[SeaBIOS] [PATCH V2] fw/pci: do not automatically allocate IO region for PCIe bridges

[Michael S. Tsirkin]

On Mon, Dec 07, 2015 at 02:05:14PM +0200, Marcel Apfelbaum wrote:
> PCIe downstream ports (Root Ports and switches Downstream Ports) appear
> to firmware as PCI-PCI bridges and a 4K IO space is allocated for them
> even if there is no device behind them requesting IO space,
> all that for hotplug purpose.
> 
> However, PCIe devices can work without IO, so there is no need
> to allocate IO space for hotplug.
> 
> Signed-off-by: Marcel Apfelbaum <marcel at redhat.com>

Acked-by: Michael S. Tsirkin <mst at redhat.com>


> ---
> v1 -> v2:
>  - Addressed Gerd's comments:
>     - move pci_find_capability out of the loop and call it only once.
>     - more descriptive names for variables 
> 
> Notes:
>  - This patch fixes a 15 PCIe Root ports limitation when used with
>    virtio pci-express devices having no IO space requirements:
>       <qemu cmd line> -M q35 `for i in {1..15}; do echo -device ioh3420,chassis=$i,id=b$i -device virtio-net-pci,bus=b$i,disable-legacy=on; done`
>  - There is a patch on QEMU devel list that tackles the problem from another angle
>    by allowing PCIe downstream ports to not forward IO requests.
>        https://lists.gnu.org/archive/html/qemu-devel/2015-11/msg04478.html
>  - The mentioned patch is of course not enough and also requires management software intervention.
> 
> Thanks,
> Marcel
> 
>  src/fw/pciinit.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
> index 7b8aab7..c31c2fa 100644
> --- a/src/fw/pciinit.c
> +++ b/src/fw/pciinit.c
> @@ -645,9 +645,8 @@ pci_region_create_entry(struct pci_bus *bus, struct pci_device *dev,
>      return entry;
>  }
>  
> -static int pci_bus_hotplug_support(struct pci_bus *bus)
> +static int pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
>  {
> -    u8 pcie_cap = pci_find_capability(bus->bus_dev, PCI_CAP_ID_EXP, 0);
>      u8 shpc_cap;
>  
>      if (pcie_cap) {
> @@ -727,7 +726,8 @@ static int pci_bios_check_devices(struct pci_bus *busses)
>               */
>              parent = &busses[0];
>          int type;
> -        int hotplug_support = pci_bus_hotplug_support(s);
> +        u8 pcie_cap = pci_find_capability(s->bus_dev, PCI_CAP_ID_EXP, 0);
> +        int hotplug_support = pci_bus_hotplug_support(s, pcie_cap);
>          for (type = 0; type < PCI_REGION_TYPE_COUNT; type++) {
>              u64 align = (type == PCI_REGION_TYPE_IO) ?
>                  PCI_BRIDGE_IO_MIN : PCI_BRIDGE_MEM_MIN;
> @@ -736,7 +736,8 @@ static int pci_bios_check_devices(struct pci_bus *busses)
>              if (pci_region_align(&s->r[type]) > align)
>                   align = pci_region_align(&s->r[type]);
>              u64 sum = pci_region_sum(&s->r[type]);
> -            if (!sum && hotplug_support)
> +            int resource_optional = pcie_cap && (type == PCI_REGION_TYPE_IO);
> +            if (!sum && hotplug_support && !resource_optional)
>                  sum = align; /* reserve min size for hot-plug */
>              u64 size = ALIGN(sum, align);
>              int is64 = pci_bios_bridge_region_is64(&s->r[type],
> -- 
> 2.1.0