[PATCH net v2] r8152: Use BMSR to detect the link state

[Linmao Li]

r8152 detects carrier from PLA_PHYSTATUS without reading BMSR, so
BMSR_LSTATUS can still be latched low when the carrier comes up.
Since commit f6f2e946aa4d ("net: mii: Fix the Speed display when the
network cable is not connected"), the first speed query after link up
can then report SPEED_UNKNOWN, leaving NetworkManager at 0 Mb/s until
the next carrier change.

Use BMSR_LSTATUS in set_carrier() and rtl8152_runtime_resume(), so the
driver consumes the latched link down itself. If the first read still
reports link down, the next link-up notification triggers another read
and brings the carrier up.

Tested on an RTL8153B with a 6.6-based kernel. In 5 rebinds and 6 cable
replugs, the first read returned LSTATUS=0, a second link-up
notification came about 32 ms later, the second read returned
LSTATUS=1 and the carrier went up; NetworkManager reported 1000 Mb/s.
Runtime suspend/resume with the link up did not change the carrier.

Fixes: f6f2e946aa4d ("net: mii: Fix the Speed display when the network cable is not connected")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Linmao Li <lilinmao@xxxxxxxxxx>
---
v2:
- Fix it in r8152 instead of mii.c, detecting the link from BMSR as
  suggested by Andrew Lunn.
- Also use BMSR in rtl8152_runtime_resume().
v1: https://lore.kernel.org/netdev/20260930113842.2640928-1-lilinmao@xxxxxxxxxx/

Only tested on an RTL8153B, with a 6.6-based kernel; the changed lines
are the same in net/main. I could not check whether BMSR_LSTATUS is
reliable on the 2.5G/5G/10G chips handled by this driver.
I could not reproduce a link drop that recovers while the device is
runtime suspended, so that case is only covered by code inspection.

r8152_mdio_read() cannot fail today. The pending RTL8157/RTL8159
series makes it return errors, so these two callers will need error
handling once that is merged.

 drivers/net/usb/r8152.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
index f61686433031..e3947eb796c5 100644
--- a/drivers/net/usb/r8152.c
+++ b/drivers/net/usb/r8152.c
@@ -6979,11 +6979,8 @@ static void set_carrier(struct r8152 *tp)
 {
 	struct net_device *netdev = tp->netdev;
 	struct napi_struct *napi = &tp->napi;
-	u16 speed;
-
-	speed = rtl8152_get_speed(tp);
 
-	if (speed & LINK_STATUS) {
+	if (r8152_mdio_read(tp, MII_BMSR) & BMSR_LSTATUS) {
 		if (!netif_carrier_ok(netdev)) {
 			tp->rtl_ops.enable(tp);
 			netif_stop_queue(netdev);
@@ -8653,7 +8650,7 @@ static int rtl8152_runtime_resume(struct r8152 *tp)
 		set_bit(WORK_ENABLE, &tp->flags);
 
 		if (netif_carrier_ok(netdev)) {
-			if (rtl8152_get_speed(tp) & LINK_STATUS) {
+			if (r8152_mdio_read(tp, MII_BMSR) & BMSR_LSTATUS) {
 				rtl_start_rx(tp);
 			} else {
 				netif_carrier_off(netdev);
-- 
2.25.1