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

From: Cornelia Huck <cohuck@redhat.com>
To: "Philippe Mathieu-Daudé" <philmd@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>,
	Collin Walling <walling@linux.ibm.com>,
	Sagar Karandikar <sagark@eecs.berkeley.edu>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Palmer Dabbelt <palmer@sifive.com>,
	Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>,
	QEMU Developers <qemu-devel@nongnu.org>,
	Alistair Francis <Alistair.Francis@wdc.com>,
	Gerd Hoffmann <kraxel@redhat.com>, Helge Deller <deller@gmx.de>,
	David Gibson <david@gibson.dropbear.id.au>,
	Artyom Tarasenko <atar4qemu@gmail.com>,
	Thomas Huth <thuth@redhat.com>,
	Eduardo Habkost <ehabkost@redhat.com>,
	"open list:S390" <qemu-s390x@nongnu.org>,
	qemu-arm <qemu-arm@nongnu.org>,
	Richard Henderson <rth@twiddle.net>,
	"open list:RISC-V" <qemu-riscv@nongnu.org>,
	qemu-ppc <qemu-ppc@nongnu.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Aurelien Jarno <aurelien@aurel32.net>
Subject: Re: [Qemu-devel] [qemu-s390x] [RFC PATCH 1/3] hw/Kconfig: PCI bus implies PCI_DEVICES
Date: Mon, 15 Jul 2019 13:09:55 +0200	[thread overview]
Message-ID: <20190715130955.4a117388.cohuck@redhat.com> (raw)
In-Reply-To: <c1c68faf-0424-6c7c-e39f-42159457c3ee@redhat.com>

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).

> 
> Other MSI compliant should select PCI_MSI instead. PCI alone seems to
> give troubles.
> 
> > cc:ing Collin in case there's something else.
> >   