linux-kernel - Re: [RFC PATCH 2/3] arm64: dts: APM X-Gene PCIe device tree nodes

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Date:	Thu, 9 Jan 2014 17:30:43 -0800
From:	Tanmay Inamdar <tinamdar@....com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Grant Likely <grant.likely@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Rob Landley <rob@...dley.net>, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-pci@...r.kernel.org,
	patches <patches@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jon Masters <jcm@...hat.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH 2/3] arm64: dts: APM X-Gene PCIe device tree nodes

On Tue, Jan 7, 2014 at 9:27 AM, Jason Gunthorpe
<jgunthorpe@...idianresearch.com> wrote:
> On Mon, Jan 06, 2014 at 06:56:21PM -0800, Tanmay Inamdar wrote:
>
>> > There is some kind of an addressing problem because you've done this:
>> >
>> > +static void xgene_pcie_fixup_bridge(struct pci_dev *dev)
>> > +{
>> > +       int i;
>> > +
>> > +       for (i = 0; i < DEVICE_COUNT_RESOURCE; i++) {
>> > +               dev->resource[i].start = dev->resource[i].end = 0;
>> > +               dev->resource[i].flags = 0;
>> > +       }
>> > +}
>> > +DECLARE_PCI_FIXUP_HEADER(XGENE_PCIE_VENDORID, XGENE_PCIE_BRIDGE_DEVICEID,
>> > +                        xgene_pcie_fixup_bridge);
>> >
>> > Which is usually a sign that something is wonky with how the HW is
>> > being fit into the PCI core.
>>
>> We map the whole DDR range (eg 256 GB) into host's BAR. The Linux PCI
>> resource management tries to fit the host's memory into the ranges
>> provided (eg 0xe000000000).
>> Please let me know if there is any use case to do this mapping.
>
> If you need to set the bridge's BAR like this, then the bridge is not
> non-conforming.. Bridge BAR's should be 0 size unless the bridge
> itself has registers.

They are not set to 0 as per our hardware implementation. We have to
hide it using the fixup API. I don't know the reason but
"arch/powerpc/sysdev/xilinx_pci.c" is doing the same thing.

>
> Do any registers in this config space work properly? Does the
> secondary status reflect the physical link status properly?

Link status information is seen correctly.

>
> If it is *really* broken you might just consider hiding it from the
> Linux core.
>
>> >>         Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort-
>> >> <TAbort- <MAbort- >SERR- <PERR- INTx-
>> >>         Latency: 0, Cache Line Size: 64 bytes
>> >>         Region 0: Memory at <ignored> (64-bit, prefetchable)
>> >>         Bus: primary=00, secondary=01, subordinate=01, sec-latency=0
>> >>         I/O behind bridge: 0000f000-00000fff
>> >>         Memory behind bridge: 00c00000-00cfffff
>> >
>> > [..]
>> >
>> >> 01:00.0 Class 0200: Device 15b3:1003
>> >>         Region 0: Memory at e000c00000 (64-bit, non-prefetchable) [size=1M]
>> >>         Region 2: Memory at e000000000 (64-bit, prefetchable)
>> >>         [size=8M]
>> >
>> > Something funky is going on here too, the 64 bit address e000000000
>> > should be reflected in the 'memory behind bridge' above, not
>> > truncated.
>>
>> That's the Mellanox device that is plugged into the system. The
>> device's memory gets mapped at '0xe0xxxxxxxx'
>
> Right, but the bridge setup above has:
>
>> >>         Memory behind bridge: 00c00000-00cfffff
>
> Which is wrong, it doesn't include the range '0xe0xxxxxxxx'
>
> Jason
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