On Tue, Jan 20, 2026 at 05:04:53AM +0000, Russell King (Oracle) wrote:

On Mon, Jan 19, 2026 at 11:21:25AM -0800, Jakub Kicinski wrote:

quoted

This is an AI-generated review of your patch. The human sending this
email has considered the AI review valid, or at least plausible.

For local reproduction steps see https://netdev-ai.bots.linux.dev/ai-local.html
---
net: stmmac: add stmmac core serdes support

This commit adds SerDes PHY support to the stmmac core driver, moving it
from platform glue into the integrated PCS driver. The SerDes is managed
through phy_init/phy_exit for lifecycle and phy_power_on/phy_power_off
for the power state.

quoted

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_pcs.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_pcs.c
index 2f826fe7229b..4d1902f3a58f 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_pcs.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_pcs.c

[ ... ]

quoted

static int dwmac_integrated_pcs_enable(struct phylink_pcs *pcs)
{
	struct stmmac_pcs *spcs = phylink_pcs_to_stmmac_pcs(pcs);
+	struct stmmac_priv *priv = spcs->priv;
+	int ret;

-	stmmac_mac_irq_modify(spcs->priv, 0, spcs->int_mask);
+	ret = dwmac_serdes_power_on(priv);
+	if (ret)
+		return ret;
+
+	if (spcs->interface != PHY_INTERFACE_MODE_NA) {
+		ret = dwmac_serdes_set_mode(priv, spcs->interface);
+		if (ret)
+			return ret;

                        ^^^^^^^^^^

If dwmac_serdes_set_mode() fails here, doesn't this leave the SerDes in
a powered-on state? dwmac_serdes_power_on() succeeded at this point but
there's no corresponding dwmac_serdes_power_off() call before returning
the error.

Looking at phylink_major_config(), it appears to discard the return
value from phylink_pcs_enable(), so the caller won't know to call
pcs_disable() to clean up the power state.

This AI analysis is incorrect.

By the time phylink_pcs_enable() has been called, the PCS is already
plumbed in to phylink. It _will_ have phylink_pcs_disable() called on
it at some point in the future, either by having the PCS displaced
by another in a subsequent phylink_major_config(), or by a driver
calling phylink_stop().

If we clean up here, then we will call dwmac_serdes_power_off() twice.

Yes, it's not "nice" but that's the way phylink is right now, and
without reworking phylink to record that pcs_enable() has failed
to avoid a subsequent pcs_disable(), and to stop the major config
(which then potentially causes a whole bunch of other issues). I
don't even want to think about that horrid scenario at the moment.

More to the point, if dwmac_integrated_pcs_enable() fails at
dwmac_serdes_power_on() (thus, the SerDes is _not_ powered on), by your
own admission of this PCS calling convention, sooner or later
dwmac_integrated_pcs_disable() -> dwmac_serdes_power_off() will still be
called, leading to a negative phy->power_count.

That is to say, if the model is "irrespective of whether pcs_enable()
succeeds or fails mid way, pcs_disable is called anyway()", then these
methods are not prepared to handle that reliably.