicitly non-modular.
> This will remove the ambiguity caused by the Kconfig bool options.

[typo noted: non-modular ---> modular]

Great, I'll look forward to seeing those patches to convert  these
drivers to modular in the near future, and I'll not re-send mine.

Thanks,
P.
--


> 
> Regards,
> Steve
> 
> > This
> > means not using modular functions/macros for drivers that can never be
> > built as a module.  Some of the downfalls this oversight leads to are:
> > 
> >  (1) it is easy to accidentally write unused module_exit and remove code
> >  (2) it can be misleading when reading the source, thinking it can be
> >      modular when the Makefile and/or Kconfig prohibit it
> >  (3) it requires the include of the module.h header file which in turn
> >      includes nearly everything else, thus adding a lot of CPP overhead.
> >  (4) it gets copied/replicated into other drivers and spreads quickly.
> > 
> > What we see in current drivers falls into one or more of the following
> > categories:
> > 
> > 1) include of <linux/module.h> when it simply isn't needed
> > 
> > 2) Use of MODULE_LICENSE, MODULE_DEVICE_TABLE,  MODULE_AUTHOR etc.
> >    macros that are no-ops for non-modular drivers.
> > 
> > 3) Creation of a module_exit() function that will be compiled and
> >    linked in but never actually called for non-modular drivers.
> > 
> > 4) Addition of a platform_driver ".remove" function that is bound
> >    into the struct but will never be called for non-module use cases.
> > 
> > Solution to #1 --> #3 is simple ; we just delete the related code.
> > 
> > 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.
> > 
> > Build testing was done on drivers/mfd for allyesconfig on x86_64, ARM
> > and ARM-64 on a recent linux-next checkout.
> > 
> > Paul.
> > 
> > ---
> > 
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Cory Maccarrone <darkstar6262@gmail.com>
> > Cc: David Dajun Chen <dchen@diasemi.com>
> > Cc: Dong Aisheng <dong.aisheng@linaro.org>
> > Cc: Eric Miao <eric.miao@marvell.com>
> > Cc: Graeme Gregory <gg@slimlogic.co.uk>
> > Cc: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> > Cc: Haojian Zhuang <haojian.zhuang@marvell.com>
> > Cc: Jin Park <jinyoungp@nvidia.com>
> > Cc: Jorge Eduardo Candelaria <jedu@slimlogic.co.uk>
> > Cc: Laxman Dewangan <ldewangan@nvidia.com>
> > Cc: Lee Jones <lee.jones@linaro.org>
> > Cc: Linus Walleij <linus.walleij@linaro.org>
> > Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
> > Cc: Mattias Nilsson <mattias.i.nilsson@stericsson.com>
> > Cc: Michael Hennerich <michael.hennerich@analog.com>
> > Cc: Mike Rapoport <mike@compulab.co.il>
> > Cc: Tony Lindgren <tony@atomide.com>
> > Cc: Venu Byravarasu <vbyravarasu@nvidia.com>
> > Cc: linux-omap@vger.kernel.org
> > Cc: patches@opensource.cirrus.com
> > Cc: Support Opensource <support.opensource@diasemi.com>
> > 
> > 
> > Paul Gortmaker (22):
> >   mfd: aat2870-core: Make it explicitly non-modular
> >   mfd: adp5520: Make it explicitly non-modular
> >   mfd: as3711: Make it explicitly non-modular
> >   mfd: da903x: Make it explicitly non-modular
> >   mfd: da9052-*: Make it explicitly non-modular
> >   mfd: da9055-i2c: Make it explicitly non-modular
> >   mfd: da9055-core: make it explicitly non-modular
> >   mfd: db8500-prcmu: drop unused MODULE_ tags from non-modular code
> >   mfd: htc-i2cpld: Make it explicitly non-modular
> >   mfd: max8925-core: drop unused MODULE_ tags from non-modular code
> >   mfd: rc5t583: Make it explicitly non-modular
> >   mfd: sta2x11: drop unused MODULE_ tags from non-modular code
> >   mfd: syscon: Make it explicitly non-modular
> >   mfd: tps65090: Make it explicitly non-modular
> >   mfd: tps65910: Make it explicitly non-modular
> >   mfd: tps80031: Make it explicitly non-modular
> >   mfd: wm831x-spi: Make it explicitly non-modular
> >   mfd: wm831x-i2c: Make it explicitly non-modular
> >   mfd: wm831x-core: drop unused MODULE_ tags from non-modular code
> >   mfd: wm8350-i2c: Make it explicitly non-modular
> >   mfd: wm8350-core: drop unused MODULE_ tags from non-modular code
> >   mfd: wm8400-core: Make it explicitly non-modular
> > 
> >  drivers/mfd/aat2870-core.c        | 40 +++------------------------------------
> >  drivers/mfd/adp5520.c             | 30 +++++++----------------------
> >  drivers/mfd/as3711.c              | 14 --------------
> >  drivers/mfd/da903x.c              | 26 +++----------------------
> >  drivers/mfd/da9052-core.c         | 11 -----------
> >  drivers/mfd/da9052-i2c.c          | 22 ++-------------------
> >  drivers/mfd/da9052-irq.c          |  1 -
> >  drivers/mfd/da9052-spi.c          | 22 ++-------------------
> >  drivers/mfd/da9055-core.c         | 13 ++-----------
> >  drivers/mfd/da9055-i2c.c          | 24 ++---------------------
> >  drivers/mfd/db8500-prcmu.c        | 10 ++++------
> >  drivers/mfd/htc-i2cpld.c          | 18 +-----------------
> >  drivers/mfd/max8925-core.c        |  7 +------
> >  drivers/mfd/rc5t583.c             | 14 --------------
> >  drivers/mfd/sta2x11-mfd.c         | 10 ++++------
> >  drivers/mfd/syscon.c              | 12 +-----------
> >  drivers/mfd/tps65090.c            | 30 +++++------------------------
> >  drivers/mfd/tps65910.c            | 18 +-----------------
> >  drivers/mfd/tps80031.c            | 37 ++----------------------------------
> >  drivers/mfd/wm831x-core.c         |  7 ++-----
> >  drivers/mfd/wm831x-i2c.c          | 20 ++------------------
> >  drivers/mfd/wm831x-spi.c          | 24 ++---------------------
> >  drivers/mfd/wm8350-core.c         |  6 ++----
> >  drivers/mfd/wm8350-i2c.c          | 24 +----------------------
> >  drivers/mfd/wm8400-core.c         | 18 +++---------------
> >  include/linux/mfd/da9052/da9052.h |  1 -
> >  26 files changed, 52 insertions(+), 407 deletions(-)
> > 
> > --
> > 2.7.4
>