Re: [Intel-wired-lan] [PATCH iwl-net] ixgbevf: fix link speed reporting for Hyper-V E610 VFs

[Tony Nguyen <anthony.l.nguyen@intel.com>]

On 7/23/2026 7:51 AM, Tomasz Lichwala wrote:

...

> +/**
> + * ixgbevf_hv_read_links_e610 - read link status from PCI config space
> + * @hw: pointer to hardware structure
> + * @links_reg: pointer to store read value
> + *
> + * On Hyper-V E610 VFs the VFLINKS register does not carry valid link speed.
> + * Instead, link status is exposed through emulated PCI config space at offset
> + * 0x209 in VFLINKS register format.
> + *
> + * Return: 0 on success, negative error code on failure.
> + */
> +static s32 ixgbevf_hv_read_links_e610(struct ixgbe_hw *hw, u32 *links_reg)
> +{
> +	struct ixgbevf_adapter *adapter = hw->back;
> +
> +#if IS_ENABLED(CONFIG_PCI_MMCONFIG)
> +	u8 data[IXGBE_HV_LINK_STATUS_SIZE];
> +
> +	for (int i = 0; i < IXGBE_HV_LINK_STATUS_SIZE; i++) {
> +		int ret = pci_read_config_byte(adapter->pdev,
> +					       IXGBE_HV_LINK_STATUS_OFFSET + i,
> +					       &data[i]);
> +		if (ret)
> +			return pcibios_err_to_errno(ret);
> +	}
> +
> +	*links_reg = get_unaligned_le32(data);
> +	return 0;
> +#else
> +	dev_err_once(&adapter->pdev->dev, "cannot read link status, PCI_MMCONFIG is required for Hyper-V\n");
> +	return -EOPNOTSUPP;
> +#endif
> +}

I ran Sashiko locally on this and it reported the following:
Should a failed link read here return a fatal error to check_link, or
report link down and return 0?
When built without CONFIG_PCI_MMCONFIG this returns -EOPNOTSUPP on every
call, and it also returns an error on any persistent
pci_read_config_byte() failure.

>   /**
>    * ixgbevf_hv_check_mac_link_vf - check link
>    * @hw: pointer to private hardware struct
> @@ -909,6 +946,7 @@ static s32 ixgbevf_check_mac_link_vf(struct ixgbe_hw *hw,
>    * @autoneg_wait_to_complete: unused
>    *
>    * Hyper-V variant; there is no mailbox communication.
> + * For E610 VFs, link status is read from emulated PCI config space.
>    */
>   static s32 ixgbevf_hv_check_mac_link_vf(struct ixgbe_hw *hw,
>   					ixgbe_link_speed *speed,
> @@ -923,13 +961,32 @@ static s32 ixgbevf_hv_check_mac_link_vf(struct ixgbe_hw *hw,
>   	if (!mbx->ops.check_for_rst(hw) || !mbx->timeout)
>   		mac->get_link_status = true;
>   
> +	/* E610 VFs always read link status from emulated PCI config space
> +	 * because VFLINKS does not carry valid speed for these devices.
> +	 * Skip get_link_status caching since PCI config reads are cheap.
> +	 */
> +	if (mac->type == ixgbe_mac_e610_vf) {
> +		s32 ret = ixgbevf_hv_read_links_e610(hw, &links_reg);
> +
> +		if (ret) {
> +			*link_up = false;
> +			*speed = IXGBE_LINK_SPEED_UNKNOWN;
> +			return ret;
> +		}
> +		goto decode;
> +	}
> +
Can this cause a repeating reset loop on the degraded configuration?
The non-zero return propagates up through mac.ops.check_link() into
ixgbevf_watchdog_update_link():
     err = hw->mac.ops.check_link(hw, &link_speed, &link_up, false);
     ...
     if (err && time_after(jiffies, adapter->last_reset + (10 * HZ))) {
         set_bit(__IXGBEVF_RESET_REQUESTED, &adapter->state);
         link_up = false;
     }
A device reset cannot make CONFIG_PCI_MMCONFIG appear at compile time, nor
fix a persistent config-space read failure, so wouldn't every watchdog
cycle re-arm __IXGBEVF_RESET_REQUESTED roughly every 10 seconds, leaving
the interface permanently down and continuously resetting?
Before this patch the Hyper-V check_link callback always returned 0, so no
reset request was triggered. Would returning 0 with link_up=false and
speed IXGBE_LINK_SPEED_UNKNOWN for the unsupported/degraded case avoid the
loop?
One related note: the dev_err_once() reads as a benign one-time notice,
but the underlying -EOPNOTSUPP is returned on every poll and drives the
repeating reset behavior above.

Thanks,
Tony