Re: [PATCH v6 net-next 11/15] net: dsa: netc: add phylink MAC operations

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Flawed read-modify-write logic in `netc_mac_port_rmw()` causes state desynchronization and clobbers PMAC registers.
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commit e2073763516dc99734e9f1436d4b8e960d8ce680
Author: Wei Fang <wei.fang@nxp.com>

    net: dsa: netc: add phylink MAC operations

This commit implements phylink MAC operations for NETC switch ports, including
capabilities retrieval and link configuration callbacks.

> diff --git a/drivers/net/dsa/netc/netc_main.c b/drivers/net/dsa/netc/netc_main.c
> index 8e3a3230226c3..8c1317b72a81d 100644
> --- a/drivers/net/dsa/netc/netc_main.c
> +++ b/drivers/net/dsa/netc/netc_main.c
[ ... ]
> @@ -43,6 +43,26 @@ static void netc_mac_port_wr(struct netc_port *np, u32 reg, u32 val)
>  		netc_port_wr(np, reg + NETC_PMAC_OFFSET, val);
>  }
>  
> +static void netc_mac_port_rmw(struct netc_port *np, u32 reg,
> +			      u32 mask, u32 val)
> +{
> +	u32 old, new;
> +
> +	if (is_netc_pseudo_port(np))
> +		return;
> +
> +	WARN_ON((mask | val) != mask);
> +
> +	old = netc_port_rd(np, reg);
> +	new = (old & ~mask) | val;
> +	if (new == old)
> +		return;
> +
> +	netc_port_wr(np, reg, new);
> +	if (np->caps.pmac)
> +		netc_port_wr(np, reg + NETC_PMAC_OFFSET, new);

Does this code lead to desynchronized state and clobbered PMAC registers?

Because old is read exclusively from the MAC 0 register, if new == old, the
function returns immediately. If the preemptable MAC 1 register had a
different state (e.g. from the bootloader), it would not be updated and could
remain permanently out of sync.

Additionally, if new != old, this writes the modified MAC 0 state to MAC 1.
Could this clobber any independent state in the MAC 1 register by overwriting
unmasked bits with MAC 0's values?

Would it be safer to perform independent read-modify-write cycles for each
MAC's register to preserve their respective unmasked bits?

> +}
> +

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Sashiko AI review · https://sashiko.dev/#/patchset/20260509102954.4116624-1-wei.fang@nxp.com?part=11