[mythtv-users] No /dev/dvb devices

R. G. Newbury newbury at mandamus.org
Mon Mar 19 18:27:46 UTC 2007

Michael T. Dean wrote:
> On 03/18/2007 02:17 PM, Yeechang Lee wrote:
>> Anthony Messina <amessina at messinet.com> says:
>>> i have the same issue as the previous poster.  since it worked for
>>> you, would you mind sharing your /etc/modprobe.conf?
>> I don't have any HD5000-related entries in my /etc/modprobe.conf.
> OP just needs to load cx88-dvb through his distro's supplied automatic 
> module-loading scripts (i.e. /etc/modules or /etc/sysconfig/modules or 
> /etc/modprobe/cx88-dvb or ... --ask on your distro's fora/mailing lists) 
> or through an appropriate modprobe.conf entry (the first is easier than 
> the second approach).  Note, also, that Linux 2.6.21 will likely fix the 
> issue causing cx88-dvb to fail to load automatically, so doing things 
> incorrectly (i.e. through auto-module-loading scripts) for such a short 
> time is not a big deal.

The problem here is that the new kernel is *too* good. Previously these 
cards were not as well recognized, and at least in Fedora, the modprobe 
entry prevailed. Then in 2.1.18 or 19, the kernel started recognizing 
both the analog and digital sides, and loads a module, apparently at 
random. This also seems to lock the modula, so that modprobe -r does not 
work. This appears to happen BEFORE modprobe is run (Could be wrong but 
I don't think so.)

If the dvb side gets loaded first, the analog can be loaded later but 
apparently, not the other way round.

The answer is two-fold. First, blacklist at least the analaog module 
(cx8800) in /etc/modrobe.d/blacklist. (This may be sufficient, but I am 
not sure.)

Secondly, unload the cx88xx module and then load the cx88_dvb module in 
rc.local with 'modprobe -r cx88xx' and 'modprobe cx88_dvb'. The cx88xx 
module is the base module, and removing it should remove all (any) 
loaded cx88 modules. The cx88_dvb load will pull in the modules that it 
depends on. You can see this with lsmod if you do this from a console 
after booting.

This should get you a /dev/dvb structure. If you want, you can load the 
cx8800 after the cx88_dvb and get the matching /dev/videox entry.

If you use this route, the /dev/video entry will follow any /dev/video 
devices created by any 'modprobe ivtv' lines in modprobe.conf as you 
arfe doing this AFTER modprobe.conf has been run.

I have not totally confirmed what happens with mythbackend when the 
/dev/dvb/adapater0 structure does not exist. I *think* that mythbackend 
gets confused when it tries to probe for a DVB card. Accordingly I have 
added 'service mythbackend restart' as the last line of my rc.local. 
This ensures that mythbackend is started after ther cx88_dvb module is 


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