How to identify USB-video-devices

How to identify USB-video-devices

[Carsten Meier]

Hello list,

we recently had a discussion on the pvrusb2-list on how to identify a
video-device connected via USB from an userspace app. (Or more precisely
on how to associate config-data with a particular device). This led to
a patch which returned the device's serial-no. in v4l2_capability's
bus_info field. This one has been rejected, but I really feel that this
is the right way to go. Here's the thread:
http://www.isely.net/pipermail/pvrusb2/2009-January/002091.html

I think the meaning of the bus_info-field should be modified slightly
for USB-devices to reflect its dynamic nature. At least a string that
won't change on dis-/reconnect and standby/wake-up-cycles should be
returned. If a device has a unique serial-no. it is a perfect candidate
for this, if not, some USB-port-info should be returned that won't
change if the device is connected to the same port through the same hub.

What do you think?
(BTW: I'm not a kernel-hacker, I'm writing this from the perspective of
an app-developer)

Regards,
Carsten

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Re: How to identify USB-video-devices

[Markus Rechberger]

On Thu, Jan 15, 2009 at 3:41 PM, Carsten Meier <cm@trexity.de> wrote:
> Hello list,
>
> we recently had a discussion on the pvrusb2-list on how to identify a
> video-device connected via USB from an userspace app. (Or more precisely
> on how to associate config-data with a particular device). This led to
> a patch which returned the device's serial-no. in v4l2_capability's
> bus_info field. This one has been rejected, but I really feel that this
> is the right way to go. Here's the thread:
> http://www.isely.net/pipermail/pvrusb2/2009-January/002091.html
>
> I think the meaning of the bus_info-field should be modified slightly
> for USB-devices to reflect its dynamic nature. At least a string that
> won't change on dis-/reconnect and standby/wake-up-cycles should be
> returned. If a device has a unique serial-no. it is a perfect candidate
> for this, if not, some USB-port-info should be returned that won't
> change if the device is connected to the same port through the same hub.
>
> What do you think?
> (BTW: I'm not a kernel-hacker, I'm writing this from the perspective of
> an app-developer)
>

write a few shellscripts and parse sysfs, or attach your application
to sysfs that it will
be notified if a device gets added. dbus is also a tip. no need to
hook up drivers
with some special things there.

regards,
Markus

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Re: How to identify USB-video-devices

[Carsten Meier]

Am Thu, 15 Jan 2009 16:20:23 +0100
schrieb "Markus Rechberger" <mrechberger@gmail.com>:

> On Thu, Jan 15, 2009 at 3:41 PM, Carsten Meier <cm@trexity.de> wrote:
> > Hello list,
> >
> > we recently had a discussion on the pvrusb2-list on how to identify
> > a video-device connected via USB from an userspace app. (Or more
> > precisely on how to associate config-data with a particular
> > device). This led to a patch which returned the device's serial-no.
> > in v4l2_capability's bus_info field. This one has been rejected,
> > but I really feel that this is the right way to go. Here's the
> > thread:
> > http://www.isely.net/pipermail/pvrusb2/2009-January/002091.html
> >
> > I think the meaning of the bus_info-field should be modified
> > slightly for USB-devices to reflect its dynamic nature. At least a
> > string that won't change on dis-/reconnect and
> > standby/wake-up-cycles should be returned. If a device has a unique
> > serial-no. it is a perfect candidate for this, if not, some
> > USB-port-info should be returned that won't change if the device is
> > connected to the same port through the same hub.
> >
> > What do you think?
> > (BTW: I'm not a kernel-hacker, I'm writing this from the
> > perspective of an app-developer)
> >
> 
> write a few shellscripts and parse sysfs, or attach your application
> to sysfs that it will
> be notified if a device gets added. dbus is also a tip. no need to
> hook up drivers
> with some special things there.
> 
> regards,
> Markus

But according to the docs, the bus_info-field is intended for the
purpose of identifying particular devices. Other solutions may be
possible, but they are much more complex and much more sensible to
other kernel-changes. By using bus_info, there is a simple and clean
solution that only depends on the V4L2-API and it also reflects the
primary intention of the field.

Other USB-device-drivers aren't required to change to the new policy,
their current bus_info-string (if implemented like in pvrusb2) changes
on every reconnect and standby/wake-up-cycle and is of no use anyway
for any app.

