[ofw] RE: Ibbus as a filter driver for mthca.

[Fab Tillier]

Hi Stan,

> Fab Tillier wrote:
>>>> 2. Attached DevTree images after clean install on a machine with one
>>>> HCA (mt25204) which has one port.
>>>>    From the images it seems that ibbus reports on the same port
>>>>    twice and mthca also report for this port. (When tested on
>>>>    machine with 2 HCA with 2 port each, 8 child objects were
>>>>    reported by ibbus and 4 by mlx4_hca) I think that mthca report
>>>>    is happen since get_relation function is still in p_ci_interface
>>>>    and mthca replies to PnP messages using this function (which
>>>> goes to ibbus
>>>> get_relation). I don't have a clue about ibbus reports.
>>>
>>> Interesting, there does seem to be duplication in reporting
>>> relations. As I remember, mthca uses the
>>> p_ci_interface->get_relations call only when mthca receives a
>>> QUERY_REMOVE_DEVICE; removal relations reporting. Since the bus
>>> driver is correctly reporting bus relations and there exists an
>>> implicit relation between the bus driver and mthca driver (same
>>> device stack, mthca cannot unload until it's instance of ibbus
>>> unloads). Possibly, the mthca driver should not be reporting
>>> relations like it does; one step closer to simple?  Do you know
>>> where in mthca relations are reported?
>>
>> This could be the problem with the reboot.  An easy work around
>> without changing mthca is to have the get_relations function return
>> without updating the child device list (basically turn it into a
>> noop).
>
> In the ibbus:fdo_query_bus_relations() call the DEVICE_QUERY_RELEATIONS
> irp needs to be completed and not passed down to the HCA driver. When
> the IRP is passed down to mthca, mthca uses the CI->get_relations upcall
> to ibbus which then reports the same relations as
> fdo_query_bus_relations reported earlier, hence the duplication of
> relations. HCA drivers should not be asked about bus relations.

Completing the request without passing it down is wrong, the whole point of these IRPs is to allow each driver in the device stack to participate as needed.  The issue with the bus driver being in the same device stack as the HCA is that devices now get reported twice - once by the bus driver, once by the HCA driver.  The relations reported by the HCA driver need to be eliminated, and there's two ways of doing this.  One is to make get_relations a noop, and leave the HCA driver unchanged.  The other is to remove bus relations processing from the HCA driver.  For the time being I would go with the first (get_relations is a noop) to minimize the changes.  Once this works well, a subsequent changeset can eliminate get_relations and the bus relations handling from the HCA drivers.

-Fab