[linux-dvb] Re: Slow i2c problem -- temporary patch

[Holger Waechtler <holger@convergence.de>]

Andrew de Quincey wrote:
> Here's a temporary patch (for dvb-kernel CVS head) for those trying out the 
> tda10045h driver. As per Robert's suggestion, I have upped the i2c bitrate to 
> 275kHz, and I've reduced the delay while waiting for the i2c status.
>
> Issues:
> 1) Is there a reason for the i2c bitrate to be set to 10kHz right now? Perhaps 
> some cards have very slow i2c components? It is fine on the tda10045h-based 
> cards
no, most DVB i2c components work up to 400kHz, some work up to 1MHz.


> 2) I've changed the wait-for-status-delay to use mdelay()... which is not 
> ideal as we are now effectively busy waiting, but the current 1 jiffy delay 
> is WAY too much at the new speed. At 275kHz, it doesn't  delay for long 
> enough for this to be significant though.
I modified your patch so that we use busy waiting only the first 10 
trials, thenafter we call the scheduler so that the system won't lock up 
for some 1/10s seconds in the worst case.

Please play a little with the actual number of trials we should to 
busy-waiting, I can't test this since I neither have a desktop PC with 
PCI slots nor a DVB card here.

> 3) If you reduce the i2c bitrate again (say back to 10kHz), your machine will 
> appear to hang. This is because it is having to delay for much longer for the 
> transmission to complete, and therefore the busy wait implied by mdelay() 
> becomes significant
>
> Later, I'll submit a better patch with rate-adaptive delays, but for now, I'd 
> definitely recommend using this if you're testing the tda driver.
Please create your patches in the future using 'cvs -q diff -pu', 
context patches are much easier to review.

As said above, I was not able to test the changes I commited, please 
test and report if there are problems.

many thanks,

Holger



--
Info:
To unsubscribe send a mail to ecartis@linuxtv.org with "unsubscribe linux-dvb" as subject.