I really think that current behaviour is broken.

Regards,
Carsten

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Re: How to identify USB-video-devices

[Carsten Meier]

> 
> -----Original Message-----
> From: video4linux-list-bounces@redhat.com
> [mailto:video4linux-list-bounces@redhat.com] On Behalf Of Carsten
> Meier Sent: 15 janvier 2009 10:34 To: Markus Rechberger
> Cc: video4linux-list@redhat.com
> Subject: Re: How to identify USB-video-devices
> 
> Am Thu, 15 Jan 2009 16:20:23 +0100
> schrieb "Markus Rechberger" <mrechberger@gmail.com>:
>   
> > On Thu, Jan 15, 2009 at 3:41 PM, Carsten Meier <cm@trexity.de>
> > wrote:  
> > > Hello list,
> > >
> > > we recently had a discussion on the pvrusb2-list on how to
> > > identify a video-device connected via USB from an userspace app.
> > > (Or more precisely on how to associate config-data with a
> > > particular device). This led to a patch which returned the
> > > device's serial-no. in v4l2_capability's bus_info field. This one
> > > has been rejected, but I really feel that this is the right way
> > > to go. Here's the thread:
> > > http://www.isely.net/pipermail/pvrusb2/2009-January/002091.html
> > >
> > > I think the meaning of the bus_info-field should be modified
> > > slightly for USB-devices to reflect its dynamic nature. At least a
> > > string that won't change on dis-/reconnect and
> > > standby/wake-up-cycles should be returned. If a device has a
> > > unique serial-no. it is a perfect candidate for this, if not, some
> > > USB-port-info should be returned that won't change if the device
> > > is connected to the same port through the same hub.
> > >
> > > What do you think?
> > > (BTW: I'm not a kernel-hacker, I'm writing this from the
> > > perspective of an app-developer)
> > >  
> >
> > write a few shellscripts and parse sysfs, or attach your application
> > to sysfs that it will
> > be notified if a device gets added. dbus is also a tip. no need to
> > hook up drivers
> > with some special things there.
> >
> > regards,
> > Markus  
> 
> But according to the docs, the bus_info-field is intended for the
> purpose of identifying particular devices. Other solutions may be
> possible, but they are much more complex and much more sensible to
> other kernel-changes. By using bus_info, there is a simple and clean
> solution that only depends on the V4L2-API and it also reflects the
> primary intention of the field.
> 
> Other USB-device-drivers aren't required to change to the new policy,
> their current bus_info-string (if implemented like in pvrusb2) changes
> on every reconnect and standby/wake-up-cycle and is of no use anyway
> for any app.
> 
> I really think that current behaviour is broken.
> 
> Regards,
> Carsten
>   



Am Thu, 15 Jan 2009 10:55:40 -0500
schrieb Jonathan Lafontaine <jlafontaine@ctecworld.com>:

> I think that generic devices (often cheapest price) do not identify
> themselves exactly as well known trademarks.
> 
> So you can identify kind of chip they use (empia 2860) but, the
> eeprom space usb chips identity have, remain the
> responsibility/regardless to the company who build the entire video
> usb board and not the empia or otherelse chip you ask information on.
> 
> You can identify the vendor (2 letters id)so, in this situation,
> contact the vendor/company to get more precision about.
> 
> Try lsusb in terminal.
> 
> Hope this reply is usefull. Best regards, cheers  

Hi,

I think you misunderstood me or I misunderstood your message. :)

I don't want to recognize a particual device type (or brand), but I
want to distinguish two identical devices connected to a system.

Here comes the full story (again):

I'm currently writing a tool to store and apply configuration settings
like channel-frequencies and control-values. These should all be kept
in an XML-file which has a section for every v4l-device in the system.
Those sections are associated with a particular device by storing the
card- and bus_info-fields of the v4l2_capability-struct in the XML-file.

This works pretty well for PCI-cards, because the bus_info field never
changes (assuming you don't put the card in a different PCI-slot). This
use-case is exactly the one the bus_info field was made for.

