[PATCH net 2/2] amd-xgbe: fix an_irq leak causing permanent -EBUSY on PHY (re)start

[Stepan Svatenko <ssvatenko@iit.org.ua>]

xgbe_phy_start() requests the separate AN/PCS interrupt (an_irq) and,
on any failure past that point, is expected to free it again via the
err_irq/err_stop labels before returning an error. The last error path
skips that cleanup:

  pdata->phy_started = 1;
  xgbe_an_init(pdata);
  xgbe_an_enable_interrupts(pdata);
  return xgbe_phy_config_aneg(pdata);   <- returns directly on error

xgbe_phy_config_aneg() (via __xgbe_phy_config_aneg()) can genuinely
fail, e.g. when phy_impl.an_config() fails against a non-functional
SFP module. When it does, xgbe_phy_start() returns that error without
going through err_irq/err_stop, so:

 - an_irq is never freed with devm_free_irq(), and
 - pdata->phy_started is left set to 1, even though the caller
   (xgbe_start()) now treats this as a failed start and does not call
   phy_if->phy_stop() itself on that path.

Any later retry of xgbe_phy_start() (interface bring-up retried by
userspace, or the driver's own recovery logic) then calls
devm_request_irq() for the same still-registered an_irq and gets
-EBUSY every time, with no way to recover short of a reboot/power
cycle:

  genirq: Flags mismatch irq 63. 00200000 (enp8s0f3-pcs) vs. 00200000 (enp8s0f3-pcs)
  amd-xgbe 0000:08:00.3: error -EBUSY: request_irq(63) xgbe_an_isr [amd_xgbe] 0x0 enp8s0f3-pcs
  amd-xgbe 0000:08:00.3 enp8s0f3: phy irq request failed

Reproduced on a SolidRun Bedrock V3000 (AMD Ryzen Embedded V3C48) by
inserting a non-functional SFP module, then bringing the interface up.

Fix this by routing the xgbe_phy_config_aneg() failure through
xgbe_phy_stop(), which already contains the correct, symmetric
teardown (disables AN, frees an_irq if separate, cancels the bh work,
stops the PHY implementation) and is safe to call here because it is
gated on pdata->phy_started.

Fixes: 7c12aa08779c ("amd-xgbe: Move the PHY support into amd-xgbe")
Cc: stable@vger.kernel.org
Signed-off-by: Stepan Svatenko <ssvatenko@iit.org.ua>
Assisted-by: Claude Code:claude-sonnet-5 [Bash] [Read] [Edit]
---
 drivers/net/ethernet/amd/xgbe/xgbe-mdio.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c b/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c
index 12770af031eb..638c24b9c83c 100644
--- a/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c
+++ b/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c
@@ -1445,7 +1445,19 @@ static int xgbe_phy_start(struct xgbe_prv_data *pdata)
 	xgbe_an_init(pdata);
 	xgbe_an_enable_interrupts(pdata);
 
-	return xgbe_phy_config_aneg(pdata);
+	ret = xgbe_phy_config_aneg(pdata);
+	if (ret) {
+		/* Tear down what was just brought up above (including
+		 * freeing the an_irq) instead of returning with phy_started
+		 * left set and an_irq still registered - otherwise a retry
+		 * calls devm_request_irq() on an already-owned an_irq and
+		 * gets stuck in a permanent -EBUSY loop.
+		 */
+		xgbe_phy_stop(pdata);
+		return ret;
+	}
+
+	return 0;
 
 err_irq:
 	if (pdata->dev_irq != pdata->an_irq)
-- 
2.55.0