linux-kernel - Re: [PATCH] arch: powerpc: pci-common: fix wrong return value check on phd

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Message-ID: <CALJn8nPbTy3Ne2a7L71c2YZ06Ccr2j0zs6TdptfRc7O-N9u=Yg@mail.gmail.com>
Date:   Tue, 19 Jun 2018 12:29:41 -0300
From:   Guilherme Piccoli <kernel@...ccoli.net>
To:     Daniel Walker <danielwa@...co.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        xe-kernel@...ernal.cisco.com,
        Gavin Shan <gwshan@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
        Ian Munsie <imunsie@....ibm.com>,
        linuxppc-dev@...ts.ozlabs.org,
        Mauro Rodrigues <maurosr@...ux.vnet.ibm.com>
Subject: Re: [PATCH] arch: powerpc: pci-common: fix wrong return value check
 on phd_id

On Mon, Jun 18, 2018 at 1:57 PM, Daniel Walker <danielwa@...co.com> wrote:
> Cisco has a couple platforms which depend on the domain values getting
> set a certain way. We discovered our machines not detecting the pci
> devices, and traced it back to this commit,
>
> 63a7228 powerpc/pci: Assign fixed PHB number based on device-tree
> properties
>
> It seems that the code is expecting the return value of of_property_read_u64()
> to be the opposite of what it actually is.. It returns zero on success, and a
> negative return value on error. So if you only check when it's non-zero your
> going to set Opal for all platforms but Opal, which I assume is not what was
> expected.

Hi Daniel, thanks for exposing a potential issue and trying to fix.
(And thanks Mauro to point this message, since my email changed).

I disagree with your patch Daniel, I think it's wrong.
Since the logic of my original patch is kind of convoluted, for improve
(even my own) understanding, I tried to over-comment the logic here:
https://pastebin.ubuntu.com/p/4DNvd9b2bY

Please, take a look and see if you agree with the logic now.

Regarding your issue, I'm interested - I think perhaps you have some FW
flaw that might be exposing duplicated "reg" or "ibm,opal-phbid" properties.
Or maybe you somehow rely on the old incremental PHB setting and your
software stack is not working properly with the DT-based PHB values.

Please, elaborate the issue a bit more in order we can try to figure
out. And also, you could try reverting the below two patches and boot
the kernel to be sure it works:

61e8a0d5a02 powerpc/pci: Fix endian bug in fixed PHB numbering
63a72284b15 powerpc/pci: Assign fixed PHB number based on device-tree properties

*Notice* the first is a fix to my patch, and both should be tested together.
Be sure your current kernel has _both or neither_ these patches!

Cheers,

Guilherme