But with USB things changed a bit. Now (at least for pvrusb2) a string
like "usb 7-2 address 6" is reported in bus_info. This is not
tragic, but after a disconnect-reconnect and even after a
standby-wakeup-cycle it reports a different string by increasing the
address no. Now I ask: Does anybody like to reconfigure an app just
because the laptop was idle and went to stand-by-mode?

Storing device-file-names is also not an option because they are
created dynamicly.

I can't say much about the sysfs-approach because I don't know much
about it. But it seems more complex and why depend on an external
mechanism if the V4L2-API already defines one?

Regards,
Carsten

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Re: How to identify USB-video-devices

[Pádraig Brady]

Carsten Meier wrote:
> Storing device-file-names is also not an option because they are
> created dynamicly.

You use udev rules to give persistent names.

Here is my /etc/udev/rules.d/video.rules file,
which creates /dev/webcam and /dev/tvtuner as appropriate.

KERNEL=="video*" SYSFS{name}=="USB2.0 Camera", NAME="video%n", SYMLINK+="webcam"
KERNEL=="video*" SYSFS{name}=="em28xx*", NAME="video%n", SYMLINK+="tvtuner"

To find distinguishing attributes to match on use:

echo /sys/class/video4linux/video* | xargs -n1 udevinfo -a -p

cheers,
Pádraig.

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Re: How to identify USB-video-devices

[Markus Rechberger]

On Thu, Jan 15, 2009 at 11:22 PM, Pádraig Brady <P@draigbrady.com> wrote:
> Carsten Meier wrote:
>> Storing device-file-names is also not an option because they are
>> created dynamicly.
>
> You use udev rules to give persistent names.
>
> Here is my /etc/udev/rules.d/video.rules file,
> which creates /dev/webcam and /dev/tvtuner as appropriate.
>
> KERNEL=="video*" SYSFS{name}=="USB2.0 Camera", NAME="video%n", SYMLINK+="webcam"
> KERNEL=="video*" SYSFS{name}=="em28xx*", NAME="video%n", SYMLINK+="tvtuner"
>
> To find distinguishing attributes to match on use:
>
> echo /sys/class/video4linux/video* | xargs -n1 udevinfo -a -p
>

yep, this is more or less what I meant too, although I didn't know
about udevinfo. I wonder if the output is consistent during the last
8(?) kernel releases because the sysfs structure changed, so I doubt
that actually.

regards,
Markus

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Re: How to identify USB-video-devices

[Carsten Meier]

Am Thu, 15 Jan 2009 22:22:11 +0000
schrieb Pádraig Brady <P@draigBrady.com>:

> Carsten Meier wrote:
> > Storing device-file-names is also not an option because they are
> > created dynamicly.
> 
> You use udev rules to give persistent names.
> 
> Here is my /etc/udev/rules.d/video.rules file,
> which creates /dev/webcam and /dev/tvtuner as appropriate.
> 
> KERNEL=="video*" SYSFS{name}=="USB2.0 Camera", NAME="video%n",
> SYMLINK+="webcam" KERNEL=="video*" SYSFS{name}=="em28xx*",
> NAME="video%n", SYMLINK+="tvtuner"
> 
> To find distinguishing attributes to match on use:
> 
> echo /sys/class/video4linux/video* | xargs -n1 udevinfo -a -p
> 
> cheers,
> Pádraig.

This already came up on the pvrusb2-list and someone told me (I don't
know much about udev) that it might cause problems on disconnection of
a device with a file-descriptor open which then gets reconnected
and there are two device-files for it. I also don't like it,
because an average user (including me) usually can't or don't want to
write udev rules. Finally v4l2 already contains a very simple and
reliable mechanism for doing this (bus_info-field) which simply isn't
used correctly by the USB-drivers.

My app should simply scan for /dev/video*-files, read out capabilities
from them, present the user menus to select devices and edit device
settings, save settings to a file and apply them on demand. This would
work fine if bus_info was filled right, without root-privileges,
without special udev rules or other sysfs-magic.

