linux-kernel - Re: [PATCH v2 06/22] PCI/MSI: Introduce weak arch_find_msi

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Date:	Fri, 26 Sep 2014 10:33:24 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Bjorn Helgaas <bhelgaas@...gle.com>, <linux-pci@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Xinwei Hu <huxinwei@...wei.com>,
	Wuyun <wuyun.wu@...wei.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King <linux@....linux.org.uk>,
	<linux-arch@...r.kernel.org>, <arnab.basu@...escale.com>,
	<Bharat.Bhushan@...escale.com>, <x86@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	<xen-devel@...ts.xenproject.org>, Joerg Roedel <joro@...tes.org>,
	<iommu@...ts.linux-foundation.org>, <linux-mips@...ux-mips.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-s390@...r.kernel.org>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	"Tony Luck" <tony.luck@...el.com>, <linux-ia64@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	<sparclinux@...r.kernel.org>, Chris Metcalf <cmetcalf@...era.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Lucas Stach <l.stach@...gutronix.de>,
	David Vrabel <david.vrabel@...rix.com>,
	"Sergei Shtylyov" <sergei.shtylyov@...entembedded.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Thierry Reding <thierry.reding@...il.com>,
	"Thomas Petazzoni" <thomas.petazzoni@...e-electrons.com>
Subject: Re: [PATCH v2 06/22] PCI/MSI: Introduce weak arch_find_msi_chip()
 to find MSI chip

On 2014/9/25 18:38, Thomas Gleixner wrote:
> On Thu, 25 Sep 2014, Yijing Wang wrote:
> 
>> Introduce weak arch_find_msi_chip() to find the match msi_chip.
>> Currently, MSI chip associates pci bus to msi_chip. Because in
>> ARM platform, there may be more than one MSI controller in system.
>> Associate pci bus to msi_chip help pci device to find the match
>> msi_chip and setup MSI/MSI-X irq correctly. But in other platform,
>> like in x86. we only need one MSI chip, because all device use
>> the same MSI address/data and irq etc. So it's no need to associate
>> pci bus to MSI chip, just use a arch function, arch_find_msi_chip()
>> to return the MSI chip for simplicity. The default weak
>> arch_find_msi_chip() used in ARM platform, find the MSI chip
>> by pci bus.
> 
> This is really backwards. On one hand you try to get rid of the weak
> arch functions zoo and then you invent new ones for no good
> reason. Why can't x86 store the chip in the pci bus?

Hi Thomas, I introduced this weak function , because I thought all platforms
except arm always have only one msi chip, and I hoped to provide a simplest
solution, less code changes. I consider several solutions to associate msi chip
and PCI device. In my reply to Thierry in first reply,
http://marc.info/?l=linux-pci&m=141169658208255&w=2
Could you give me some advices ?

Thanks!
Yijing.


> 
> Looking deeper, I'm questioning the whole notion of different
> msi_chips. Are this really different MSI controllers with a different
> feature set or are this defacto multiple instances of the same
> controller which just need a different data set?
> 
> Thanks,
> 
> 	tglx
> 
> .
> 


-- 
Thanks!
Yijing

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