linux-kernel - Re: [PATCH v10 4/6] PCI: hisi: Add PCIe host support for HiSilicon SoC Hip05

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Date:	Wed, 14 Oct 2015 11:42:27 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Gabriele Paoloni <gabriele.paoloni@...wei.com>
Cc:	"Wangzhou (B)" <wangzhou1@...ilicon.com>,
	Bjorn Helgaas <helgaas@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"jingoohan1@...il.com" <jingoohan1@...il.com>,
	"pratyush.anand@...il.com" <pratyush.anand@...il.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"thomas.petazzoni@...e-electrons.com" 
	<thomas.petazzoni@...e-electrons.com>,
	"lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
	"james.morse@....com" <james.morse@....com>,
	"Liviu.Dudau@....com" <Liviu.Dudau@....com>,
	"jason@...edaemon.net" <jason@...edaemon.net>,
	"robh@...nel.org" <robh@...nel.org>,
	"gabriel.fernandez@...aro.org" <gabriel.fernandez@...aro.org>,
	"Minghuan.Lian@...escale.com" <Minghuan.Lian@...escale.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	zhangjukuo <zhangjukuo@...wei.com>,
	qiuzhenfa <qiuzhenfa@...ilicon.com>,
	"liudongdong (C)" <liudongdong3@...wei.com>,
	qiujiang <qiujiang@...wei.com>,
	"xuwei (O)" <xuwei5@...ilicon.com>,
	"Liguozhu (Kenneth)" <liguozhu@...ilicon.com>,
	"Wangkefeng (Kevin)" <wangkefeng.wang@...wei.com>,
	Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v10 4/6] PCI: hisi: Add PCIe host support for HiSilicon SoC Hip05

On Wednesday 14 October 2015 09:31:48 Gabriele Paoloni wrote:
> > 
> > > To me it sounds more appropriate to adopt subsys_initcall() for all
> > the
> > > PCI Host Bridge controllers rather than having them as loadable
> > modules...
> > >
> > > What is your view?
> > 
> > subsys_initcall() sounds odd because it's a driver rather than a
> > subsystem,
> > but I realize that most of the other levels don't fit any better.
> 
> Yes well I was seeing for example the vgaarb 
> http://lxr.free-electrons.com/source/drivers/gpu/vga/vgaarb.c#L1357
> 
> That in the init is calling pci_get_subsys()
> 
> So I was wondering that the PCI devices may not be registered unless
> we also init the PCI host bridge through subsys_initcall()...

I think this should work as is: the code first looks for devices
that are already there and then registers a notifier for devices
that show up later. This is meant to work for both devices that
are hotplugged at a later point as well as PCI buses that are
already there but not yet probed.

> But then maybe is the vgaarb to be buggy...

Possible. It may well be that the code is only tested on x86,
which always probes its PCI very early.

> > As I said, it's not really a choice we have to make in the source code,
> > we can use subsys_initcall together with module_exit(), or we can
> > create a helper macro that is similar to module_platform_driver()
> > specifically for PCI that uses a particular initcall level.
> 
> Ok got it. But I guess this needs to be thought and applied to all
> the PCI host bridge controllers...
> 
> So maybe for this driver I can use module_platform_driver_probe()
> and then we can see...

Sounds good. Let's focus on getting the driver merged first and
then follow up with a patch to get this right for all PCI hosts.

	Arnd
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