linux-kernel - Re: Kirkwood PCI Express and bridges

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Date:   Fri, 21 Jun 2019 07:33:18 +0200
From:   Thomas Petazzoni <thomas.petazzoni@...tlin.com>
To:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>
Cc:     Jason Cooper <jason@...edaemon.net>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        "Bjorn Helgaas" <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Kirkwood PCI Express and bridges

Hello Chris,

On Fri, 21 Jun 2019 04:03:27 +0000
Chris Packham <Chris.Packham@...iedtelesis.co.nz> wrote:

> I'm in the process of updating the kernel version used on our products 
> from 4.4 -> 5.1.
> 
> We have one product that uses a Kirkwood CPU, IDT PCI bridge and Marvell 
> Switch ASIC. The Switch ASIC presents as multiple PCI devices.
> 
> The hardware setup looks like this
>                                         __________
> [ Kirkwood ] --- [ IDT 5T5 ] ---+---  |          |
>                                  +---  |  Switch  |
>                                  +---  |          |
>                                  +---  |__________|
> 
> On the 4.4 based kernel things are fine
> 
> [root@...lus flash]# lspci -t
> -[0000:00]---01.0-[01-06]----00.0-[02-06]--+-02.0-[03]----00.0
>                                             +-03.0-[04]----00.0
>                                             +-04.0-[05]----00.0
>                                             \-05.0-[06]----00.0
> 
> But on the 5.1 based kernel things get a little weird
> 
> [root@...lus flash]# lspci -t
> -[0000:00]---01.0-[01-06]--+-00.0-[02-06]--
>                             +-01.0
>                             +-02.0-[02-06]--
>                             +-03.0-[02-06]--
>                             +-04.0-[02-06]--
>                             +-05.0-[02-06]--
>                             +-06.0-[02-06]--
>                             +-07.0-[02-06]--
>                             +-08.0-[02-06]--
>                             +-09.0-[02-06]--
>                             +-0a.0-[02-06]--
>                             +-0b.0-[02-06]--
>                             +-0c.0-[02-06]--
>                             +-0d.0-[02-06]--
>                             +-0e.0-[02-06]--
>                             +-0f.0-[02-06]--
>                             +-10.0-[02-06]--
>                             +-11.0-[02-06]--
>                             +-12.0-[02-06]--
>                             +-13.0-[02-06]--
>                             +-14.0-[02-06]--
>                             +-15.0-[02-06]--
>                             +-16.0-[02-06]--
>                             +-17.0-[02-06]--
>                             +-18.0-[02-06]--
>                             +-19.0-[02-06]--
>                             +-1a.0-[02-06]--
>                             +-1b.0-[02-06]--
>                             +-1c.0-[02-06]--
>                             +-1d.0-[02-06]--
>                             +-1e.0-[02-06]--
>                             \-1f.0-[02-06]--+-02.0-[03]----00.0
>                                             +-03.0-[04]----00.0
>                                             +-04.0-[05]----00.0
>                                             \-05.0-[06]----00.0
> 
> 
> I'll start bisecting to see where things started going wrong. I just 
> wondered if this rings any bells for anyone.

I am almost sure that the culprit is
1f08673eef1236f7d02d93fcf596bb8531ef0d12 ("PCI: mvebu: Convert to PCI
emulated bridge config space").

I still think it makes sense to share the bridge emulation code between
the mvebu and aardvark drivers, but this sharing has required making
the code very different, with lots of subtle differences in behavior in
how registers are emulated.

Unfortunately, I don't have access to one of these complicated PCI
setup with a HW switch on the way, so I couldn't test this kind of
setups.

Do you mind helping with figuring out what the issues are ? That would
be really nice.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com