Re: [Qemu-devel] [PATCH 1/4] hw/pcie: fix Extended Configuration Space for devices with no Extended Capabilities

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jan 04, 2017 at 09:57:15PM +0200, Marcel Apfelbaum wrote:
> Absence of any Extended Capabilities is required to be
> indicated by an Extended Capability header with a Capability ID of
> 0000h, a Capability Version of 0h, and a Next Capability Offset of 000h.
> 
> Instead of inserting a 'NULL' capability is simpler to mark the start
> of the Extended Configuration Space as read-only to achieve the same
> behaviour.
> 
> Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>

Kind of hacky and only theoretical - I don't think any guest writes
there - but ok. However I think
1. we should init config to 0 too
2. this needs a compat flag

> ---
>  hw/pci/pcie.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> index 99cfb45..62c1def 100644
> --- a/hw/pci/pcie.c
> +++ b/hw/pci/pcie.c
> @@ -109,6 +109,9 @@ int pcie_cap_init(PCIDevice *dev, uint8_t offset, uint8_t type, uint8_t port)
>                   PCI_EXP_DEVCAP2_EFF | PCI_EXP_DEVCAP2_EETLPP);
>  
>      pci_set_word(dev->wmask + pos + PCI_EXP_DEVCTL2, PCI_EXP_DEVCTL2_EETLPPB);
> +
> +    /* read-only to behave like a 'NULL' Extended Capability Header */
> +    pci_set_long(dev->wmask + PCI_CONFIG_SPACE_SIZE, 0);
>      return pos;
>  }
>  
> -- 
> 2.5.5