Re: [Qemu-devel] [RFC 1/4] spapr_pci: Delegate placement of PCI host bridges to machine type

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Oct 06, 2016 at 09:10:41AM +0200, Laurent Vivier wrote:
> 
> 
> On 06/10/2016 05:03, David Gibson wrote:
> > The 'spapr-pci-host-bridge' represents the virtual PCI host bridge (PHB)
> > for a PAPR guest.  Unlike on x86, it's routine on Power (both bare metal
> > and PAPR guests) to have numerous independent PHBs, each controlling a
> > separate PCI domain.
> > 
> > There are two ways of configuring the spapr-pci-host-bridge device: first
> > it can be done fully manually, specifying the locations and sizes of all
> > the IO windows.  This gives the most control, but is very awkward with 6
> > mandatory parameters.  Alternatively just an "index" can be specified
> > which essentially selects from an array of predefined PHB locations.
> > The PHB at index 0 is automatically created as the default PHB.
> > 
> > The current set of default locations causes some problems for guests with
> > large RAM (> 1 TiB) or PCI devices with very large BARs (e.g. big nVidia
> > GPGPU cards via VFIO).  Obviously, for migration we can only change the
> > locations on a new machine type, however.
> > 
> > This is awkward, because the placement is currently decided within the
> > spapr-pci-host-bridge code, so it breaks abstraction to look inside the
> > machine type version.
> > 
> > So, this patch delegates the "default mode" PHB placement from the
> > spapr-pci-host-bridge device back to the machine type via a public method
> > in sPAPRMachineClass.  It's still a bit ugly, but it's about the best we
> > can do.
> > 
> > For now, this just changes where the calculation is done.  It doesn't
> > change the actual location of the host bridges, or any other behaviour.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  hw/ppc/spapr.c              | 34 ++++++++++++++++++++++++++++++++++
> >  hw/ppc/spapr_pci.c          | 22 ++++++++--------------
> >  include/hw/pci-host/spapr.h | 11 +----------
> >  include/hw/ppc/spapr.h      |  4 ++++
> >  4 files changed, 47 insertions(+), 24 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 03e3803..f6e9c2a 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -2370,6 +2370,39 @@ static HotpluggableCPUList *spapr_query_hotpluggable_cpus(MachineState *machine)
> >      return head;
> >  }
> >  
> > +static void spapr_phb_placement(sPAPRMachineState *spapr, uint32_t index,
> > +                                uint64_t *buid, hwaddr *pio, hwaddr *pio_size,
> > +                                hwaddr *mmio, hwaddr *mmio_size,
> > +                                unsigned n_dma, uint32_t *liobns, Error **errp)
> > +{
> > +    const uint64_t base_buid = 0x800000020000000ULL;
> > +    const hwaddr phb0_base = 0x10000000000ULL; /* 1 TiB */
> > +    const hwaddr phb_spacing = 0x1000000000ULL; /* 64 GiB */
> > +    const hwaddr mmio_offset = 0xa0000000; /* 2 GiB + 512 MiB */
> > +    const hwaddr pio_offset = 0x80000000; /* 2 GiB */
> > +    const uint32_t max_index = 255;
> 
> Why do you use new "const" instead of already defined "#define" from
> spapr.h?

Because the point of this change is that all the knowledge about where
the PHBis placed is supposed to be restrictedto this function.  Making
these local consts enforces that.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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