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

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Date:   Tue, 19 Jun 2018 09:57:15 -0700
From:   Daniel Walker <danielwa@...co.com>
To:     "Guilherme G. Piccoli" <guilherme@...ccoli.net>,
        mpe@...erman.id.au, benh@...nel.crashing.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        xe-kernel@...ernal.cisco.com, linux-kernel@...r.kernel.org,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org,
        Mauro Rodrigues <maurosr@...ux.vnet.ibm.com>,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH] arch: powerpc: pci-common: fix wrong return value check
 on phd_id

On 06/19/2018 09:26 AM, Guilherme G. Piccoli wrote:
>> [...]
>> What your doing is changing the phb_id to some transformation of "reg" for
>> all platforms except which have "ibm,opal-phbid". This is what we observe.
>> This is a radical altering of the prior phb_id selection before your patch.
>>
>> The question is, was that your intent ? We are expecting these numbers
>> aren't getting altered in this way, this is why we have the patch. Your
>> patch description appears to suggest you want this type of selection for
>> "... pSeries and PowerNV cases)." , so I am assuming you did this by
>> mistake. Also I don't see a reason to make this change for all platforms.
> It was the intent - whenever we have device-tree information, the idea is to
> use it to have more consistent numbering across reboots and PCI hotplugs.
> The reason to change that originally is hotplugging a PCI device added
> the device with a different PHB/Domain value, and network predictable naming
> messed-up interfaces' names, leading to a machine without networking.

Ok ..

>
>
>> [...]
>>
>> We have already done this, that is how we determined your patch was changing
>> the domain values. There isn't much to tell w.r.t this issue on our side, we
>> are expecting the domain numbers are set a specific way and they aren't
>> getting set that way. The drivers which are looking for PCI devices are not
>> in kernel space, and the PCI domain values are getting taken from userspace.
>>
> Oh okay, I imagined it was some crazy userspace-based PCI domain scheme
> that led you to report the issue - confirmed heheh
> So, you expect the old behavior right? Incremental PHB numbering.
> I think we could have a kernel config option to allow that, this way
> you could rebuild your kernel with that option and keep the old behavior.
>
> This idea needs to be validated by the maintainers, or perhaps they could
> propose another way to keep the old behavior to interested parties.
>
> [Looping linux-pci too - original thread at:
> https://lists.ozlabs.org/pipermail/linuxppc-dev/2018-June/174760.html]

I didn't look into changing the behavior on our side because it didn't 
look like the intent of the patch was to make a global change. I can 
take a look at changing this behavior on our side , given that this was 
intended by your changes.

However, they're may be other platforms or drivers which depend on these 
numbers getting set a certain way, so there may be other userspace 
dependencies on these values.

Daniel