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

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Message-ID: <20140107172734.GC4227@obsidianresearch.com>
Date:	Tue, 7 Jan 2014 10:27:34 -0700
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Tanmay Inamdar <tinamdar@....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 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.

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

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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