Regards,
Carsten

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Re: How to identify USB-video-devices

[Markus Rechberger]

On Thu, Jan 15, 2009 at 11:55 PM, Carsten Meier <cm@trexity.de> wrote:
> Am Thu, 15 Jan 2009 22:22:11 +0000
> schrieb Pádraig Brady <P@draigBrady.com>:
>
>> Carsten Meier wrote:
>> > Storing device-file-names is also not an option because they are
>> > created dynamicly.
>>
>> You use udev rules to give persistent names.
>>
>> Here is my /etc/udev/rules.d/video.rules file,
>> which creates /dev/webcam and /dev/tvtuner as appropriate.
>>
>> KERNEL=="video*" SYSFS{name}=="USB2.0 Camera", NAME="video%n",
>> SYMLINK+="webcam" KERNEL=="video*" SYSFS{name}=="em28xx*",
>> NAME="video%n", SYMLINK+="tvtuner"
>>
>> To find distinguishing attributes to match on use:
>>
>> echo /sys/class/video4linux/video* | xargs -n1 udevinfo -a -p
>>
>> cheers,
>> Pádraig.
>
> This already came up on the pvrusb2-list and someone told me (I don't
> know much about udev) that it might cause problems on disconnection of
> a device with a file-descriptor open which then gets reconnected
> and there are two device-files for it. I also don't like it,
> because an average user (including me) usually can't or don't want to
> write udev rules. Finally v4l2 already contains a very simple and
> reliable mechanism for doing this (bus_info-field) which simply isn't
> used correctly by the USB-drivers.
>

check the device serial for this one. I don't know if the pvrusb2
devices have it set up properly
I know some manufacturers don't do!
Be flexible with the node, but not with the serial.

cat /sys/class/video4linux/video0/device/serial
080702001788

you have the nodename in it, there are many ways to retrieve the nodename.

> My app should simply scan for /dev/video*-files, read out capabilities
> from them, present the user menus to select devices and edit device
> settings, save settings to a file and apply them on demand. This would
> work fine if bus_info was filled right, without root-privileges,
> without special udev rules or other sysfs-magic.
>
> Regards,
> Carsten
>
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Re: How to identify USB-video-devices

[Carsten Meier]

Am Fri, 16 Jan 2009 00:40:47 +0100
schrieb "Markus Rechberger" <mrechberger@gmail.com>:

> On Thu, Jan 15, 2009 at 11:55 PM, Carsten Meier <cm@trexity.de> wrote:
> > Am Thu, 15 Jan 2009 22:22:11 +0000
> > schrieb Pádraig Brady <P@draigBrady.com>:
> >
> >> Carsten Meier wrote:
> >> > Storing device-file-names is also not an option because they are
> >> > created dynamicly.
> >>
> >> You use udev rules to give persistent names.
> >>
> >> Here is my /etc/udev/rules.d/video.rules file,
> >> which creates /dev/webcam and /dev/tvtuner as appropriate.
> >>
> >> KERNEL=="video*" SYSFS{name}=="USB2.0 Camera", NAME="video%n",
> >> SYMLINK+="webcam" KERNEL=="video*" SYSFS{name}=="em28xx*",
> >> NAME="video%n", SYMLINK+="tvtuner"
> >>
> >> To find distinguishing attributes to match on use:
> >>
> >> echo /sys/class/video4linux/video* | xargs -n1 udevinfo -a -p
> >>
> >> cheers,
> >> Pádraig.
> >
> > This already came up on the pvrusb2-list and someone told me (I
> > don't know much about udev) that it might cause problems on
> > disconnection of a device with a file-descriptor open which then
> > gets reconnected and there are two device-files for it. I also
> > don't like it, because an average user (including me) usually can't
> > or don't want to write udev rules. Finally v4l2 already contains a
> > very simple and reliable mechanism for doing this (bus_info-field)
> > which simply isn't used correctly by the USB-drivers.
> >
> 
> check the device serial for this one. I don't know if the pvrusb2
> devices have it set up properly
> I know some manufacturers don't do!
> Be flexible with the node, but not with the serial.
> 
> cat /sys/class/video4linux/video0/device/serial
> 080702001788
> 
> you have the nodename in it, there are many ways to retrieve the
> nodename.

If I do a "ls /sys/class/video4linux/video0/" it simply prints:

dev  index  name  power  subsystem  uevent

and it will end up with many differnet cases to consider by any app. I
stay at my opinion that current bus_info-impl is broken. This *is* a
driver issue that needs fixing.

