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

From: "Philippe Mathieu-Daudé" <philmd@redhat.com>
To: Cornelia Huck <cohuck@redhat.com>, Thomas Huth <thuth@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>,
	Collin Walling <walling@linux.ibm.com>,
	"open list:RISC-V" <qemu-riscv@nongnu.org>,
	Eduardo Habkost <ehabkost@redhat.com>,
	Sagar Karandikar <sagark@eecs.berkeley.edu>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Helge Deller <deller@gmx.de>, Palmer Dabbelt <palmer@sifive.com>,
	Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>,
	QEMU Developers <qemu-devel@nongnu.org>,
	Aurelien Jarno <aurelien@aurel32.net>,
	"open list:S390" <qemu-s390x@nongnu.org>,
	qemu-arm <qemu-arm@nongnu.org>, qemu-ppc <qemu-ppc@nongnu.org>,
	Gerd Hoffmann <kraxel@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Alistair Francis <Alistair.Francis@wdc.com>,
	Richard Henderson <rth@twiddle.net>,
	Artyom Tarasenko <atar4qemu@gmail.com>,
	David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [Qemu-devel] [qemu-s390x] [RFC PATCH 1/3] hw/Kconfig: PCI bus implies PCI_DEVICES
Date: Mon, 15 Jul 2019 13:04:28 +0200	[thread overview]
Message-ID: <c1c68faf-0424-6c7c-e39f-42159457c3ee@redhat.com> (raw)
In-Reply-To: <20190715125653.6e65d575.cohuck@redhat.com>

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?

Other MSI compliant should select PCI_MSI instead. PCI alone seems to
give troubles.

> cc:ing Collin in case there's something else.
> 