Re: [PATCH v4 1/7] hw/arm/smmu-common: Check SMMU has PCIe Root Complex association

[Jonathan Cameron via <qemu-devel@nongnu.org>]

On Thu, 19 Jun 2025 10:38:02 +0100
Jonathan Cameron <Jonathan.Cameron@huawei.com> wrote:

> On Thu, 19 Jun 2025 10:30:28 +0100
> Jonathan Cameron <Jonathan.Cameron@huawei.com> wrote:
> 
> > On Thu, 19 Jun 2025 09:05:07 +0100
> > Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com> wrote:
> >   
> > > > -----Original Message-----
> > > > From: Eric Auger <eric.auger@redhat.com>
> > > > Sent: Thursday, June 19, 2025 8:41 AM
> > > > To: Shameerali Kolothum Thodi
> > > > <shameerali.kolothum.thodi@huawei.com>; Jonathan Cameron
> > > > <jonathan.cameron@huawei.com>
> > > > Cc: Linuxarm <linuxarm@huawei.com>; qemu-arm@nongnu.org; qemu-
> > > > devel@nongnu.org; peter.maydell@linaro.org; jgg@nvidia.com;
> > > > nicolinc@nvidia.com; ddutile@redhat.com; berrange@redhat.com;
> > > > imammedo@redhat.com; nathanc@nvidia.com; mochs@nvidia.com;
> > > > smostafa@google.com; Wangzhou (B) <wangzhou1@hisilicon.com>;
> > > > jiangkunkun <jiangkunkun@huawei.com>; zhangfei.gao@linaro.org
> > > > Subject: Re: [PATCH v4 1/7] hw/arm/smmu-common: Check SMMU has PCIe
> > > > Root Complex association
> > > > 
> > > > Hi Shameer,
> > > > 
> > > > On 6/19/25 9:24 AM, Shameerali Kolothum Thodi wrote:      
> > > > > Hi Eric,
> > > > >      
> > > > >> -----Original Message-----
> > > > >> From: Eric Auger <eric.auger@redhat.com>
> > > > >> Sent: Wednesday, June 18, 2025 6:00 PM
> > > > >> To: Shameerali Kolothum Thodi
> > > > >> <shameerali.kolothum.thodi@huawei.com>; Jonathan Cameron
> > > > >> <jonathan.cameron@huawei.com>
> > > > >> Cc: Linuxarm <linuxarm@huawei.com>; qemu-arm@nongnu.org; qemu-
> > > > >> devel@nongnu.org; peter.maydell@linaro.org; jgg@nvidia.com;
> > > > >> nicolinc@nvidia.com; ddutile@redhat.com; berrange@redhat.com;
> > > > >> imammedo@redhat.com; nathanc@nvidia.com; mochs@nvidia.com;
> > > > >> smostafa@google.com; Wangzhou (B) <wangzhou1@hisilicon.com>;
> > > > >> jiangkunkun <jiangkunkun@huawei.com>; zhangfei.gao@linaro.org
> > > > >> Subject: Re: [PATCH v4 1/7] hw/arm/smmu-common: Check SMMU has      
> > > > PCIe      
> > > > >> Root Complex association
> > > > >>
> > > > >> Hi Shameer, Jonathan,
> > > > >>
> > > > >> On 6/18/25 10:35 AM, Shameerali Kolothum Thodi wrote:      
> > > > >>>> -----Original Message-----
> > > > >>>> From: Jonathan Cameron <jonathan.cameron@huawei.com>
> > > > >>>> Sent: Tuesday, June 17, 2025 5:53 PM
> > > > >>>> To: Eric Auger <eric.auger@redhat.com>
> > > > >>>> Cc: Shameerali Kolothum Thodi
> > > > >>>> <shameerali.kolothum.thodi@huawei.com>; Linuxarm
> > > > >>>> <linuxarm@huawei.com>; qemu-arm@nongnu.org; qemu-
> > > > >>>> devel@nongnu.org; peter.maydell@linaro.org; jgg@nvidia.com;
> > > > >>>> nicolinc@nvidia.com; ddutile@redhat.com; berrange@redhat.com;
> > > > >>>> imammedo@redhat.com; nathanc@nvidia.com; mochs@nvidia.com;
> > > > >>>> smostafa@google.com; Wangzhou (B) <wangzhou1@hisilicon.com>;
> > > > >>>> jiangkunkun <jiangkunkun@huawei.com>; zhangfei.gao@linaro.org
> > > > >>>> Subject: Re: [PATCH v4 1/7] hw/arm/smmu-common: Check SMMU has      