> 
> > My app should simply scan for /dev/video*-files, read out
> > capabilities from them, present the user menus to select devices
> > and edit device settings, save settings to a file and apply them on
> > demand. This would work fine if bus_info was filled right, without
> > root-privileges, without special udev rules or other sysfs-magic.
> >
> > Regards,
> > Carsten
> >
> > --
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> > mailto:video4linux-list-request@redhat.com?subject=unsubscribe
> > https://www.redhat.com/mailman/listinfo/video4linux-list
> >

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Re: How to identify USB-video-devices

[Markus Rechberger]

On Fri, Jan 16, 2009 at 1:27 AM, Carsten Meier <cm@trexity.de> wrote:
> Am Fri, 16 Jan 2009 00:40:47 +0100
> schrieb "Markus Rechberger" <mrechberger@gmail.com>:
>
>> On Thu, Jan 15, 2009 at 11:55 PM, Carsten Meier <cm@trexity.de> wrote:
>> > Am Thu, 15 Jan 2009 22:22:11 +0000
>> > schrieb Pádraig Brady <P@draigBrady.com>:
>> >
>> >> Carsten Meier wrote:
>> >> > Storing device-file-names is also not an option because they are
>> >> > created dynamicly.
>> >>
>> >> You use udev rules to give persistent names.
>> >>
>> >> Here is my /etc/udev/rules.d/video.rules file,
>> >> which creates /dev/webcam and /dev/tvtuner as appropriate.
>> >>
>> >> KERNEL=="video*" SYSFS{name}=="USB2.0 Camera", NAME="video%n",
>> >> SYMLINK+="webcam" KERNEL=="video*" SYSFS{name}=="em28xx*",
>> >> NAME="video%n", SYMLINK+="tvtuner"
>> >>
>> >> To find distinguishing attributes to match on use:
>> >>
>> >> echo /sys/class/video4linux/video* | xargs -n1 udevinfo -a -p
>> >>
>> >> cheers,
>> >> Pádraig.
>> >
>> > This already came up on the pvrusb2-list and someone told me (I
>> > don't know much about udev) that it might cause problems on
>> > disconnection of a device with a file-descriptor open which then
>> > gets reconnected and there are two device-files for it. I also
>> > don't like it, because an average user (including me) usually can't
>> > or don't want to write udev rules. Finally v4l2 already contains a
>> > very simple and reliable mechanism for doing this (bus_info-field)
>> > which simply isn't used correctly by the USB-drivers.
>> >
>>
>> check the device serial for this one. I don't know if the pvrusb2
>> devices have it set up properly
>> I know some manufacturers don't do!
>> Be flexible with the node, but not with the serial.
>>
>> cat /sys/class/video4linux/video0/device/serial
>> 080702001788
>>
>> you have the nodename in it, there are many ways to retrieve the
>> nodename.
>
> If I do a "ls /sys/class/video4linux/video0/" it simply prints:
>
> dev  index  name  power  subsystem  uevent
>
> and it will end up with many differnet cases to consider by any app. I
> stay at my opinion that current bus_info-impl is broken. This *is* a
> driver issue that needs fixing.
>

could it be that video0 is no usb device - or something else?
The usb-core framework should give you the information about the
serial id not the driver.

$ ls /sys/bus/usb/devices/*/id* /sys/bus/usb/devices/*/serial | while
read a; do cat $a; done
0c15 <- product
04fc <- vendor
00000CFD49 <- usb serial id
008e
0ccd
080702001788
6377
058f
920321111113
0000 <- nothing attached here
0000
0000:00:02.0
0000
0000
0000:00:02.1

$ lsusb
Bus 002 Device 008: ID 0ccd:008e TerraTec Electronic GmbH
Bus 002 Device 003: ID 058f:6377 Alcor Micro Corp.
Bus 002 Device 002: ID 04fc:0c15 Sunplus Technology Co., Ltd
Bus 002 Device 001: ID 0000:0000
Bus 001 Device 001: ID 0000:0000

I use kernel 2.6.24.21 here; but the sysfs entries have been available
for quite some time already.

