net: usb: Correct PHY handling of smsc95xx

The smsc95xx driver is dropping phy speed settings and causing a stack
trace at device unbind:

[  536.379147] smsc95xx 2-1:1.0 eth1: unregister 'smsc95xx' usb-ci_hdrc.2-1, smsc95xx USB 2.0 Ethernet
[  536.425029] ------------[ cut here ]------------
[  536.429650] WARNING: CPU: 0 PID: 439 at fs/kernfs/dir.c:1535 kernfs_remove_by_name_ns+0xb8/0xc0
[  536.438416] kernfs: can not remove 'attached_dev', no directory
[  536.444363] Modules linked in: xts dm_crypt dm_mod atmel_mxt_ts smsc95xx usbnet
[  536.451748] CPU: 0 PID: 439 Comm: sh Tainted: G        W         5.15.0 #1
[  536.458636] Hardware name: Freescale i.MX53 (Device Tree Support)
[  536.464735] Backtrace: 
[  536.467190] [<80b1c904>] (dump_backtrace) from [<80b1cb48>] (show_stack+0x20/0x24)
[  536.474787]  r7:000005ff r6:8035b294 r5:600f0013 r4:80d8af78
[  536.480449] [<80b1cb28>] (show_stack) from [<80b1f764>] (dump_stack_lvl+0x48/0x54)
[  536.488035] [<80b1f71c>] (dump_stack_lvl) from [<80b1f788>] (dump_stack+0x18/0x1c)
[  536.495620]  r5:00000009 r4:80d9b820
[  536.499198] [<80b1f770>] (dump_stack) from [<80124fac>] (__warn+0xfc/0x114)
[  536.506187] [<80124eb0>] (__warn) from [<80b1d21c>] (warn_slowpath_fmt+0xa8/0xdc)
[  536.513688]  r7:000005ff r6:80d9b820 r5:80d9b8e0 r4:83744000
[  536.519349] [<80b1d178>] (warn_slowpath_fmt) from [<8035b294>] (kernfs_remove_by_name_ns+0xb8/0xc0)
[  536.528416]  r9:00000001 r8:00000000 r7:824926dc r6:00000000 r5:80df6c2c r4:00000000
[  536.536162] [<8035b1dc>] (kernfs_remove_by_name_ns) from [<80b1f56c>] (sysfs_remove_link+0x4c/0x50)
[  536.545225]  r6:7f00f02c r5:80df6c2c r4:83306400
[  536.549845] [<80b1f520>] (sysfs_remove_link) from [<806f9c8c>] (phy_detach+0xfc/0x11c)
[  536.557780]  r5:82492000 r4:83306400
[  536.561359] [<806f9b90>] (phy_detach) from [<806f9cf8>] (phy_disconnect+0x4c/0x58)
[  536.568943]  r7:824926dc r6:7f00f02c r5:82492580 r4:83306400
[  536.574604] [<806f9cac>] (phy_disconnect) from [<7f00a310>] (smsc95xx_disconnect_phy+0x30/0x38 [smsc95xx])
[  536.584290]  r5:82492580 r4:82492580
[  536.587868] [<7f00a2e0>] (smsc95xx_disconnect_phy [smsc95xx]) from [<7f001570>] (usbnet_stop+0x70/0x1a0 [usbnet])
[  536.598161]  r5:82492580 r4:82492000
[  536.601740] [<7f001500>] (usbnet_stop [usbnet]) from [<808baa70>] (__dev_close_many+0xb4/0x12c)
[  536.610466]  r8:83744000 r7:00000000 r6:83744000 r5:83745b74 r4:82492000
[  536.617170] [<808ba9bc>] (__dev_close_many) from [<808bab78>] (dev_close_many+0x90/0x120)
[  536.625365]  r7:00000001 r6:83745b74 r5:83745b8c r4:82492000
[  536.631026] [<808baae8>] (dev_close_many) from [<808bf408>] (unregister_netdevice_many+0x15c/0x704)
[  536.640094]  r9:00000001 r8:81130b98 r7:83745b74 r6:83745bc4 r5:83745b8c r4:82492000
[  536.647840] [<808bf2ac>] (unregister_netdevice_many) from [<808bfa50>] (unregister_netdevice_queue+0xa0/0xe8)
[  536.657775]  r10:8112bcc0 r9:83306c00 r8:83306c80 r7:8291e420 r6:83744000 r5:00000000
[  536.665608]  r4:82492000
[  536.668143] [<808bf9b0>] (unregister_netdevice_queue) from [<808bfac0>] (unregister_netdev+0x28/0x30)
[  536.677381]  r6:7f01003c r5:82492000 r4:82492000
[  536.682000] [<808bfa98>] (unregister_netdev) from [<7f000b40>] (usbnet_disconnect+0x64/0xdc [usbnet])
[  536.691241]  r5:82492000 r4:82492580
[  536.694819] [<7f000adc>] (usbnet_disconnect [usbnet]) from [<8076b958>] (usb_unbind_interface+0x80/0x248)
[  536.704406]  r5:7f01003c r4:83306c80
[  536.707984] [<8076b8d8>] (usb_unbind_interface) from [<8061765c>] (device_release_driver_internal+0x1c4/0x1cc)
