Re: [PULL] http://linuxtv.org/hg/~mcisely/pvrusb2

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On Thu, 22 Jan 2009 22:12:08 +0100
Thierry Merle <thierry.merle@xxxxxxx> wrote:

> Laurent Pinchart a écrit :
> > On Thursday 22 January 2009, Carsten Meier wrote:
> >> Am Thu, 22 Jan 2009 00:20:00 +0100
> >>
> >> schrieb Laurent Pinchart <laurent.pinchart@xxxxxxxxx>:
> >>> Hi Carsten,
> >>>
> >>> On Wednesday 21 January 2009, Carsten Meier wrote:
> >>>> 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.
> >>>
> >>>> 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,
> >>>
> >>> 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
> > 
> >> 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
> > 
> >> 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.
> > 
> 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.

Hi Thierry,

It may be a good idea to add some code at the v4l2-apps dir for retrieving the
sysfs place. Maybe we may add it at qv4l2 and at v4l2-ctl.

Cheers,
Mauro
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