Markus

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Re: How to identify USB-video-devices

[Carsten Meier]

Am Fri, 16 Jan 2009 01:59:51 +0100
schrieb "Markus Rechberger" <mrechberger@gmail.com>:

> On Fri, Jan 16, 2009 at 1:27 AM, Carsten Meier <cm@trexity.de> wrote:
> > Am Fri, 16 Jan 2009 00:40:47 +0100
> > schrieb "Markus Rechberger" <mrechberger@gmail.com>:
> >
> >> On Thu, Jan 15, 2009 at 11:55 PM, Carsten Meier <cm@trexity.de>
> >> wrote:
> >> > Am Thu, 15 Jan 2009 22:22:11 +0000
> >> > schrieb Pádraig Brady <P@draigBrady.com>:
> >> >
> >> >> Carsten Meier wrote:
> >> >> > Storing device-file-names is also not an option because they
> >> >> > are created dynamicly.
> >> >>
> >> >> You use udev rules to give persistent names.
> >> >>
> >> >> Here is my /etc/udev/rules.d/video.rules file,
> >> >> which creates /dev/webcam and /dev/tvtuner as appropriate.
> >> >>
> >> >> KERNEL=="video*" SYSFS{name}=="USB2.0 Camera", NAME="video%n",
> >> >> SYMLINK+="webcam" KERNEL=="video*" SYSFS{name}=="em28xx*",
> >> >> NAME="video%n", SYMLINK+="tvtuner"
> >> >>
> >> >> To find distinguishing attributes to match on use:
> >> >>
> >> >> echo /sys/class/video4linux/video* | xargs -n1 udevinfo -a -p
> >> >>
> >> >> cheers,
> >> >> Pádraig.
> >> >
> >> > This already came up on the pvrusb2-list and someone told me (I
> >> > don't know much about udev) that it might cause problems on
> >> > disconnection of a device with a file-descriptor open which then
> >> > gets reconnected and there are two device-files for it. I also
> >> > don't like it, because an average user (including me) usually
> >> > can't or don't want to write udev rules. Finally v4l2 already
> >> > contains a very simple and reliable mechanism for doing this
> >> > (bus_info-field) which simply isn't used correctly by the
> >> > USB-drivers.
> >> >
> >>
> >> check the device serial for this one. I don't know if the pvrusb2
> >> devices have it set up properly
> >> I know some manufacturers don't do!
> >> Be flexible with the node, but not with the serial.
> >>
> >> cat /sys/class/video4linux/video0/device/serial
> >> 080702001788
> >>
> >> you have the nodename in it, there are many ways to retrieve the
> >> nodename.
> >
> > If I do a "ls /sys/class/video4linux/video0/" it simply prints:
> >
> > dev  index  name  power  subsystem  uevent
> >
> > and it will end up with many differnet cases to consider by any
> > app. I stay at my opinion that current bus_info-impl is broken.
> > This *is* a driver issue that needs fixing.
> >
> 
> could it be that video0 is no usb device - or something else?
> The usb-core framework should give you the information about the
> serial id not the driver.
> 
> $ ls /sys/bus/usb/devices/*/id* /sys/bus/usb/devices/*/serial | while
> read a; do cat $a; done
> 0c15 <- product
> 04fc <- vendor
> 00000CFD49 <- usb serial id
> 008e
> 0ccd
> 080702001788
> 6377
> 058f
> 920321111113
> 0000 <- nothing attached here
> 0000
> 0000:00:02.0
> 0000
> 0000
> 0000:00:02.1
> 
> $ lsusb
> Bus 002 Device 008: ID 0ccd:008e TerraTec Electronic GmbH
> Bus 002 Device 003: ID 058f:6377 Alcor Micro Corp.
> Bus 002 Device 002: ID 04fc:0c15 Sunplus Technology Co., Ltd
> Bus 002 Device 001: ID 0000:0000
> Bus 001 Device 001: ID 0000:0000
> 
> I use kernel 2.6.24.21 here; but the sysfs entries have been available
> for quite some time already.
> 
> Markus

Yes, it is a pvr-usb-device with an mpeg-encoder which resides
under /sys/class/pvrusb2/. And exactly this difference shows that it
should be solved by the driver's bus_info-string and not by programming
this logic into an app.

