Understanding sysfs and USB

As we know the USB itself is a very complex peripheral to understand and work upon for development, due to such complexity the sysfs representation of USB bus and the peripherals attached to it is also complex.

We can now see how many root hubs our machine has as below,

$ cd /sys/bus/usb/devices

$ ls -al usb*
usb1 -> ../../../devices/pci0000:00/0000:00:14.0/usb1
usb2 -> ../../../devices/pci0000:00/0000:00:14.0/usb2

This shows that it has 2 root hubs. Now, lets try to correlate it with lsusb. A simple shell script which will print only RootHubs available on your machine.

$ vim lsusb.sh

#!/bin/sh
TOTAL_BUS_NUM=$1
for (( i=1; i <= $TOTAL_BUS_NUM; i++ ))
do
    lsusb -s $i:1
done

Run it as “bash lsusb.sh 2” [ Note: here 2 is the number of root hubs we seen in sysfs ]

$  bash lsusb.sh 2
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub

We can check the sysfs files for one particular device on a USB bus as,

$ tree ../../../devices/pci0000:00/0000:00:14.0/usb1/1-6/
../../../devices/pci0000:00/0000:00:14.0/usb1/1-6/
├── 1-6:1.0
│   ├── authorized
│   ├── bAlternateSetting
│   ├── bInterfaceClass
│   ├── bInterfaceNumber
│   ├── bInterfaceProtocol
│   ├── bInterfaceSubClass
│   ├── bNumEndpoints
│   ├── driver -> ../../../../../../bus/usb/drivers/rtsx_usb
│   ├── ep_01
│   │   ├── bEndpointAddress
│   │   ├── bInterval
│   │   ├── bLength
│   │   ├── bmAttributes
│   │   ├── direction
│   │   ├── interval
│   │   ├── power
│   │   │   ├── async
│   │   │   ├── autosuspend_delay_ms
│   │   │   ├── control
│   │   │   ├── runtime_active_kids
│   │   │   ├── runtime_active_time
│   │   │   ├── runtime_enabled
│   │   │   ├── runtime_status
│   │   │   ├── runtime_suspended_time
│   │   │   └── runtime_usage
│   │   ├── type
│   │   ├── uevent
│   │   └── wMaxPacketSize
│   ├── ep_82
│   │   ├── bEndpointAddress
│   │   ├── bInterval
│   │   ├── bLength
│   │   ├── bmAttributes
│   │   ├── direction
│   │   ├── interval
│   │   ├── power
│   │   │   ├── async
│   │   │   ├── autosuspend_delay_ms
│   │   │   ├── control
│   │   │   ├── runtime_active_kids
│   │   │   ├── runtime_active_time
│   │   │   ├── runtime_enabled
│   │   │   ├── runtime_status
│   │   │   ├── runtime_suspended_time
│   │   │   └── runtime_usage
│   │   ├── type
│   │   ├── uevent
│   │   └── wMaxPacketSize
│   ├── ep_83
│   │   ├── bEndpointAddress
│   │   ├── bInterval
│   │   ├── bLength
│   │   ├── bmAttributes
│   │   ├── direction
│   │   ├── interval
│   │   ├── power
│   │   │   ├── async
│   │   │   ├── autosuspend_delay_ms
│   │   │   ├── control
│   │   │   ├── runtime_active_kids
│   │   │   ├── runtime_active_time
│   │   │   ├── runtime_enabled
│   │   │   ├── runtime_status
│   │   │   ├── runtime_suspended_time
│   │   │   └── runtime_usage
│   │   ├── type
│   │   ├── uevent
│   │   └── wMaxPacketSize
│   ├── interface
│   ├── modalias
│   ├── power
│   │   ├── async
│   │   ├── runtime_active_kids
│   │   ├── runtime_enabled
│   │   ├── runtime_status
│   │   └── runtime_usage
│   ├── rtsx_usb_ms.2.auto
│   │   ├── driver -> ../../../../../../../bus/platform/drivers/rtsx_usb_ms
│   │   ├── driver_override
│   │   ├── memstick_host
│   │   │   └── memstick0
│   │   │       ├── device -> ../../../rtsx_usb_ms.2.auto
│   │   │       ├── power
│   │   │       │   ├── async
│   │   │       │   ├── autosuspend_delay_ms
│   │   │       │   ├── control
│   │   │       │   ├── runtime_active_kids
│   │   │       │   ├── runtime_active_time
│   │   │       │   ├── runtime_enabled
│   │   │       │   ├── runtime_status
│   │   │       │   ├── runtime_suspended_time
│   │   │       │   └── runtime_usage
│   │   │       ├── subsystem -> ../../../../../../../../../class/memstick_host
│   │   │       └── uevent
│   │   ├── modalias
│   │   ├── power
│   │   │   ├── async
│   │   │   ├── autosuspend_delay_ms
│   │   │   ├── control
│   │   │   ├── runtime_active_kids
