Re: [SeaBIOS] [RFC PATCH v2 4/4] pci: enable RedHat PCI bridges to reserve additional buses on PCI init

[Alexander Bezzubikov]

By the way, any ideas on how to avoid 'bus overstealing' would
be greatly appreciated.
Static BIOS variable isn't applicable since its value isn't saved across
reboots.

2017-07-23 19:43 GMT+03:00 Alexander Bezzubikov :
> 2017-07-23 5:49 GMT+03:00 Michael S. Tsirkin :
> > On Sun, Jul 23, 2017 at 01:11:50AM +0300, Aleksandr Bezzubikov wrote:
> > > In case of Red Hat PCI bridges reserve additional buses, which number
> >
> > is provided
> > > in a vendor-specific capability.
> > > Signed-off-by: Aleksandr Bezzubikov
> > >
> > > src/fw/pciinit.c | 14 ++++++++++++--
> > >  1 file changed, 12 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
> > > index 864954f..f05a8b9 100644
> > > --- a/src/fw/pciinit.c
> > > +++ b/src/fw/pciinit.c
> > > @@ -15,6 +15,7 @@
> > >  #include "hw/pcidevice.h" // pci_probe_devices
> > >  #include "hw/pci_ids.h" // PCI_VENDOR_ID_INTEL
> > >  #include "hw/pci_regs.h" // PCI_COMMAND
> > > +#include "hw/pci_cap.h" // qemu_pci_cap
> > >  #include "list.h" // struct hlist_node
> > >  #include "malloc.h" // free
> > >  #include "output.h" // dprintf
> > > @@ -578,9 +579,18 @@ pci_bios_init_bus_rec(int bus, u8 *pci_bus)
> > >          pci_bios_init_bus_rec(secbus, pci_bus);
> > >      if (subbus != *pci_bus) {
> > >        u8 res_bus = 0;
> > >        if (pci_config_readw(bdf, PCI_VENDOR_ID) ==
> >
> > PCI_VENDOR_ID_REDHAT) {
> >
> > Check device ID as well.
>
> Not sure what ID/IDs we want to see here exactly. Now it can be
> only pcie-root-port (0xC then), but
> > >            u8 cap = pci_find_capability(bdf, PCI_CAP_ID_VNDR, 0);
> >
> > There could be multiple vendor capabilities. You want to scan them all.
> > >            if (cap) {
> > >                res_bus = pci_config_readb(bdf,
> > >                        cap + offsetof(struct
> >
> > redhat_pci_bridge_cap,
> > >                                       bus_res));
> >
> > You might want to add sanity checks e.g. overflow, and capability
> > length.
> >
> > Also, if all you use is offsetof, don't bother with a struct, just
> > add some defines.
>
> OK, will move this to defines.
> > >            }
> > >        }
> > >        dprintf(1, "PCI: subordinate bus = 0x%x -> 0x%x\n",
> > >                subbus, *pci_bus);
> > >        subbus = *pci_bus;
> > >                subbus, *pci_bus + res_bus);
> > >        subbus = *pci_bus + res_bus;
> >
> > So you take all present devices and add reserved ones - is that it?
> > If so it looks like this will steal extra buses each time you
> > add a child bus and reboot.
>
> You're right, such problem persists. Will think on what can be done here.
> > >      } else {
> > >          dprintf(1, "PCI: subordinate bus = 0x%x\n", subbus);
> > >      }