[linux-dvb] Re: More than 4 DVB cards - again

[Michael Hunold <hunold@convergence.de>]

Hello,

On 06/22/04 10:27, Peter Maersk-Moller wrote:
> Seriously, using "extended minor number". How do I do that ?
> Are you talking about changing something in a config file
> or are you talking about rewriting the device driver ?
This must be changed in the dvb-core device handling.

> What is the limitation regarding more DVB devices than 4 ?
There can be 9 different types of devices per adapter 
(video,audio,sec,frontend,demux,dvr,ca, net) and each device can be 
present up to 4 times (ie. demux0, demux1, demux2, demux3)

Because everything needs to be a power of two, one adapter consumes 
16*4=64 minor numbers. Because of the fact you only have 256 minor 
numbers you're stuck with 4 adapters.

For 2.4 alone, the devfs implementation wasn't tied to major/minor 
numbers, so if you used devfs alone it was possible to support more that 
4 adapters.

In 2.6 this has changed -- devfs is now more tightly coupled and is 
limited to major/minor numbers again.

But: major/minor numbers have been extended from 8 to 16 bit types, so 
it should be possible to support more devices, but this also affects the 
surrounding system (ie. glibc must support this)

Additionally, udev/sysfs should be support which also overcomes this 
limitation.

But AFAIK nobody has worked on these problems so far, so ideas and 
patches are welcome.

> Kind regards
> --PMM
CU
Michael.