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SubjectUSB-C device hotplug issue
Date
Hi all,

I have a question regarding the usb hub driver (drivers/usb/core/hub.c).

There is the following scenario. I am using the Lenovo T580 device with the Lenovo UltraDock CS18 docking station. If I plug an usb-c device to the docking station there is one device which will not be recognized (SanDisk Ultra USB-C Flash Drive, https://www.sandisk.com/home/mobile-device-storage/ultra-usb-type-c). An other usb-c devices (SanDisk Extreme 900 SSD, https://www.sandisk.com/home/ssd/extreme-900-ssd) works fine. I don’t have that much USB-C devices available, so there is one device working and the other one not.

I made some analysis of the situation where I attached the SanDisk Ultra USB-C Flash Drive.
I added some debug logs in drivers/usb/core/hub.c in port_event and hub_port_reset and activated all dynamic debug prints in hub.c. The output is the following:

[ 724.110784] usb 4-1-port1: XXX: port_event: portstatus: 0x2c0, portchange: 0x40!
[ 724.110789] usb 4-1-port1: link state change
[ 724.114953] usb 4-1-port1: do warm reset
[ 724.168109] usb 4-1-port1: not warm reset yet, waiting 50ms
[ 724.220768] usb 4-1-port1: not warm reset yet, waiting 200ms
[ 724.425188] usb 4-1-port1: XXX: hub_port_reset (before clear USB_PORT_FEAT_C_CONNECTION): 0x203, portchange: 0x1!
[ 724.425906] usb 4-1-port1: XXX: hub_port_reset (after clear USB_PORT_FEAT_C_CONNECTION): 0x203, portchange: 0x0!
[ 724.477429] hub 4-1:1.0: state 7 ports 4 chg 0000 evt 0002
[ 724.477980] usb 4-1-port1: XXX: port_event: portstatus: 0x203, portchange: 0x0!

The same situation with SanDisk Extreme 900 SSD:

[ 863.647484] hub 4-1:1.0: state 7 ports 4 chg 0000 evt 0002
[ 863.647965] usb 4-1-port1: XXX: port_event: portstatus: 0x203, portchange: 0x1!
[ 863.648305] usb 4-1-port1: status 0203, change 0001, 10.0 Gb/s
[ 863.758573] usb 4-1-port1: debounce total 100ms stable 100ms status 0x203
[ 863.773495] usb 4-1-port1: XXX: hub_port_reset (before clear USB_PORT_FEAT_C_CONNECTION): 0x203, portchange: 0x0!
[ 863.773699] usb 4-1-port1: XXX: hub_port_reset (after clear USB_PORT_FEAT_C_CONNECTION): 0x203, portchange: 0x0!
[ 863.826311] usb 4-1.1: new SuperSpeedPlus USB device number 6 using xhci_hcd
[ 863.840002] usb 4-1.1: udev 6, busnum 4, minor = 389
[ 863.840010] usb 4-1.1: New USB device found, idVendor=0781, idProduct=5593
[ 863.840014] usb 4-1.1: New USB device strings: Mfr=2, Product=3, SerialNumber=1
[ 863.840018] usb 4-1.1: Product: EXTREME900
[ 863.840022] usb 4-1.1: Manufacturer: SanDisk
[ 863.840026] usb 4-1.1: SerialNumber: 10000019DF56

So, at first I am wondering if the usb hub port was in USB_SS_PORT_LS_U3 if I attach the SanDisk Ultra USB-C Flash Drive. In case of the SanDisk Extreme 900 the usb hub port is in USB_SS_PORT_LS_U0. What’ the reason for that?

I read https://www.kernel.org/doc/html/v4.14/driver-api/usb/power-management.html. In this test usb core was bootet wird autosuspend=-1.Additionally the <hubdev-portX>/power/pm_qos_no_power_off sysfs variable is always set to 1. Nevertheless the hub port is in LS U3, but only using SanDisk Ultra USB-C Flash Drive.

