Re: [PATCH v5 06/13] hw/core/qdev: handle parent bus change regarding resettable

[Cornelia Huck]

On Fri, 29 Nov 2019 18:41:26 +0000
Peter Maydell <address@hidden> wrote:

> On Fri, 18 Oct 2019 at 16:07, Damien Hedde <address@hidden> wrote:
> >
> > In qdev_set_parent_bus(), when changing the parent bus of a
> > realized device, if the source and destination buses are not in the
> > same reset state, some adaptation are required. This patch adds  
> 
> "adaptations"
> 
> > needed call to resettable_change_parent() to make sure a device reset
> > state stays coherent with its parent bus.
> >
> > The addition is a no-op if:
> > 1. the device being parented is not realized.
> > 2. the device is realized, but both buses are not under reset.
> >
> > Case 2 means that as long as qdev_set_parent_bus() is called
> > during the machine realization procedure (which is before the
> > machine reset so nothing is in reset), it is a no op.
> >
> > There are 49 call sites of qdev_set_parent_bus(). All but one fall
> > into the no-op case:
> > + 28 calls related to virtio (in hw/{s390x,display,virtio}/
> >   {vhost,virtio}-xxx.c) to set a _vdev_/_vgpu_ composing device
> >   parent bus just before realizing the _vdev_/_vgpu_.
> > + hw/qdev.c: when creating a device in qdev_try_create()
> > + hw/sysbus.c: when initializing a device in the sysbus
> > + hw/display/virtio-gpu-pci.c: before realizing VirtIOGPUPCIBase/vgpu
> > + hw/display/virtio-vga.c: before realizing VirtIOVGABase/vgpu
> > + hw/i386/amd_iommu.c: before realizing AMDVIState/pci
> > + hw/misc/auxbus.c: when creating an AUXBus
> > + hw/misc/auxbus.c: when creating an AUXBus child
> > + hw/misc/macio/macio.c: when initializing a MACIOState child
> > + hw/misc/macio/macio.c: before realizing NewWorldMacIOState/pmu
> > + hw/misc/macio/macio.c: before realizing NewWorldMacIOState/cuda
> > + hw/pci-host/designware.c: before realizing DesignwarePCIEHost/root
> > + hw/pci-host/gpex.c: before realizing GPEXHost/root
> > + hw/pci-host/prep.c: when initializaing PREPPCIState/pci_dev
> > + hw/pci-host/q35.c: before realizing Q35PCIHost/mch
> > + hw/pci-host/versatile.c: when initializing PCIVPBState/pci_dev
> > + hw/pci-host/xilinx-pcie.c: before realizing XilinxPCIEHost/root
> > + hw/s390x/event-facility.c: when creating SCLPEventFacility/
> >                              TYPE_SCLP_QUIESCE
> > + hw/s390x/event-facility.c: ditto with SCLPEventFacility/
> >                              TYPE_SCLP_CPU_HOTPLUG
> > + hw/s390x/sclp.c: Not trivial because it is called on a SLCPDevice
> >   just after realizing it. Ok because at this point the destination
> >   bus (sysbus) is not in reset; the realize step is before the
> >   machine reset.
> > + hw/sd/core.c: Not OK. Used in sdbus_reparent_card(). See below.
> > + hw/ssi/ssi.c: Used to put spi slave on spi bus and connect the cs
> >   line in ssi_auto_connect_slave(). Ok because this function is only
> >   used in realize step in hw/ssi/aspeed_smc.ci, hw/ssi/imx_spi.c,
> >   hw/ssi/mss-spi.c, hw/ssi/xilinx_spi.c and hw/ssi/xilinx_spips.c.
> > + hw/xen/xen-legacy-backend.c: when creating a XenLegacyDevice device
> > + qdev-monitor.c: in device hotplug creation procedure before realize  
> 
> This is a really useful analysis to have in the commit message;
> thanks!
> 
> (Side note: I wonder if the sclp.c case could be reordered so
> it realizes the device after parenting it? Anyway, not something
> to worry about now.)

As far as I can see, that should work. This code is a bit weird anyway;
the problem is that we need the sysbus somewhere in there... I'm
wondering if that can be handled in a different way. But agreed, that
is something we can revisit later.

> 
> > Note that this commit alone will have no effect, right now there is no
> > use of resettable API to reset anything. So a bus will never be tagged
> > as in-reset by this same API.
> >
> > The one place where side-effect will occurs is in hw/sd/core.c in
> > sdbus_reparent_card(). This function is only used in the raspi machines,
> > including during the sysbus reset procedure. This case will be fixed by
> > a following commit before globally enabling resettable API for sysbus
> > reset.
> >
> > Signed-off-by: Damien Hedde <address@hidden>  
> 
> Reviewed-by: Peter Maydell <address@hidden>
> 
> thanks
> -- PMM
>