Re: [Qemu-devel] [qemu-s390x] [RFC PATCH 1/3] hw/Kconfig: PCI bus implies PCI_DEVICES

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 7/15/19 3:19 PM, Thomas Huth wrote:
> On 15/07/2019 13.09, Cornelia Huck wrote:
>> On Mon, 15 Jul 2019 13:04:28 +0200
>> Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
>>
>>> On 7/15/19 12:56 PM, Cornelia Huck wrote:
>>>> On Mon, 15 Jul 2019 12:48:55 +0200
>>>> Thomas Huth <thuth@redhat.com> wrote:
>>>>   
>>>>> On 15/07/2019 12.19, Peter Maydell wrote:  
>>>>>> On Mon, 15 Jul 2019 at 11:15, Thomas Huth <thuth@redhat.com> wrote:    
>>>>>>>
>>>>>>> On 15/07/2019 11.55, Philippe Mathieu-Daudé wrote:    
>>>>>>>> If a controller device provides a PCI bus, we can plug any PCI
>>>>>>>> daughter card on it.
>>>>>>>>
>>>>>>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>>>>>> ---    
>>>>>>     
>>>>>>>> diff --git a/hw/pci/Kconfig b/hw/pci/Kconfig
>>>>>>>> index 77f8b005ff..0f7267db35 100644
>>>>>>>> --- a/hw/pci/Kconfig
>>>>>>>> +++ b/hw/pci/Kconfig
>>>>>>>> @@ -1,5 +1,6 @@
>>>>>>>>  config PCI
>>>>>>>>      bool
>>>>>>>> +    imply PCI_DEVICES    
>>>>>>>
>>>>>>> No, please don't change this. This was done on purpose, since almost all
>>>>>>> PCI_DEVICES do not work on s390x (so s390x does *not* imply PCI_DEVICES).    
>>>>>>
>>>>>> But that means that every board that provides PCI has to have an
>>>>>> "imply PCI_DEVICES" line, which is pretty clunky just to work
>>>>>> around an s390x limitation.
>>>>>>
>>>>>> Is there some way in the Kconfig syntax for s390x to say
>>>>>> "no PCI_DEVICES" so we can have the corner-case be handled
>>>>>> by the s390x Kconfig in one place rather than in 20 places
>>>>>> affecting everywhere except s390x?    
>>>>>
>>>>> IIRC the problem on s390x are the legacy IRQs. s390x has only MSIs. So I
>>>>> guess the correct way to fix this would be to introduce some
>>>>> PCI_LEGACY_IRQ switch and let all old devices that do not work with MSI
>>>>> depend on it.  
>>>>
>>>> s/MSI/MSI-X/, IIRC. Not sure how far 'legacy' would stretch.  
>>>
>>> Maybe we can have something like PCI_LEGACY_DEVICES and PCI_MSI_DEVICES?
>>>
>>> So if s390x only selects PCI_LEGACY (not PCI_MSI) bus, then it only get
>>> legacy devices?
>>
>> Wrong way around? We need MSI-X for s390x, not plain MSI or
>> 'legacy' (whatever that is).
> 
> With "legacy" I meant the old level-triggered interrupts from the early
> PCI (non-express) days. Sorry for being imprecise here.
> 
> So maybe we need two new switches, PCI_CLASSIC (or so) and PCI_MSIX, and
> then the PCI devices should be marked with "default y if PCI_CLASSIC" if
> they do not have MSIX support, and with "default y if PCI_MSIX" if they
> have MSI-X support?

Something like that :)

Per Wikipedia:

  Conventional PCI and PCI-X are sometimes called Parallel PCI
  in order to distinguish them technologically from their more
  recent successor PCI Express, which adopted a serial,
  lane-based architecture.

  The PCI-SIG introduced the serial PCI Express in c. 2004. At
  the same time, they renamed PCI as Conventional PCI.

  PCI Express does not have physical interrupt lines at all.
  It uses message-signaled interrupts exclusively.

What about PCI_CONVENTIONAL then?

Regards,

Phil.