linux-kernel - Re: [PATCH 5/6] arm64, defconfig: Enable PCI

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Message-ID: <20140925093545.GE10390@e104818-lin.cambridge.arm.com>
Date:	Thu, 25 Sep 2014 10:35:45 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Robert Richter <robert.richter@...iumnetworks.com>,
	Robert Richter <rric@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Will Deacon <Will.Deacon@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Sunil Goutham <sgoutham@...ium.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] arm64, defconfig: Enable PCI

On Wed, Sep 24, 2014 at 07:40:18PM +0100, Arnd Bergmann wrote:
> On Wednesday 24 September 2014 18:10:48 Catalin Marinas wrote:
> > On Wed, Sep 24, 2014 at 05:26:31PM +0100, Robert Richter wrote:
> > > On 24.09.14 18:14:11, Arnd Bergmann wrote:
> > > > On Wednesday 24 September 2014 17:37:47 Robert Richter wrote:
> > > > >  config PCI
> > > > >         bool "PCI support"
> > > > > +       default y
> > > > >         help
> > > > >           This feature enables support for PCIe bus system. If you say Y
> > > > >           here, the kernel will include drivers and infrastructure code
> > > > >           to support PCIe bus devices.
> > > > >  
> > > > > +config PCI_MSI
> > > > > +       def_bool PCI
> > > > > +
> > > > >  config PCI_DOMAINS
> > > > >         def_bool PCI
> > > > 
> > > > There is already a PCI_MSI symbol in drivers/pci/Kconfig. Just select that
> > > > from the PCI symbol above rather than defining a second one.
> > > 
> > > The intention is not to have a second definition, instead this should
> > > enable the default value just for arm64. Thus I put it to
> > > arch/arm64/Kconfig. Otherwise it would be enabled per default on all
> > > archs.
> 
> I don't think other architectures actually see the PCI symbol that is
> defined in the arm64 Kconfig file, but I might be wrong.

Other archs wouldn't see the symbols in arch/arm64/Kconfig.

> > > We could have used select in config ARM64, but I tried to avoid using
> > > select due to the dependency issue and instead implement this with
> > > default-y/depends-on. Doing so it can be manually disabled too.
> 
> How about adding a new symbol like
> 
> config ARM64_PCI
> 	def_bool PCI
> 	select PCI_MSI

How is this different from just selecting PCI_MSI in config PCI in
arch/arm64/Kconfig? I don't see what another symbol brings.

> > It may be better to simply set PCI and PCI_MSI as defaults in defconfig
> > rather than "default y" and an additional config PCI_MSI entry.
> 
> Selecting PCI_MSI unconditionally seems fine to me. We won't have any
> ARM64 systems that only do classic PCI, and MSI is mandatory for PCIe.

OK then, we can go with a select.

-- 
Catalin
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