On 05/28/21 01:06, Haozhong Zhang wrote:
> The current implementation leaves 0 in the maximum link width (MLW)
> and speed (MLS) fields of the PCI_EXP_LNKCAP register of a xio3130
> downstream port device. As a consequence, when that downstream port
> negotiates the link width and speed with its downstream device, 0 will
> be used and filled in the MLW and MLS fields of the PCI_EXP_LNKSTA
> register of that downstream port.
> 
> Normally, such 0 MLS and MLW in PCI_EXP_LNKSTA register only make the
> guest lspci output looks weird (like "speed unknown" and "x0 width").
> However, it also fails the hot-plug of device to the xio3130
> downstream port. The guest Linux kernel complains:
> 
>     pcieport 0000:01:00.0: pciehp: Slot(0): Cannot train link: status 0x2000
> 
> because the pciehp_hpc driver expects a read of valid (non-zero) MLW
> from PCI_EXP_LNKSTA register of that downstream port.
> 
> This patch addresses the above issue by setting MLW and MLS in
> PCI_EXP_LNKCAP of the xio3130 downstream port to values defined in its
> data manual, i.e., x1 and 2.5 GT respectively.
> 
> Signed-off-by: Haozhong Zhang <zhanghaozhong@bytedance.com>
> ---
>  hw/pci-bridge/xio3130_downstream.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/hw/pci-bridge/xio3130_downstream.c b/hw/pci-bridge/xio3130_downstream.c
> index 04aae72cd6..fbf9868ad7 100644
> --- a/hw/pci-bridge/xio3130_downstream.c
> +++ b/hw/pci-bridge/xio3130_downstream.c
> @@ -87,6 +87,13 @@ static void xio3130_downstream_realize(PCIDevice *d, Error **errp)
>          goto err_bridge;
>      }
>  
> +    /*
> +     * Following two fields must be set before calling pcie_cap_init() which
> +     * will fill them to MLS and MLW of PCI_EXP_LNKCAP register.
> +     */
> +    s->speed = QEMU_PCI_EXP_LNK_2_5GT;
> +    s->width = QEMU_PCI_EXP_LNK_X1;
> +
>      rc = pcie_cap_init(d, XIO3130_EXP_OFFSET, PCI_EXP_TYPE_DOWNSTREAM,
>                         p->port, errp);
>      if (rc < 0) {
> -- 
> 2.31.1
> 
>

Forgot to cc Marcel