How to obtain sysfs-path from bus_info

Quoted 33 lines

Am Thu, 22 Jan 2009 00:20:00 +0100

schrieb Laurent Pinchart <[email protected]>:

Quoted 30 lines

Hi Carsten,

Quoted 5 lines · Carsten Meier

now I want to translate bus_info into a sysfs-path to obtain device-info like serial numbers. Given a device reports "usb-0000:00:1d.2-2" as bus_info, then the device-info is located under "/sys/bus/usb/devices/2-2", which is a symlink to the appropriate /sys/devices/ directory, right?

I'm afraid not. In the above bus_info value, 0000:00:1d.2 is the PCI bus path of your USB controller, and the last digit after the dash is the USB device path.

Quoted 6 lines

All I have to do is to compare the first 4 chars of bus_info against "usb-", get the chars after "." and append it to "/sys/bus/usb/devices/" to obatin a sysfs-path, right?

Is there a more elegant solution or already a function for this? Can the "." appear more than once before the last one?

Probably not before, but definitely after.

Root hubs get a USB device path set to '0'. Every other device is numbered according to the hub port number it is connected to. If you have an external hub connected on port 2 of your root hub, and have a webcam connected to port 3 of the external hub, usb_make_path() will return "usb-0000:00:1d.2-2.3".

Cheers,

Quoted 7 lines

Quoted 1 line

Laurent Pinchart

Hi,

On my machine, my pvrusb2 (connected directly to my mini-pc) shows up under "/sys/bus/usb/devices/7-2/" which is a symbolic link to "../../../devices/pci0000:00/0000:00:1d.7/usb7/7-2"

You're just lucky that USB bus 7 (usb7/7) is connected to the 7th function of your USB host controller (1d.7).

Here's an example of what I get on my computer:

/sys/bus/usb/devices/4-2
-> ../../../devices/pci0000:00/0000:00:1d.2/usb4/4-2

Quoted 3 lines

I can't test for the new bus_info-string, because it's not fixed yet in the driver. But if I got it correctly it should be "usb-0000:00:1d.7-7.2" ?

I think you will get usb-0000:00:1d.7-2

Quoted 3 lines

Then I've to simply take the string after the last dash, replace "." by "-" and append it to "/sys/bus/usb/devices/" for a sysfs-path?

Unfortunately the mapping is not that direct. The part before the last dash identifies the USB host controller. The part after the last dash identifies the device path related to the controller, expressed as a combination of port numbers.

The sysfs device path /sys/bus/usb/devices/7-2/ includes a USB bus number (in this case 7) that is not present in usb_make_path()'s output.

To find the sysfs path of your USB peripheral, you will have to find out which bus number the bus name (0000:00:1d.7) corresponds to. You might be able to find that by checking each usb[0-9]+ links in /sys/bus/usb/devices and comparing the link's target with the bus name.

Best regards,

Laurent Pinchart

Quoted 66 lines · Laurent Pinchart

Quoted 29 lines · Carsten Meier

Am Thu, 22 Jan 2009 00:20:00 +0100

schrieb Laurent Pinchart <[email protected]>:

Quoted 26 lines

Hi Carsten,

Quoted 5 lines · Carsten Meier

now I want to translate bus_info into a sysfs-path to obtain device-info like serial numbers. Given a device reports "usb-0000:00:1d.2-2" as bus_info, then the device-info is located under "/sys/bus/usb/devices/2-2", which is a symlink to the appropriate /sys/devices/ directory, right?

I'm afraid not. In the above bus_info value, 0000:00:1d.2 is the PCI bus path of your USB controller, and the last digit after the dash is the USB device path.

Quoted 6 lines

All I have to do is to compare the first 4 chars of bus_info against "usb-", get the chars after "." and append it to "/sys/bus/usb/devices/" to obatin a sysfs-path, right?

Is there a more elegant solution or already a function for this? Can the "." appear more than once before the last one?

Probably not before, but definitely after.

Root hubs get a USB device path set to '0'. Every other device is numbered according to the hub port number it is connected to. If you have an external hub connected on port 2 of your root hub, and have a webcam connected to port 3 of the external hub, usb_make_path() will return "usb-0000:00:1d.2-2.3".

Quoted 8 lines

Quoted 3 lines

Cheers,

Laurent Pinchart

Hi,

On my machine, my pvrusb2 (connected directly to my mini-pc) shows up under "/sys/bus/usb/devices/7-2/" which is a symbolic link to "../../../devices/pci0000:00/0000:00:1d.7/usb7/7-2"

You're just lucky that USB bus 7 (usb7/7) is connected to the 7th function of your USB host controller (1d.7).

Here's an example of what I get on my computer:

/sys/bus/usb/devices/4-2
-> ../../../devices/pci0000:00/0000:00:1d.2/usb4/4-2

Quoted 3 lines

I can't test for the new bus_info-string, because it's not fixed yet in the driver. But if I got it correctly it should be "usb-0000:00:1d.7-7.2" ?

I think you will get usb-0000:00:1d.7-2

Quoted 3 lines

Then I've to simply take the string after the last dash, replace "." by "-" and append it to "/sys/bus/usb/devices/" for a sysfs-path?

Unfortunately the mapping is not that direct. The part before the last dash identifies the USB host controller. The part after the last dash identifies the device path related to the controller, expressed as a combination of port numbers.

The sysfs device path /sys/bus/usb/devices/7-2/ includes a USB bus number (in this case 7) that is not present in usb_make_path()'s output.

Quoted 6 lines

To find the sysfs path of your USB peripheral, you will have to find out which bus number the bus name (0000:00:1d.7) corresponds to. You might be able to find that by checking each usb[0-9]+ links in /sys/bus/usb/devices and comparing the link's target with the bus name.

To ease this processing, using libsysfs can be a good idea... On my system, the documentation of libsysfs is here:
/usr/doc/sysfsutils-2.1.0/libsysfs.txt
Knowing the bus-id, it won't be hard to look at it in data structures. Just my 2 cents.