Re: [PATCH net-next v8 2/6] net: pcs: xpcs: re-initiate clause 37 Auto-negotiation

["Russell King (Oracle)" <linux@armlinux.org.uk>]

On Wed, Feb 26, 2025 at 03:48:33PM +0800, Choong Yong Liang wrote:
> diff --git a/drivers/net/pcs/pcs-xpcs-wx.c b/drivers/net/pcs/pcs-xpcs-wx.c
> index fc52f7aa5f59..f73ab04d09f0 100644
> --- a/drivers/net/pcs/pcs-xpcs-wx.c
> +++ b/drivers/net/pcs/pcs-xpcs-wx.c
> @@ -172,11 +172,9 @@ int txgbe_xpcs_switch_mode(struct dw_xpcs *xpcs, phy_interface_t interface)
>  		return 0;
>  	}
>  
> -	if (xpcs->interface == interface && !txgbe_xpcs_mode_quirk(xpcs))
> +	if (!txgbe_xpcs_mode_quirk(xpcs))
>  		return 0;
>  
> -	xpcs->interface = interface;
> -

...

> --- a/drivers/net/pcs/pcs-xpcs.c
> +++ b/drivers/net/pcs/pcs-xpcs.c
> @@ -602,12 +602,37 @@ static void xpcs_get_interfaces(struct dw_xpcs *xpcs, unsigned long *interfaces)
>  		__set_bit(compat->interface, interfaces);
>  }
>  
> +static int xpcs_switch_interface_mode(struct dw_xpcs *xpcs,
> +				      phy_interface_t interface)
> +{
> +	int ret = 0;
> +
> +	if (xpcs->interface != interface) {
> +		if (xpcs->info.pma == WX_TXGBE_XPCS_PMA_10G_ID) {
> +			ret = txgbe_xpcs_switch_mode(xpcs, interface);
> +			if (ret)
> +				return ret;

The above modification changes the functionality.

In the old code, txgbe_xpcs_switch_mode() does its work when
xpcs->interface is not the same as interface OR txgbe_xpcs_mode_quirk()
is true.

Your replacement code calls txgbe_xpcs_switch_mode() when 
xpcs->interface is not the same as interface, *and* it can do its
work when txgbe_xpcs_mode_quirk() returns true.

So, e.g. when txgbe_xpcs_mode_quirk() returns false, but the interface
changes, txgbe_xpcs_mode_quirk() used to do its work, but as a result
if your changes, it becomes a no-op.

The point of txgbe_xpcs_mode_quirk() is to always do the work if it
returns true, even if the interface mode doesn't change.

Therefore, this patch is logically incorrect, and likely breaks TXGBE.

-- 
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