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

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Message-ID: <EE11001F9E5DDD47B7634E2F8A612F2E162435E7@lhreml503-mbs>
Date:	Wed, 14 Oct 2015 08:34:43 +0000
From:	Gabriele Paoloni <gabriele.paoloni@...wei.com>
To:	Arnd Bergmann <arnd@...db.de>
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



> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@...db.de]
> Sent: Tuesday, October 13, 2015 12:19 PM
> To: Gabriele Paoloni
> Cc: Wangzhou (B); Bjorn Helgaas; Bjorn Helgaas; jingoohan1@...il.com;
> pratyush.anand@...il.com; linux@....linux.org.uk;
> thomas.petazzoni@...e-electrons.com; lorenzo.pieralisi@....com;
> james.morse@....com; Liviu.Dudau@....com; jason@...edaemon.net;
> robh@...nel.org; gabriel.fernandez@...aro.org;
> Minghuan.Lian@...escale.com; linux-pci@...r.kernel.org; linux-arm-
> kernel@...ts.infradead.org; devicetree@...r.kernel.org; linux-
> kernel@...r.kernel.org; zhangjukuo; qiuzhenfa; liudongdong (C);
> qiujiang; xuwei (O); Liguozhu (Kenneth); Wangkefeng (Kevin); Rob
> Herring
> Subject: Re: [PATCH v10 4/6] PCI: hisi: Add PCIe host support for
> HiSilicon SoC Hip05
> 
> On Tuesday 13 October 2015 06:58:42 Gabriele Paoloni wrote:
> >
> > > >> +
> > > >> +static int __init hisi_pcie_init(void)
> > > >> +{
> > > >> +	return platform_driver_probe(&hisi_pcie_driver,
> hisi_pcie_probe);
> > > >> +}
> > > >> +subsys_initcall(hisi_pcie_init);
> > > >
> > > > Can you use module_platform_driver() or
> module_platform_driver_probe()
> > > > here instead of the subsys_initcall()?  No, I don't really know
> what
> > > > the difference between module_platform_driver() and
> > > > module_platform_driver_probe() is, sorry :)
> 
> module_platform_driver_probe() will only call the probe function once
> (and fail in case of -EPROBE_DEFER), while module_platform_driver()
> installs the platform driver in a way that the device can be bound
> and unbound at any point.
> 
> > > In fact, I used module_platform_driver_probe in previous version,
> but
> > > A PCIe VGA card of HiSilicon will use Hip05 PCIe host, so we
> modified
> > > module_platform_driver_probe to subsys_initcall which will be
> called
> > > before module_platform_driver_probe.
> > >
> > > We will upstream the driver of above PCIe VGA card soon.
> 
> I don't see a reason why a VGA driver would need the PCI host to be
> probed this early, unless it is the only usable console in the system.
> 
> > Hi Bjorn, firstly many thanks for looking at this.
> >
> > About this last bit the reason why we use subsys_initcall() is that
> > our host bridge is embedded in the SoC and as such is not hot-
> pluggable
> > for instance see:
> > http://lxr.free-electrons.com/source/Documentation/driver-
> model/platform.txt#L59
> 
> We should still be able to build the driver as a loadable module,
> even if you don't do that on your own kernels.

Hi Arnd, I don't see the point of having loadable KOs for platform
devices that are integrated into SoCs (like PCIe Host Controllers...)

> 
> This doesn't mean that it has to be module_platform_driver,
> subsys_initcall
> will also work in a loadable module, it just won't be as early. However,
> we should try to come up with a consistent approach for all PCI host
> drivers,
> I don't see any reason for hisi to be different from the others here.

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?

Thanks

Gab

> 
> > Our approach is also used by Exynos:
> > http://lxr.free-electrons.com/source/drivers/pci/host/pci-
> exynos.c#L644
> 
> Maybe we should change that too.
> 
> 	Arnd
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