OK, I'm done for today. I'm arguing this for two full days now. :(

Good night,
Carsten

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Re: How to identify USB-video-devices

[Markus Rechberger]

On Fri, Jan 16, 2009 at 2:55 AM, Carsten Meier <cm@trexity.de> wrote:
> Am Fri, 16 Jan 2009 01:59:51 +0100
> schrieb "Markus Rechberger" <mrechberger@gmail.com>:
>
>> On Fri, Jan 16, 2009 at 1:27 AM, Carsten Meier <cm@trexity.de> wrote:
>> > Am Fri, 16 Jan 2009 00:40:47 +0100
>> > schrieb "Markus Rechberger" <mrechberger@gmail.com>:
>> >
>> >> On Thu, Jan 15, 2009 at 11:55 PM, Carsten Meier <cm@trexity.de>
>> >> wrote:
>> >> > Am Thu, 15 Jan 2009 22:22:11 +0000
>> >> > schrieb Pádraig Brady <P@draigBrady.com>:
>> >> >
>> >> >> Carsten Meier wrote:
>> >> >> > Storing device-file-names is also not an option because they
>> >> >> > are created dynamicly.
>> >> >>
>> >> >> You use udev rules to give persistent names.
>> >> >>
>> >> >> Here is my /etc/udev/rules.d/video.rules file,
>> >> >> which creates /dev/webcam and /dev/tvtuner as appropriate.
>> >> >>
>> >> >> KERNEL=="video*" SYSFS{name}=="USB2.0 Camera", NAME="video%n",
>> >> >> SYMLINK+="webcam" KERNEL=="video*" SYSFS{name}=="em28xx*",
>> >> >> NAME="video%n", SYMLINK+="tvtuner"
>> >> >>
>> >> >> To find distinguishing attributes to match on use:
>> >> >>
>> >> >> echo /sys/class/video4linux/video* | xargs -n1 udevinfo -a -p
>> >> >>
>> >> >> cheers,
>> >> >> Pádraig.
>> >> >
>> >> > This already came up on the pvrusb2-list and someone told me (I
>> >> > don't know much about udev) that it might cause problems on
>> >> > disconnection of a device with a file-descriptor open which then
>> >> > gets reconnected and there are two device-files for it. I also
>> >> > don't like it, because an average user (including me) usually
>> >> > can't or don't want to write udev rules. Finally v4l2 already
>> >> > contains a very simple and reliable mechanism for doing this
>> >> > (bus_info-field) which simply isn't used correctly by the
>> >> > USB-drivers.
>> >> >
>> >>
>> >> check the device serial for this one. I don't know if the pvrusb2
>> >> devices have it set up properly
>> >> I know some manufacturers don't do!
>> >> Be flexible with the node, but not with the serial.
>> >>
>> >> cat /sys/class/video4linux/video0/device/serial
>> >> 080702001788
>> >>
>> >> you have the nodename in it, there are many ways to retrieve the
>> >> nodename.
>> >
>> > If I do a "ls /sys/class/video4linux/video0/" it simply prints:
>> >
>> > dev  index  name  power  subsystem  uevent
>> >
>> > and it will end up with many differnet cases to consider by any
>> > app. I stay at my opinion that current bus_info-impl is broken.
>> > This *is* a driver issue that needs fixing.
>> >
>>
>> could it be that video0 is no usb device - or something else?
>> The usb-core framework should give you the information about the
>> serial id not the driver.
>>
>> $ ls /sys/bus/usb/devices/*/id* /sys/bus/usb/devices/*/serial | while
>> read a; do cat $a; done
>> 0c15 <- product
>> 04fc <- vendor
>> 00000CFD49 <- usb serial id
>> 008e
>> 0ccd
>> 080702001788
>> 6377
>> 058f
>> 920321111113
>> 0000 <- nothing attached here
>> 0000
>> 0000:00:02.0
>> 0000
>> 0000
>> 0000:00:02.1
>>
>> $ lsusb
>> Bus 002 Device 008: ID 0ccd:008e TerraTec Electronic GmbH
>> Bus 002 Device 003: ID 058f:6377 Alcor Micro Corp.
>> Bus 002 Device 002: ID 04fc:0c15 Sunplus Technology Co., Ltd
>> Bus 002 Device 001: ID 0000:0000
>> Bus 001 Device 001: ID 0000:0000
>>
>> I use kernel 2.6.24.21 here; but the sysfs entries have been available
>> for quite some time already.
>>
>> Markus
>
> Yes, it is a pvr-usb-device with an mpeg-encoder which resides
> under /sys/class/pvrusb2/. And exactly this difference shows that it
> should be solved by the driver's bus_info-string and not by programming
> this logic into an app.
>
> OK, I'm done for today. I'm arguing this for two full days now. :(
>

