Re: [PATCH] pci: Workaround Stratus broken PCIE hierarchy

[Prarit Bhargava <prarit@redhat.com>]

On 11/11/2011 03:35 PM, Don Dutile wrote:
> On 11/11/2011 03:29 PM, Bjorn Helgaas wrote:
>> On Fri, Nov 11, 2011 at 12:13 PM, Don Dutile<ddutile@redhat.com>  wrote:
>>> On 11/11/2011 12:41 PM, James Paradis wrote:
>>>>
>>>> Hmmm... would it be better to do this as a quirk or as a boot
>>>> parameter?  I've heard reports that other systems may be running
>>>
>>> Hearsay?  if you have definite cases, then please share them,
>>> so folks know when to flip the boot parameter on.  note: it would have to be
>>> an early boot param as well.
>>
>> It'd definitely be good to know all the specific cases.
>>
>> But merely sharing them so folks will know when to use the parameter
>> is a broken model. 

Yeah -- I'd rather do something that "works", but I'm not sure we can without dropping the only_one_child() check.

 We should make it work automatically, either with
>> some sort of machine-dependent quirk, or (preferably) with a change to
>> the generic algorithm so it can handle these "broken" topologies along
>> with all the correct ones.

The problem is when I'm examining "this" PCIE bridge I have no knowledge of the remaining hierarchy below it.  In order to find the broken topology we need to do a two pass enumeration (NO.) or minimally query all possible devices immediately connected to it.  If we do that then what is the purpose of the only_one_child() check?

> In this case, doing a check that the parent is downstream PPB and the child is
> downstream PPB could be done to identify the broken topology and automatically
> scan dev nums > 0.

I'm in favor of adding a kernel parameter that in addition to implementing the workaround Stratus will have, will also dump out a HW_ERR broken message of some sort.  I don't want to see a stack trace.

... maybe we need to add in a pci_bridge_quirk() or something?

P.