[linux-dvb] [PATCH] Add driver specific module option to choose dvb adapter numbers, second try

Rudy Zijlstra rudy at grumpydevil.homelinux.org
Wed Apr 9 18:14:42 CEST 2008



On Wed, 9 Apr 2008, Michael Krufky wrote:

> On Wed, Apr 9, 2008 at 11:07 AM, Manu Abraham <abraham.manu at gmail.com> wrote:
>> Janne Grunau wrote:
>> > Hi,
>> >
>> > I resubmit this patch since I still think it is a good idea to the this
>> > driver option. There is still no udev recipe to guaranty stable dvb
>> > adapter numbers. I've tried to come up with some rules but it's tricky
>> > due to the multiple device nodes in a subdirectory. I won't claim that
>> > it is impossible to get udev to assign driver or hardware specific
>> > stable dvb adapter numbers but I think this patch is easier and more
>> > clean than a udev based solution.
>> >
>> > I'll drop this patch if a simple udev solution is found in a reasonable
>> > amount of time. But if there is no I would like to see the attached
>> > patch merged.
>>
>>  As i wrote sometime back, adding adapter numbers to adapters is bad.
>>
>>  In fact, when the kernel advocates udev, working around it is no
>>  solution, but finding the problem and fixing the basic problem is more
>>  important, rather than workarounds.
>>
>>  http://www.gentoo.org/doc/en/udev-guide.xml
>>  http://reactivated.net/writing_udev_rules.html
>>
>>  If there is a general udev issue, it should be taken up with udev and
>>  not working around within adapter drivers.
>
> Regardless of how broken the issue is within udev, udev is not user-friendly.
>
> Under the current situation, users that have media recording servers
> that receive broadcasts from differing delivery systems have no way
> ensure that they are using the correct device for their recordings.
>
> For instance:
>
> Users might have VSB devices and QAM devices in their system, both to
> receive OTA broadcasts and digital cable.  Likewise, someone else
> might have DVB-S devices and DVB-T devices in the same system.
>
> If said user has VSB devices as adapters 0 and 1, QAM-capable devices
> as adapters 2 and 3, and DVB-S devices as adapters 5 and 6, they need
> to be able to configure their software to know which device to use
> when attempting to receive broadcasts from the respective media type.
>
> The argument that "udev should do this -- fix udev instead" is weak,
> in my opinion.  Even if udev can be fixed, the understanding of how to
> configure it is hopeless.
>
> When support for cx88-alsa and saa7134-alsa appeared, at first, I lost
> functionality of my sound card.  I fixed the issue by setting my alsa
> driver "index" module option for each respecting device in my build
> scripts.  If I didn't have the ability to rectify that issue, I simply
> would have yanked out the conflicting device (ie: use NO video card in
> the system) or just reboot into Windows and ditch Linux, altogether.
>
> This is a simple patch that adds the same functionality that v4l and
> alsa have -- the ability to declare the adapter number of the device
> at attach-time, based on a module option.  The change has minimal
> impact on the source code, and adds great benefits to the users, and
> requires zero maintenance.
>
> The arguments against applying this change are "fix udev instead" and
> "we'll have to remove this in kernel 2.7" ... Well, rather than to
> have everybody wait around for a "fix" that requires programming
> skills in order to use, I say we merge this now, so that people can
> use their systems properly TODAY.  If we have to remove this in the
> future as a result of some other kernel-wide requirements, then we
> will cross that bridge when we come to it.
>
> I see absolutely no harm in implementing this feature now.
>
> -Mike
>

+1

For MythTv setups this is very much needed... for the reasons Mike very 
clearly stated.



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