linux-kernel - Re: [PATCH v3 00/15] Introducing per-device MSI domain

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Message-ID: <559FD5BC.9070206@arm.com>
Date:	Fri, 10 Jul 2015 15:25:00 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Jason Cooper <jason@...edaemon.net>,
	"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>,
	Yijing Wang <wangyijing@...wei.com>,
	Ma Jun <majun258@...wei.com>
Subject: Re: [PATCH v3 00/15] Introducing per-device MSI domain

On 10/07/15 14:34, Lorenzo Pieralisi wrote:
> On Thu, Jul 09, 2015 at 03:35:05PM +0100, Marc Zyngier wrote:
> 
> [...]
> 
>>> BTW, is there a reason why _all_ arm host bridges rely on
>>> pcibios_msi_controller (so pci_sys_data) instead of initializing
>>> the struct pci_bus.msi pointer to carry out the MSI controller look-up ?
>>
>> Probably an ordering issue - the bus may not be there yet. But ensuring
>> that the MSI domain is created early (before the bus is scanned) should
>> solve that problem nicely enough.
> 
> Yes, I think the only reason is that, as sysdata, the msi controller
> pointer is propagated (in pci_alloc_child_bus()), with a tiny difference:
> sysdata can be passed to pci_scan_root_bus(), msi controller pointer
> can't (explicitly) at present.
> 
> Since most of the ARM PCI host controllers have been converted to:
> 
> - pci_create_root_bus()
> 
> -> here we can init bus msi controller pointer
> 
> - pci_scan_child_bus()
> 
> we could get rid of pcibios_msi_controller on arm _now_ by just initializing
> the msi controller pointer in the struct pci_bus before
> pci_scan_child_bus() is called, unless I am missing something.
> 
> I converted pcie-designware.c to stacked domains (and pci-keystone that
> relies on it, with its own quirks of course), I might take the step
> above as an intermediate step to have a common arm/arm64 generic host
> controller asap (ie for that getting rid of pcibios_msi_controller is
> mandatory, which requires converting all ARM host controllers to stacked
> domains, or taking the intermediate step above).

It doesn't look like the two approaches are incompatible. Killing
pcibios_msi_controller is an interesting short term goal which could
happen quite quickly. Converting these host controllers to stacked
domains is obviously more effort, which can happen at its own pace. We
just need to make sure people do not add more cruft to the mix in the
meantime.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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