linux-kernel - Re: [RFC PATCH 3/3] dt-bindings: pci: xgene pcie device tree bindings

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Date:	Thu, 9 Jan 2014 17:32:13 -0800
From:	Tanmay Inamdar <tinamdar@....com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Arnd Bergmann <arnd@...db.de>, devicetree@...r.kernel.org,
	Jon Masters <jcm@...hat.com>, linux-doc@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	patches <patches@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Landley <rob@...dley.net>, linux-pci@...r.kernel.org,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH 3/3] dt-bindings: pci: xgene pcie device tree bindings

On Tue, Jan 7, 2014 at 10:31 AM, Jason Gunthorpe
<jgunthorpe@...idianresearch.com> wrote:
> On Tue, Jan 07, 2014 at 04:35:01PM +0100, Arnd Bergmann wrote:
>
>> > >> +                       0x00000000 0x0 0xd0000000 0xe0 0xd0000000 0x0 0x00200000 /* cfg */
>> > >
>> > > config space is not normally in the ranges property, and I think you will need
>> > > it in the pcie node itself as a 'reg' property so the code can access it.
>> >
>> > pcie-designware.c does it that way. I just followed their implementation.
>>
>> I don't remember what led to that, it still seems wrong and I can't
>> find anything in the PCI binding for host bridges telling their
>> config space this way.
>
> When we discussed the mvebu PCI driver (which is, so far, the most
> throughly discussed PCI binding) it was concluded that the config
> space ranges like the above was OK only if it exactly described the
> standard ECAM layout.
>
> Idea being that standard/core code should be able to see that ranges,
> map the range and issue config accesses via the ECAM rules.

Ok. Thanks.

>
>> > >> +             interrupt-map-mask = <0x0 0x0 0x0 0x7>;
>> > >> +             interrupt-map = <0x0 0x0 0x0 0x1 &gic 0x0 0xc2 0x1>;
>> > >
>> > > Only one IRQ for all devices?
>> >
>> > The node represents a port. I believe that Linux framework uses only
>> > one of the legacy IRQs per port. Rest all remain unused. Hence I
>> > removed them. Please correct me if I am wrong.
>>
>> Any PCI device can normally have four interrupts (IntA through
>> IntD), which are traditionally separate pins on a PCI bus, but get
>> emulated on PCIe. While it's not common for any normal device to use
>> more than one IRQ, a bridge device will swizzle these (virtual) IRQ
>> lines, so a device behind the bridge actually gets a different host
>> IRQ.
>
> Agree, the binding should handle all four INTA,B,C,D assertions
> delivered to the port.
>
> If HW is able to decode the 4 ints into seperate Linux interrupt
> numbers then that should be described. If HW routes them all to a
> single number then interrupt-map-mask should be all 0.
>
> Arnd's point about swizzling effects the layout of the
> interrupt-map. When it is placed at the pcie-controller node level the
> map will incorporate one swizzle of the on-the-wire INTx messages. If
> the HW doesn't swizzle the INTx as the TLP passes through the bridge
> then it probably makes more sense to put the interrupt-map in the DT
> node of the bridge like mvebu does.
>

Ok.

> Jason
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