[  536.718005]  r10:8112bcc0 r9:80dff1dc r8:83306c80 r7:83744000 r6:7f01003c r5:00000000
[  536.725838]  r4:8291e420
[  536.728373] [<80617498>] (device_release_driver_internal) from [<80617684>] (device_release_driver+0x20/0x24)
[  536.738302]  r7:83744000 r6:810d4f4c r5:8291e420 r4:8176ae30
[  536.743963] [<80617664>] (device_release_driver) from [<806156cc>] (bus_remove_device+0xf0/0x148)
[  536.752858] [<806155dc>] (bus_remove_device) from [<80610018>] (device_del+0x198/0x41c)
[  536.760880]  r7:83744000 r6:8116e2e4 r5:8291e464 r4:8291e420
[  536.766542] [<8060fe80>] (device_del) from [<80768fe8>] (usb_disable_device+0xcc/0x1e0)
[  536.774576]  r10:8112bcc0 r9:80dff1dc r8:00000001 r7:8112bc48 r6:8291e400 r5:00000001
[  536.782410]  r4:83306c00
[  536.784945] [<80768f1c>] (usb_disable_device) from [<80769c30>] (usb_set_configuration+0x514/0x8dc)
[  536.794011]  r10:00000000 r9:00000000 r8:832c3600 r7:00000004 r6:810d5688 r5:00000000
[  536.801844]  r4:83306c00
[  536.804379] [<8076971c>] (usb_set_configuration) from [<80775fac>] (usb_generic_driver_disconnect+0x34/0x38)
[  536.814236]  r10:832c3610 r9:83745ef8 r8:832c3600 r7:00000004 r6:810d5688 r5:83306c00
[  536.822069]  r4:83306c00
[  536.824605] [<80775f78>] (usb_generic_driver_disconnect) from [<8076b850>] (usb_unbind_device+0x30/0x70)
[  536.834100]  r5:83306c00 r4:810d5688
[  536.837678] [<8076b820>] (usb_unbind_device) from [<8061765c>] (device_release_driver_internal+0x1c4/0x1cc)
[  536.847432]  r5:822fb480 r4:83306c80
[  536.851009] [<80617498>] (device_release_driver_internal) from [<806176a8>] (device_driver_detach+0x20/0x24)
[  536.860853]  r7:00000004 r6:810d4f4c r5:810d5688 r4:83306c80
[  536.866515] [<80617688>] (device_driver_detach) from [<80614d98>] (unbind_store+0x70/0xe4)
[  536.874793] [<80614d28>] (unbind_store) from [<80614118>] (drv_attr_store+0x30/0x3c)
[  536.882554]  r7:00000000 r6:00000000 r5:83739200 r4:80614d28
[  536.888217] [<806140e8>] (drv_attr_store) from [<8035cb68>] (sysfs_kf_write+0x48/0x54)
[  536.896154]  r5:83739200 r4:806140e8
[  536.899732] [<8035cb20>] (sysfs_kf_write) from [<8035be84>] (kernfs_fop_write_iter+0x11c/0x1d4)
[  536.908446]  r5:83739200 r4:00000004
[  536.912024] [<8035bd68>] (kernfs_fop_write_iter) from [<802b87fc>] (vfs_write+0x258/0x3e4)
[  536.920317]  r10:00000000 r9:83745f58 r8:83744000 r7:00000000 r6:00000004 r5:00000000
[  536.928151]  r4:82adacc0
[  536.930687] [<802b85a4>] (vfs_write) from [<802b8b0c>] (ksys_write+0x74/0xf4)
[  536.937842]  r10:00000004 r9:007767a0 r8:83744000 r7:00000000 r6:00000000 r5:82adacc0
[  536.945676]  r4:82adacc0
[  536.948213] [<802b8a98>] (ksys_write) from [<802b8ba4>] (sys_write+0x18/0x1c)
[  536.955367]  r10:00000004 r9:83744000 r8:80100244 r7:00000004 r6:76f47b58 r5:76fc0350
[  536.963200]  r4:00000004
[  536.965735] [<802b8b8c>] (sys_write) from [<80100060>] (ret_fast_syscall+0x0/0x48)
[  536.973320] Exception stack(0x83745fa8 to 0x83745ff0)
[  536.978383] 5fa0:                   00000004 76fc0350 00000001 007767a0 00000004 00000000
[  536.986569] 5fc0: 00000004 76fc0350 76f47b58 00000004 76f47c7c 76f48114 00000000 7e87991c
[  536.994753] 5fe0: 00000498 7e879908 76e6dce8 76eca2e8
[  536.999922] ---[ end trace 9b835d809816b435 ]---

The driver should not be connecting and disconnecting the PHY when the
device is opened and closed, it should be stopping and starting the PHY. The
phy should be connected as part of binding and disconnected during
unbinding.