> > > > >> PCIe      
> > > > >>>> Root Complex association
> > > > >>>>
> > > > >>>> On Tue, 17 Jun 2025 09:49:54 +0200
> > > > >>>> Eric Auger <eric.auger@redhat.com> wrote:
> > > > >>>>      
> > > > >>>>> On 6/16/25 12:20 PM, Jonathan Cameron wrote:      
> > > > >>>>>> On Fri, 13 Jun 2025 15:44:43 +0100
> > > > >>>>>> Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>      
> > > > wrote:      
> > > > >>>>>>      
> > > > >>>>>>> Although this change does not affect functionality at present, it is      
> > > > >>>>>> Patch title says PCIe.  This check is vs PCI host bridge.
> > > > >>>>>>
> > > > >>>>>> No idea which one you wanted, but if it is PCIe needs to be
> > > > >>>>>> TYPC_PCIE_HOST_BRIDGE from pcie_host.h not the pci_host.h one
> > > > >>>>>> I think.      
> > > > >>>>> I think we need TYPE_PCI_HOST_BRIDGE as we want to check against      
> > > > >> pxb      
> > > > >>>>> pci-bridge/pci_expander_bridge.c:    .parent        =      
> > > > >>>> TYPE_PCI_HOST_BRIDGE,      
> > > > >> sorry but I still fail to understand why we can't just check against
> > > > >>
> > > > >> TYPE_PCI_HOST_BRIDGE for making sure the SMMU is attached to PXB or
> > > > >> GPEX. What does it fail to check? Why shall we care about PCI vs PCIe?      
> > > > > I think the concern is  getting any other TYPE_PCI_HOST_BRIDGE types      
> > > > attached      
> > > > > to SMMUv3 other than pxb-pcie or GPEX. For example you could do,
> > > > >
> > > > > -device pxb-cxl,bus_nr=12,bus=pcie.0,id=cxl.1 \
> > > > > -device arm-smmuv3,primary-bus=cxl.1,id=smmuv3.1 \
> > > > >
> > > > > as pxb-cxl is of type TYPE_PCI_HOST_BRIDGE. I don't know if there are any      
> > > > other      
> > > > > ones similar to this out there.
> > > > >
> > > > > So the aim is to make the checking more specific to PXB.      
> > > > 
> > > > thank you for the clarification. Is it invalid to have the SMMU
> > > > protecting RIDs comming from the pxb-cxl hierarchy?      
> > > 
> > > That’s a good question. I don't know that for sure.    
> > 
> > It should be fine to support CXL for this but we can work that out later.
> > 
> > For now limited use cases as there is no CXL VFIO support and the only thing
> > emulated devices do that the SMMU might influence is MSIX.
> > 
> > The one that concerned me is pxb-pci if we only care about pcie.
> > I'm not sure if we need to make that distinction or not.  
> >   
> Hmm. Shameer pointed out I hallucinated the existence of a PCI only expander bridge.
> So ignore that.
After some more discussions... 

Ah but it does - just called "pxb" - but it's irrelevant anyway as you can only add
them to a PCI root bridge (Shameer tested with a PCIe to PCI bridge with a pxb below
it and it rejects that config).  So can't plug them into virt anyway.

That's just for the record if I forget the whole discussion in future ;)

Jonathan

> 
> > Jonathan
> >   
> > > Anyway currently the full support for CXL on virt is in progress here,
> > > https://lore.kernel.org/qemu-devel/20250612134338.1871023-1-Jonathan.Cameron@huawei.com/
> > > 
> > > Jonathan?
> > > 
> > > Thanks,
> > > Shameer
> > >     
> > > >       
> > >     
> >   
>