[linux-dvb] [PATCH] function for checking if the dvb framework is idle

Michael Krufky mkrufky at linuxtv.org
Tue Aug 14 17:52:48 CEST 2007

Markus Rechberger wrote:
> On 8/14/07, Christoph Pfister <christophpfister at gmail.com> wrote:
>> Hi Markus,
>> [ although you shouldn't overrate my opinion here I'm giving my $0.02 ]
>> The problem with this approach are race conditions.
>> You can't reliably use the result of this function if you don't ensure
>> that no thread is started during / after the query. As far as I
>> understood your idea you try to solve this issue with the
>> allow-dvb-files-to-be-locked patch. But that patch doesn't handle file
>> descriptors which have been opened before you did the "lock".
>> Of course you can do additional work to fix that too - but imho the
>> easier (and safer from a design-pov) approach is to do the locking at
>> the bridge level as Steve did. I don't think that there are issues
>> with handling it there - as neither dvb-core nor the frontends access
>> the device directly (dvb-core via callbacks and the frontend via i2c
>> adapter). Or do I miss something here?
> There's some other code for checking if the filehandles are open but I
> don't need that patch to go into the framework, it will be stored in
> the local driver.
> For now my aim is to bring in the most needed patches in and nothing else.
> Markus


You seem to be avoiding the issue.

Christoph is trying to explain to you the same idea that I have tried to explain
to you in the past -- locking of the device for use between analog and digital
should take place at the bridge driver level.

This is what Steve Toth has done for the :8802 port in the cx88 driver, by only
allowing cx88-blackbird -or- cx88-dvb to use the hardware at any given moment.

Since it is the bridge hardware that determines whether or not the device is a
combo device (both analog and digital can be used concurrently) or a hybrid
device (only analog or digital can be used, one at a time), and it is the bridge
hardware itself, that has the limitation. the locking is only appropriate at the
level of the bridge driver itself.


Michael Krufky

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