linux-kernel - Re: [PATCH 00/10] drivers/pci: avoid module

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Message-ID: <20151214082425.GA3766@ulmo.nvidia.com>
Date:	Mon, 14 Dec 2015 09:24:25 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Paul Gortmaker <paul.gortmaker@...driver.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	linux-pci <linux-pci@...r.kernel.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Pratyush Anand <pratyush.anand@...il.com>,
	Michal Simek <michal.simek@...inx.com>,
	Kishon Vijay Abraham I <kishon@...com>,
	Murali Karicheri <m-karicheri2@...com>,
	Sören Brinkmann <soren.brinkmann@...inx.com>,
	Jason Cooper <jason@...edaemon.net>,
	Stephen Warren <swarren@...dotorg.org>,
	Simon Horman <horms@...ge.net.au>, linux-tegra@...r.kernel.org,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Richard Zhu <Richard.Zhu@...escale.com>,
	rfi@...ts.rocketboards.org, Ley Foon Tan <lftan@...era.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Lucas Stach <l.stach@...gutronix.de>
Subject: Re: [PATCH 00/10] drivers/pci: avoid module_init in non-modular
 host/pci*

On Mon, Dec 14, 2015 at 09:19:30AM +0100, Geert Uytterhoeven wrote:
> Hi Paul,
> 
> On Sun, Dec 13, 2015 at 2:41 AM, Paul Gortmaker
> <paul.gortmaker@...driver.com> wrote:
> > This series of commits is a slice of a larger project to ensure
> > people don't have dead code for module removal in non-modular
> > drivers.  Overall there was roughly 5k lines of dead code in the
> > kernel due to this.  So far we've fixed several areas, like tty,
> > x86, net, etc. and we continue to work on other areas.
> >
> > There are several reasons to not use module_init for code that can
> > never be built as a module, but the big ones are:
> >
> >  (1) it is easy to accidentally code up 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.
> >
> > Here we convert some module_init() calls into device_initcall() and delete
> > any module_exit and remove code that gets orphaned in the process, for
> > an overall net code reduction, which is always welcome.
> >
> > The use of device_initcall ensures that the init function ordering
> > remains unchanged, but one could argue that PCI host code might be more
> > appropriate to be handled under subsys_initcall.  Fortunately we can
> > revisit making this extra change at a later date if desired; it does
> > not need to happen now, and we reduce the risk of introducing
> > regressions at this point in time by separating the two changes.
> >
> > Over half of the drivers changed here already explicitly disallowed any
> > unbind operations.  For the rest we make them the same, since there is
> > not really any sensible use case to unbind any built-in bus support that
> > I can think of.
> 
> Personally, I think all of these should become tristate, so distro kernels
> don't have to build in PCI(e) support for all SoCs. multi_v7_defconfig kernels
> are becoming too big.
> 
> That does not preclude making these modules un-unloadable, though.

Most of these can't be made tristate as-is, because they use symbols
that aren't exported. Many of those symbols can easily be exported, so
its just a matter of getting the respective patches merged. I disagree
with making the modules non-unloadable, though. I have a local branch
with changes necessary to unload the host controller driver and it
works just fine.

Thierry

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