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

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Date:	Mon, 18 Aug 2008 08:14:32 -0700
From:	Randy Dunlap <rdunlap@...otime.net>
To:	Aivils Stoss <aivils@...net.lv>
Cc:	lud <linux-usb@...r.kernel.org>,
	Samuel Thibault <samuel.thibault@...-lyon.org>,
	linux-input@...r.kernel.org, jkosina@...e.cz,
	linux-kernel@...r.kernel.org,
	linuxconsole-dev@...ts.sourceforge.net
Subject: Re: PROBLEM: USB keyboards works only 4 per PC host port

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

> On Friday 15 August 2008 7:19:48 am Randy Dunlap wrote:
> > On Sun, 10 Aug 2008 04:08:37 +0100 Aivils Stoss wrote:
> > > On Saturday 09 August 2008 11:42:26 am Samuel Thibault wrote:
> > > > Aivils Stoss, le Fri 08 Aug 2008 07:02:24 +0100, a écrit :
> > > > > 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?


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/
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