linux-kernel - Re: [PATCH V4 4/7] ARM64, ACPI, PCI: I/O Remapping Table (IORT) initial support.

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Message-ID: <570F8382.6040307@arm.com>
Date:	Thu, 14 Apr 2016 12:48:18 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	okaya@...eaurora.org
Cc:	Tomasz Nowicki <tn@...ihalf.com>, tglx@...utronix.de,
	jason@...edaemon.net, rjw@...ysocki.net, lorenzo.pieralisi@....com,
	robert.richter@...iumnetworks.com, shijie.huang@....com,
	Suravee.Suthikulpanit@....com, hanjun.guo@...aro.org,
	al.stone@...aro.org, mw@...ihalf.com, graeme.gregory@...aro.org,
	Catalin.Marinas@....com, will.deacon@....com,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, ddaney.cavm@...il.com
Subject: Re: [PATCH V4 4/7] ARM64, ACPI, PCI: I/O Remapping Table (IORT)
 initial support.

On 14/04/16 12:37, okaya@...eaurora.org wrote:
> On 2016-04-14 03:36, Marc Zyngier wrote:
>> On 14/04/16 08:20, Tomasz Nowicki wrote:
>>> On 13.04.2016 23:18, Sinan Kaya wrote:
>>>> On 4/13/2016 11:52 AM, Marc Zyngier wrote:
>>>>>>> Sure. Please see:
>>>>>>> http://infocenter.arm.com/help/topic/com.arm.doc.den0049a/DEN0049A_IO_Remapping_Table.pdf
>>>>>>> 3.1.1.5 PCI root complex node
>>>>>>> PCI Segment number -> The PCI segment number, as in MCFG and as
>>>>>>> returned by _SEG in the namespace.
>>>>>>>
>>>>>>> So IORT spec states that pci_segment_number corresponds to the 
>>>>>>> segment
>>>>>>> number from MCFG table and _SEG method. Here is my patch which 
>>>>>>> makes
>>>>>>> sure pci_domain_nr(bus) is set properly:
>>>>>>> https://lkml.org/lkml/2016/2/16/418
>>>>> Lovely. So this series is actually dependent on the PCI one. I guess 
>>>>> we
>>>>> need to solve that one first, because IORT seems pretty pointless if 
>>>>> we
>>>>> don't have PCI support. What's the plan?
>>>>
>>>> Would it be OK to split the PCI specific section of the patch and 
>>>> continue
>>>> review? PCI is a user of the IORT table. Not the other way around.
>>>
>>> I need to disagree. What would be the use case for patches w/o "PCI 
>>> part" ?
>>
>> Quite. PCI (as a subsystem) doesn't need IORT at all, thank you very
>> much. GIC (implementing MSI) and SMMU (implementing DMA) do, by virtue
>> of RID/SID/DID being translated all over the place.
>>
>> So by the look of it, the dependency chain is GIC+SMMU->IORT->PCI.
>>
>> The GIC changes here are pretty mechanical, and not that interesting.
>> The stuff that needs sorting quickly is PCI, because all this work is
>> pointless if we don't have it.
>>
>> At the risk of sounding like a stuck record: What's the plan?
>>
>> Thanks,
>>
>> 	M.
> 
> My answer is based on the spec definition. The spec defines named 
> components for other peripherals that are behind iommu and can 
> potentially implement msi.
> 
> You could have used a basic device like platform sata to take care of 
> basic iort and smmu support.
> 
> You can then come back and implement PCIe support.

I could. You could do it too. Thankfully, the dependency is dictated by
whoever is writing the code.

Thanks,

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