As this results in the PHY not being reset during open, link speed, etc.
settings set prior to the link coming up are now not being lost.

It is necessary for phy_stop() to only be called when the phydev still
exists (resolving the above stack trace). When unbinding, ".unbind" will be
called prior to ".stop", with phy_disconnect() already having called
phy_stop() before the phydev becomes inaccessible.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>
Cc: Steve Glendinning <steve.glendinning@shawell.net>
Cc: UNGLinuxDriver@microchip.com
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: stable@kernel.org # v5.15
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/smsc95xx.c

@@ -1050,6 +1050,14 @@ static const struct net_device_ops smsc95xx_netdev_ops = {
 	.ndo_set_features	= smsc95xx_set_features,
 };
 
+static void smsc95xx_handle_link_change(struct net_device *net)
+{
+	struct usbnet *dev = netdev_priv(net);
+
+	phy_print_status(net->phydev);
+	usbnet_defer_kevent(dev, EVENT_LINK_CHANGE);
+}
+
 static int smsc95xx_bind(struct usbnet *dev, struct usb_interface *intf)
 {
 	struct smsc95xx_priv *pdata;
@@ -1154,6 +1162,17 @@ static int smsc95xx_bind(struct usbnet *dev, struct usb_interface *intf)
 	dev->net->min_mtu = ETH_MIN_MTU;
 	dev->net->max_mtu = ETH_DATA_LEN;
 	dev->hard_mtu = dev->net->mtu + dev->net->hard_header_len;
+
+	ret = phy_connect_direct(dev->net, pdata->phydev,
+				 &smsc95xx_handle_link_change,
+				 PHY_INTERFACE_MODE_MII);
+	if (ret) {
+		netdev_err(dev->net, "can't attach PHY to %s\n", pdata->mdiobus->id);
+		goto unregister_mdio;
+	}
+
+	phy_attached_info(dev->net->phydev);
+
 	return 0;
 
 unregister_mdio:
@@ -1171,47 +1190,25 @@ static void smsc95xx_unbind(struct usbnet *dev, struct usb_interface *intf)
 {
 	struct smsc95xx_priv *pdata = dev->driver_priv;
 
+	phy_disconnect(dev->net->phydev);
 	mdiobus_unregister(pdata->mdiobus);
 	mdiobus_free(pdata->mdiobus);
 	netif_dbg(dev, ifdown, dev->net, "free pdata\n");
 	kfree(pdata);
 }
 
-static void smsc95xx_handle_link_change(struct net_device *net)
-{
-	struct usbnet *dev = netdev_priv(net);
-
-	phy_print_status(net->phydev);
-	usbnet_defer_kevent(dev, EVENT_LINK_CHANGE);
-}
-
 static int smsc95xx_start_phy(struct usbnet *dev)
 {
-	struct smsc95xx_priv *pdata = dev->driver_priv;
-	struct net_device *net = dev->net;
-	int ret;
+	phy_start(dev->net->phydev);
 
-	ret = smsc95xx_reset(dev);
-	if (ret < 0)
-		return ret;
-
-	ret = phy_connect_direct(net, pdata->phydev,
-				 &smsc95xx_handle_link_change,
-				 PHY_INTERFACE_MODE_MII);
-	if (ret) {
-		netdev_err(net, "can't attach PHY to %s\n", pdata->mdiobus->id);
-		return ret;
-	}
-
-	phy_attached_info(net->phydev);
-	phy_start(net->phydev);
 	return 0;
 }
 
-static int smsc95xx_disconnect_phy(struct usbnet *dev)
+static int smsc95xx_stop(struct usbnet *dev)
 {
-	phy_stop(dev->net->phydev);
-	phy_disconnect(dev->net->phydev);
+	if (dev->net->phydev)
+		phy_stop(dev->net->phydev);
+
 	return 0;
 }
 
@@ -1966,7 +1963,7 @@ static const struct driver_info smsc95xx_info = {
 	.unbind		= smsc95xx_unbind,
 	.link_reset	= smsc95xx_link_reset,
 	.reset		= smsc95xx_start_phy,
-	.stop		= smsc95xx_disconnect_phy,
+	.stop		= smsc95xx_stop,
 	.rx_fixup	= smsc95xx_rx_fixup,
 	.tx_fixup	= smsc95xx_tx_fixup,
 	.status		= smsc95xx_status,