[PATCH 03/15] powerpc/powernv/pci: Add explicit tracking of the DMA setup state

[Alexey Kardashevskiy]

On 14/07/2020 17:21, Alexey Kardashevskiy wrote:
> 
> 
> On 14/07/2020 15:58, Oliver O'Halloran wrote:
>> On Tue, Jul 14, 2020 at 3:37 PM Alexey Kardashevskiy <aik at ozlabs.ru> wrote:
>>>
>>> On 10/07/2020 15:23, Oliver O'Halloran wrote:
>>>> There's an optimisation in the PE setup which skips performing DMA
>>>> setup for a PE if we only have bridges in a PE. The assumption being
>>>> that only "real" devices will DMA to system memory, which is probably
>>>> fair. However, if we start off with only bridge devices in a PE then
>>>> add a non-bridge device the new device won't be able to use DMA  because
>>>> we never configured it.
>>>>
>>>> Fix this (admittedly pretty weird) edge case by tracking whether we've done
>>>> the DMA setup for the PE or not. If a non-bridge device is added to the PE
>>>> (via rescan or hotplug, or whatever) we can set up DMA on demand.
>>>
>>> So hotplug does not work on powernv then, right? I thought you tested it
>>> a while ago, or this patch is the result of that attempt? If it is, then
>>
>> It mostly works. Just the really niche case of hot plugging a bridge,
>> then later on hot plugging a device into the same bus which wouldn't
>> work.
> 
> Do not you have to have a slot (which is a bridge) for hotplug in the
> first place, to hotplug the bridge?


As discussed elsewhere, I missed that it is a non bridge device on the
same bus with previously plugged bridge. Now it all makes sense and


Reviewed-by: Alexey Kardashevskiy <aik at ozlabs.ru>


-- 
Alexey