[linux-dvb] [BUG] changeset 9029 (http://linuxtv.org/hg/v4l-dvb/rev/aa3e5cc1d833)
stoth at linuxtv.org
Tue Feb 17 16:16:55 CET 2009
Trent Piepho wrote:
> On Mon, 16 Feb 2009, Steven Toth wrote:
>>> Hartmut, Oliver and Trent: Thanks for helping with this issue. I've just
>>> reverted the changeset. We still need a fix at dm1105, au0828-dvb and maybe
>>> other drivers that call the filtering routines inside IRQ's.
>> Fix the demux, add a worker thread and allow drivers to call it directly.
>> I'm not a big fan of videobuf_dvb or having each driver do it's own thing as an
>> Fixing the demux... Would this require and extra buffer copy? probably, but it's
>> a trade-off between the amount of spent during code management on a driver by
>> driver basis vs wrestling with videobuf_dvb and all of problems highlighted on
>> the ML over the last 2 years.
> Have the driver copy the data into the demuxer from the interrupt handler
> with irqs disabled? That's still too much.
> The right way to do it is to have a queue of DMA buffers. In the interrupt
> handler the driver takes the completed DMA buffer off the "to DMA" queue
> and puts it in the "to process" queue. The driver should not copy and
> cetainly not demux the data from the interrupt handler.
I know what the right way is Trent (see cx23885) although thank you for
reminding me. videobuf_dvb hasn't convinced people like me to bury myself in its
mess or complexity during retro fits cases. Retro fitting videobuf_dvb into cx18
(at the time) was way too much effort.
Retro fitting it into existing drivers can be painful and I haven't seen any
volunteers stand up over the last 24 months to get this done.
My suggestion? For the most part we're talking about very low data rates for
DVB, coupled with fast memory buses for memcpy's. If the group doesn't want
calls to the sw_filter methods then implement a half-way-house replacement for
those drivers - as I mentioned above - with the memcpy. Either this approach, or
make videobuf_dvb mandatory and deprecate sw_filter_...n() to intensionally
break drivers and force maintainers to comply. This will upset people.
Realistically, this thread will probably go on for a couple of days then trail
off into nothing. The subject will rear it's head again in a few months, like
it's done in the past.
A general question to the group: Who wants to volunteer to retro fit
videobuf_dvb into the current drivers so we can avoid calls to sw_filter_...n()
I'm willing to loan any hardware I have to the volunteer assuming we can work
out something on shipping.
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