[PATCH net v2 1/6] net: pcs: mtk-lynxi: check regmap reads in mtk_pcs_lynxi_get_state()

mtk_pcs_lynxi_get_state() ignores regmap_read()'s return value; a
failed read leaves bm and adv holding uninitialized stack values
which are then decoded into the reported link state. The regmaps
backing the MT7531 SGMII PCS instances sit on an MDIO bus where
reads can fail. Check both reads and report the link as down on
error; phylink presets state->link before the callback, so a bare
return would leave a failed read reported as link-up.

Fixes: 4765a9722e09 ("net: pcs: add driver for MediaTek SGMII PCS")
Signed-off-by: Daniel Golle <[email protected]>
Reviewed-by: Andrew Lunn <[email protected]>
---
v2:
 * set state->link = false on the failed-read path so a read error
   reports the link as down instead of leaving phylink's preset
   link-up (Sashiko AI review)

 drivers/net/pcs/pcs-mtk-lynxi.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/net/pcs/pcs-mtk-lynxi.c b/drivers/net/pcs/pcs-mtk-lynxi.c
index a753bd88cbc2..7290fc3e5d18 100644
--- a/drivers/net/pcs/pcs-mtk-lynxi.c
+++ b/drivers/net/pcs/pcs-mtk-lynxi.c
@@ -113,8 +113,11 @@ static void mtk_pcs_lynxi_get_state(struct phylink_pcs *pcs,
 	unsigned int bm, adv;
 
 	/* Read the BMSR and LPA */
-	regmap_read(mpcs->regmap, SGMSYS_PCS_CONTROL_1, &bm);
-	regmap_read(mpcs->regmap, SGMSYS_PCS_ADVERTISE, &adv);
+	if (regmap_read(mpcs->regmap, SGMSYS_PCS_CONTROL_1, &bm) ||
+	    regmap_read(mpcs->regmap, SGMSYS_PCS_ADVERTISE, &adv)) {
+		state->link = false;
+		return;
+	}
 
 	phylink_mii_c22_pcs_decode_state(state, neg_mode,
 					 FIELD_GET(SGMII_BMSR, bm),
-- 
2.55.0