I looked through the code and wondered why the USB_PORT_FEAT_C_CONNECTION bit is cleared at successful warm usb 3 reset in hub_port_reset.
In case of the Ultra USB-C Flash Drive at first the link state change is detected. Directly after executing the actual hub_port_reset the USB_PORT_FEAT_C_CONNECTION bit will change to 1. But the hub_port_reset code will set this bit to 0. At the next run the bit remains 0 and the connect_change flag in port_event will not be set. That means the USB_PORT_FEAT_C_CONNECTION flag will be cleared without taking it into account. That’s why this device will not be detected correctly.

If I modify the code in this way that I did’t clear the USB_PORT_FEAT_C_CONNECTION bit in hub_port_reset on warm usb3 reset this flag is still set during the next run. This makes sure that the connect_change flag in port_event is set and the usb device is detected correctly.
Is this code change correct or will it break other use cases? Are there any other ways to make the kernel detect that usb device at the docking station?

Please refer to the output of the modified usb_hub_reset code:

[ 121.566344] hub 4-1:1.0: state 7 ports 4 chg 0000 evt 0002
[ 121.566805] usb 4-1-port1: XXX: port_event: portstatus: 0x2c0, portchange: 0x40!
[ 121.566810] usb 4-1-port1: link state change
[ 121.573481] usb 4-1-port1: do warm reset
[ 121.625297] usb 4-1-port1: not warm reset yet, waiting 50ms
[ 121.677854] usb 4-1-port1: not warm reset yet, waiting 200ms
[ 121.881091] usb 4-1-port1: XXX: hub_port_reset (before clear USB_PORT_FEAT_C_CONNECTION): 0x203, portchange: 0x1!
[ 121.881454] usb 4-1-port1: XXX: hub_port_reset (after clear USB_PORT_FEAT_C_CONNECTION): 0x203, portchange: 0x1!
[ 121.933109] hub 4-1:1.0: state 7 ports 4 chg 0000 evt 0002
[ 121.933407] usb 4-1-port1: XXX: port_event: portstatus: 0x203, portchange: 0x1!
[ 121.933861] usb 4-1-port1: status 0203, change 0001, 10.0 Gb/s
[ 122.042540] usb 4-1-port1: debounce total 100ms stable 100ms status 0x203
[ 122.056865] usb 4-1-port1: XXX: hub_port_reset (before clear USB_PORT_FEAT_C_CONNECTION): 0x203, portchange: 0x0!
[ 122.057230] usb 4-1-port1: XXX: hub_port_reset (after clear USB_PORT_FEAT_C_CONNECTION): 0x203, portchange: 0x0!
[ 122.109166] usb 4-1.1: new SuperSpeed USB device number 5 using xhci_hcd
[ 122.122392] usb 4-1.1: udev 5, busnum 4, minor = 388
[ 122.122399] usb 4-1.1: New USB device found, idVendor=0781, idProduct=5596
[ 122.122404] usb 4-1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 122.122408] usb 4-1.1: Product: Ultra T C
[ 122.122412] usb 4-1.1: Manufacturer: SanDisk
[ 122.122415] usb 4-1.1: SerialNumber: 4C531001400624115002
[ 122.124151] hub 4-1:1.0: state 7 ports 4 chg 0000 evt 0002
[ 122.125042] usb 4-1-port1: XXX: port_event: portstatus: 0x203, portchange: 0x0!


The code change for Kernel 4.14 look as follows:

Subject: [PATCH] usb: core: do not clear USB_PORT_FEAT_C_CONNECTION on warm
hub port reset

Signed-off-by: Dennis Wassenberg <dennis.wassenberg@secunet.com>
---
drivers/usb/core/hub.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index a9db0887edca..9b4dfe6c8829 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2815,7 +2815,9 @@ static int hub_port_reset(struct usb_hub *hub, int port1,
USB_PORT_FEAT_C_BH_PORT_RESET);
usb_clear_port_feature(hub->hdev, port1,
USB_PORT_FEAT_C_PORT_LINK_STATE);
- usb_clear_port_feature(hub->hdev, port1,
+
+ if (!warm)
+ usb_clear_port_feature(hub->hdev, port1,
USB_PORT_FEAT_C_CONNECTION);

/*
--
2.17.1

Thank you for your help!

Best regards,

Dennis

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