│   │   │   ├── runtime_active_time
│   │   │   ├── runtime_enabled
│   │   │   ├── runtime_status
│   │   │   ├── runtime_suspended_time
│   │   │   └── runtime_usage
│   │   ├── subsystem -> ../../../../../../../bus/platform
│   │   └── uevent
│   ├── rtsx_usb_sdmmc.1.auto
│   │   ├── driver -> ../../../../../../../bus/platform/drivers/rtsx_usb_sdmmc
│   │   ├── driver_override
│   │   ├── leds
│   │   │   └── mmc0::
│   │   │       ├── brightness
│   │   │       ├── device -> ../../../rtsx_usb_sdmmc.1.auto
│   │   │       ├── max_brightness
│   │   │       ├── power
│   │   │       │   ├── async
│   │   │       │   ├── autosuspend_delay_ms
│   │   │       │   ├── control
│   │   │       │   ├── runtime_active_kids
│   │   │       │   ├── runtime_active_time
│   │   │       │   ├── runtime_enabled
│   │   │       │   ├── runtime_status
│   │   │       │   ├── runtime_suspended_time
│   │   │       │   └── runtime_usage
│   │   │       ├── subsystem -> ../../../../../../../../../class/leds
│   │   │       ├── trigger
│   │   │       └── uevent
│   │   ├── mmc_host
│   │   │   └── mmc0
│   │   │       ├── device -> ../../../rtsx_usb_sdmmc.1.auto
│   │   │       ├── power
│   │   │       │   ├── async
│   │   │       │   ├── autosuspend_delay_ms
│   │   │       │   ├── control
│   │   │       │   ├── runtime_active_kids
│   │   │       │   ├── runtime_active_time
│   │   │       │   ├── runtime_enabled
│   │   │       │   ├── runtime_status
│   │   │       │   ├── runtime_suspended_time
│   │   │       │   └── runtime_usage
│   │   │       ├── subsystem -> ../../../../../../../../../class/mmc_host
│   │   │       └── uevent
│   │   ├── modalias
│   │   ├── power
│   │   │   ├── async
│   │   │   ├── autosuspend_delay_ms
│   │   │   ├── control
│   │   │   ├── runtime_active_kids
│   │   │   ├── runtime_active_time
│   │   │   ├── runtime_enabled
│   │   │   ├── runtime_status
│   │   │   ├── runtime_suspended_time
│   │   │   └── runtime_usage
│   │   ├── subsystem -> ../../../../../../../bus/platform
│   │   └── uevent
│   ├── subsystem -> ../../../../../../bus/usb
│   ├── supports_autosuspend
│   └── uevent
├── authorized
├── avoid_reset_quirk
├── bcdDevice
├── bConfigurationValue
├── bDeviceClass
├── bDeviceProtocol
├── bDeviceSubClass
├── bmAttributes
├── bMaxPacketSize0
├── bMaxPower
├── bNumConfigurations
├── bNumInterfaces
├── busnum
├── configuration
├── descriptors
├── dev
├── devnum
├── devpath
├── driver -> ../../../../../bus/usb/drivers/usb
├── ep_00
│   ├── bEndpointAddress
│   ├── bInterval
│   ├── bLength
│   ├── bmAttributes
│   ├── direction
│   ├── interval
│   ├── power
│   │   ├── async
│   │   ├── autosuspend_delay_ms
│   │   ├── control
│   │   ├── runtime_active_kids
│   │   ├── runtime_active_time
│   │   ├── runtime_enabled
│   │   ├── runtime_status
│   │   ├── runtime_suspended_time
│   │   └── runtime_usage
│   ├── type
│   ├── uevent
│   └── wMaxPacketSize
├── firmware_node -> ../../../../LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:45/device:46/device:4d
├── idProduct
├── idVendor
├── ltm_capable
├── manufacturer
├── maxchild
├── port -> ../1-0:1.0/usb1-port6
├── power
│   ├── active_duration
│   ├── async
│   ├── autosuspend
│   ├── autosuspend_delay_ms
│   ├── connected_duration
│   ├── control
│   ├── level
│   ├── persist
│   ├── runtime_active_kids
│   ├── runtime_active_time
│   ├── runtime_enabled
│   ├── runtime_status
│   ├── runtime_suspended_time
│   ├── runtime_usage
│   ├── wakeup
│   ├── wakeup_abort_count
│   ├── wakeup_active
│   ├── wakeup_active_count
│   ├── wakeup_count
│   ├── wakeup_expire_count
│   ├── wakeup_last_time_ms
│   ├── wakeup_max_time_ms
│   └── wakeup_total_time_ms
├── product
├── quirks
├── removable
├── remove
├── rx_lanes
├── serial
├── speed
├── subsystem -> ../../../../../bus/usb
├── tx_lanes
├── uevent
├── urbnum
└── version

Reference’s

• http://www.makelinux.net/ldd3/chp-13-sect-2.shtml
• Allen Stern’s description