linux-kernel - Re: [Patch v4 5/8] ARM64/PCI/ACPI: Introduce struct pci

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Message-ID: <20150603100343.GA27917@red-moon>
Date:	Wed, 3 Jun 2015 11:03:43 +0100
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
Cc:	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Yijing Wang <wangyijing@...wei.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	Lv Zheng <lv.zheng@...el.com>,
	"lenb @ kernel . org" <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"x86 @ kernel . org" <x86@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [Patch v4 5/8] ARM64/PCI/ACPI: Introduce struct pci_controller
 for ACPI

On Wed, Jun 03, 2015 at 10:36:19AM +0100, Jiang Liu wrote:
> On 2015/6/3 16:44, Hanjun Guo wrote:
> > On 2015???06???02??? 17:35, Lorenzo Pieralisi wrote:
> >> On Tue, Jun 02, 2015 at 07:12:53AM +0100, Jiang Liu wrote:
> >>> From: Hanjun Guo <hanjun.guo@...aro.org>
> >>>
> >>> ARM64 ACPI based PCI host bridge init needs a arch dependent
> >>> struct pci_controller to accommodate common PCI host bridge
> >>> code which is introduced later, or it will lead to compile
> >>> errors on ARM64.
> >>>
> >>> Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org>
> >>> Tested-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
> >>> CC: Arnd Bergmann <arnd@...db.de>
> >>> CC: Catalin Marinas <catalin.marinas@....com>
> >>> CC: Liviu Dudau <Liviu.Dudau@....com>
> >>> CC: Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>
> >>> CC: Will Deacon <will.deacon@....com>
> >>> Signed-off-by: Jiang Liu <jiang.liu@...ux.intel.com>
> >>> ---
> >>>   arch/arm64/include/asm/pci.h |   10 ++++++++++
> >>>   1 file changed, 10 insertions(+)
> >>>
> >>> diff --git a/arch/arm64/include/asm/pci.h b/arch/arm64/include/asm/pci.h
> >>> index b008a72f8bc0..70884957f253 100644
> >>> --- a/arch/arm64/include/asm/pci.h
> >>> +++ b/arch/arm64/include/asm/pci.h
> >>> @@ -10,6 +10,16 @@
> >>>   #include <asm-generic/pci-bridge.h>
> >>>   #include <asm-generic/pci-dma-compat.h>
> >>>
> >>> +struct acpi_device;
> >>> +
> >>> +struct pci_controller {
> >>> +#ifdef CONFIG_ACPI
> >>> +    struct acpi_device *companion;    /* ACPI companion device */
> >>> +#endif
> >>> +    int        segment;    /* PCI domain */
> >>> +    int        node;        /* NUMA node */
> >>> +};
> >>
> >> There is nothing ARM64 specific in this structure. The only
> >> reason I see you want to keep it arch specific is the iommu
> >> pointer on x86,
> > 
> > And also plarform_data for IA64 too.
> > 
> >> but I think we should find a way to make
> >> the common bits shared across archs (ie the struct above) and
> >> add (maybe a void*) to the generic struct to cater for arch
> >> specific data.
> >>
> >> Thoughts ?
> > 
> > We discussed this already, it has limitations to make it
> > common to all archs, I think the limitation are:
> > 
> >   - struct pci_controller are also used for other archs
> >     such as PowerPC and Tile, they will not use it for
> >     ACPI purpose, so we can not used for all archs.
> > 
> >   - if we let struct pci_controller defined only for archs
> >     using ACPI, such as introduce it in linux/acpi.h, we still
> >     can not satisfy that the struct pci_controller is not
> >     only used for ACPI case on x86, it will be used for
> >     non-ACPI too.
> > 
> > So it's pretty difficult to share it with across archs to me,
> > any more ideas?
> Hi Hanjun and Lorenzo,
> 	As mentioned by Hanjun, I have no idea yet about how to
> consolidating "struct pci_controller" further. One possible
> way is to move "struct pci_controller" related code into
> arch, but apparently that will reduce code reusing.

I guess you can't move that struct pci_controller to generic code
since it is present on other archs too (with completely different
members).

What you can do is creating a new struct (ie same purpose of pci_controller
with a different name) common to all archs that contains the common bits
+ a void* data that contains arch specific data, and convert x86 and ia64
to using it.

It is weird to be forced to declare a pci_controller structure in arm64
code with 0 arch specific data in it.

Lorenzo
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