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

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Date:	Mon, 14 Dec 2015 16:33:51 +0800
From:	Ley Foon Tan <lftan@...era.com>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	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>,
	Rocketboard Maillist <rfi@...ts.rocketboards.org>,
	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 4:24 PM, Thierry Reding
<thierry.reding@...il.com> wrote:
> 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.
>
PCIe host driver that use fixup (DECLARE_PCI_FIXUP_*) can't use tristate.
Fixup region is in kernel region and this region if not updated when
loading a module.

Regards
Ley Foon
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