I understand, it should be fixed in the driver yes.

good night,
Markus

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Re: How to identify USB-video-devices

[Mike Isely]

On Fri, 16 Jan 2009, Markus Rechberger wrote:

> On Fri, Jan 16, 2009 at 2:55 AM, Carsten Meier <cm@trexity.de> wrote:
> > Am Fri, 16 Jan 2009 01:59:51 +0100
> > schrieb "Markus Rechberger" <mrechberger@gmail.com>:
> >

   [...]

> >>
> >> could it be that video0 is no usb device - or something else?
> >> The usb-core framework should give you the information about the
> >> serial id not the driver.
> >>
> >> $ ls /sys/bus/usb/devices/*/id* /sys/bus/usb/devices/*/serial | while
> >> read a; do cat $a; done
> >> 0c15 <- product
> >> 04fc <- vendor
> >> 00000CFD49 <- usb serial id
> >> 008e
> >> 0ccd
> >> 080702001788
> >> 6377
> >> 058f
> >> 920321111113
> >> 0000 <- nothing attached here
> >> 0000
> >> 0000:00:02.0
> >> 0000
> >> 0000
> >> 0000:00:02.1
> >>
> >> $ lsusb
> >> Bus 002 Device 008: ID 0ccd:008e TerraTec Electronic GmbH
> >> Bus 002 Device 003: ID 058f:6377 Alcor Micro Corp.
> >> Bus 002 Device 002: ID 04fc:0c15 Sunplus Technology Co., Ltd
> >> Bus 002 Device 001: ID 0000:0000
> >> Bus 001 Device 001: ID 0000:0000
> >>
> >> I use kernel 2.6.24.21 here; but the sysfs entries have been available
> >> for quite some time already.
> >>
> >> Markus
> >
> > Yes, it is a pvr-usb-device with an mpeg-encoder which resides
> > under /sys/class/pvrusb2/. And exactly this difference shows that it
> > should be solved by the driver's bus_info-string and not by programming
> > this logic into an app.
> >
> > OK, I'm done for today. I'm arguing this for two full days now. :(
> >
> 
> I understand, it should be fixed in the driver yes.
> 

Markus:

Of course he's talking about the pvrusb2 driver.  This thread first 
started last week on the pvrusb2 mailing list and when Mauro rejected 
the resulting patch to adjust bus_info (something I also initially 
rejected but was convinced otherwise later), the discussion came here.

In an earlier reply you said that the usb-core should be responsible for 
the serial number.  Well in this case that's impossible.  For Hauppauge 
devices handled by this driver, the serial number is not in the USB 
config data, but held in a non-standard private device-resident I2C ROM 
that is read by the tveeprom module in v4l-dvb and made directly 
available to the pvrusb2 driver itself.  The information is not 
available as USB configuration data so there's no way for the USB core 
ever learn of the device's serial number.  Basically the vendor has set 
things up so that the serial number is intrinsic to the device instance 
itself not the particular connection mechanism (e.g. USB).

Of course, with all that said, I do agree that it would be very useful 
for that serial number to be available to udev (and thus it becomes 
visible in the sorts of ways that Mauro was suggesting).  I'm reasonably 
certain this is done by the pvrusb2 driver stuffing it into a magic 
kobject that is linked into a magic location.  But the last time I tried 
to figure this out, I came up completely empty.  Right now I don't know 
how to do this, and the LDD3 is too old apparently to describe it.  
Honestly there's probably more digging I can do but I've got other 
higher priority issues to contend with and since the bus_info strategy 
is off the table, this problem is still left unsolved.

I do find it disheartening that the querycap command can return all 
sorts of info about the device and it's too bad no allowance was ever 
made there to also include some sort of specific device-tagging unique 
(for a given device type) identifier, such as a serial number.  Carsten 
is trying to do something that should in concept be simple, but the 
response he's getting involves a lot of complexity instead :-(

  -Mike


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isely @ pobox (dot) com
PGP: 03 54 43 4D 75 E5 CC 92 71 16 01 E2 B5 F5 C1 E8

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