linux-kernel - Re: [PATCH v2 00/22] Use MSI chip framework to configure MSI/MSI-X in all platforms

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Message-ID: <20140926085030.GE31157@bart.dudau.co.uk>
Date:	Fri, 26 Sep 2014 09:50:30 +0100
From:	Liviu Dudau <liviu@...au.co.uk>
To:	Yijing Wang <wangyijing@...wei.com>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	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>,
	Thomas Gleixner <tglx@...utronix.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>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Subject: Re: [PATCH v2 00/22] Use MSI chip framework to configure MSI/MSI-X
 in all platforms

On Fri, Sep 26, 2014 at 11:42:23AM +0800, Yijing Wang wrote:
> >> I am actually in disagreement with you, Thierry. I don't like the general direction
> >> of the patches, or at least I don't like the fact that we don't have a portable
> >> way of setting up the msi_chip without having to rely on weak architectural hooks.
> > 
> > Oh, good. That's actually one of the things I said I wasn't happy with
> > either. =)
> 
> Hm, I decide to drop weak arch_find_msi_chip(), no one likes it.
> Let's find a better solution :)
> 
> > 
> >> I'm surprised no one considers the case of a platform having more than one host
> >> bridge and possibly more than one MSI unit. With the current proposed patchset I
> >> can't see how that would work.
> > 
> > The PCI core can already deal with that. An MSI chip can be set per bus
> > and the weak pcibios_add_bus() can be used to set that. Often it might
> > not even be necessary to do it via pcibios_add_bus() if you create the
> > root bus directly, since you can attach the MSI chip at that time.
> 
> Yes, PCI hostbridge driver find the matched msi chip during its initialization,
> and assign the msi chip to PCI bus in pcibios_add_bus().
> 
> > 
> >> What I would like to see is a way of creating the pci_host_bridge structure outside
> >> the pci_create_root_bus(). That would then allow us to pass this sort of platform
> >> details like associated msi_chip into the host bridge and the child busses will
> >> have an easy way of finding the information needed by finding the root bus and then
> >> the host bridge structure. Then the generic pci_scan_root_bus() can be used by (mostly)
> >> everyone and the drivers can remove their kludges that try to work around the
> >> current limitations.
> 
> So I think maybe save msi chip in PCI arch sysdata is a good candidate.

Except that arch sysdata at the moment is an opaque pointer. I am all in favour in
changing the type of sysdata from void* into pci_host_bridge* and arches can wrap their old
sysdata around the pci_host_bridge*.

Best regards,
Liviu

> 
> > 
> > I think both issues are orthogonal. Last time I checked a lot of work
> > was still necessary to unify host bridges enough so that it could be
> > shared across architectures. But perhaps some of that work has
> > happened in the meantime.
> > 
> > But like I said, when you create the root bus, you can easily attach the
> > MSI chip to it.
> > 
> > Thierry
> > 
> 
> 
> -- 
> Thanks!
> Yijing
> 
> 

-- 
-------------------
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   (   )
    \ (  Oooo.
     \_) (   )
          ) /
         (_/

 One small step
   for me ...

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