Re: PROBLEM: USB keyboards works only 4 per PC host port

On Monday 18 August 2008 8:44:32 pm Randy Dunlap wrote:

On Mon, 18 Aug 2008 16:42:49 +0530 Aivils Stoss wrote:

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On Friday 15 August 2008 7:19:48 am Randy Dunlap wrote:

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On Sun, 10 Aug 2008 04:08:37 +0100 Aivils Stoss wrote:

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On Saturday 09 August 2008 11:42:26 am Samuel Thibault wrote:

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Aivils Stoss, le Fri 08 Aug 2008 07:02:24 +0100, a écrit :

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I suppose this is Linux kernel bug because i test keyboards under
Windows, which support any schema of cascading of usb hubs.

On the very same machine and hubs?

Yes, on same machine. Under Windows i don't have evdev interface,
checked only how keypress go to console.
Of course to repeat a try You must have at least 5 keyboards and
1 7-port or 2 4-port hubs and kernel 2.6.22 and above. I allways
got result - 5th, 6th, 7th keyboard does not send events to console
or evdev.

[adding linux-usb mailing list]

Hi,

I finally got 5 USB keyboards together along with 2 hubs.
I daisy-chained the hubs and connected 1 keyboard to the hub that is
on the notebook computer USB port, then I connected 4 keyboards to the
second hub.  They all worked for me, meaning that I can type on all of
them and have their characters show up on my console.

I'm testing with 2.6.7-rc2.
'usbtree' output of the USB subsystem is attached.

Yeah! 2.6.7 is a bit obsolete. At my end 2.6.15 support more than 4
keyboards per PC port , but mess up input when is plugged more than
9 keyboards. 10th is capable to send keypress events, but last pressed
key will be repeated until ctrl-c . 10th keyboard disturb an auto repeat
of all keyboards.

Sorry, my keyboard made a typo.  I'm testing with 2.6.27-rc2.

So the problem is now different from your original report, right?

No problem is same. Older kernels have another troubles.
2.6.22-1-mepis-smp
Quite stable. Have oops sometime inside evdev. Support up to 16 
USB keyboards, where 4 hubs are plugged into PC and 4 keyboards on
each hub. Any hub cascade support only 4 keyboards, where 5th or more
is registered but don't send input events. Oops inside evdev , when
USB keyboard unplugged. No slow down even all USB keyboards does
not work properly. My be this one support more than 16 keyboards, but
i don't have PC USB ports enough.

2.6.24-7
4 keyboards per port. If plug in 5th tend to total slow down with this one:
usb 2-1.1.1: reset low speed USB device using 
uhci_hcd and address 17
5th - means 5th keyboard in USB hub's cascade, which is plugged into
single PC USB port.

2.6.26
4 keyboards per port. If plug in 5th tend to total slow down.

2.6.27-rc3
Sorry Randy i cannot repeat Your achievement. This worse of all tested
kernels. I got working 3 USB keyboards, when i plug in 4th, all keyboards,
include PS/2 stop working. Kernel does not hung up. I can reach box
via net. dmesg , /proc/bus/input/devices attached. lsusb hung up.

Please notify me , if i should use 2.6.27-rc2 !

Aivils

What speed is the host port that the keyboards are connected to?
Could it be a USB bus bandwidth limitation?  (not that any code
checks for that)

I barely found 5 USB keyboards, so I surely can't test 10 or more.  ;)
I suppose that it will take some USB debug messages to attempt to see
what is going on...


---
~Randy
Linux Plumbers Conference, 17-19 September 2008, Portland, Oregon USA
http://linuxplumbersconf.org/