Marc Dietrich wrote at Tuesday, October 18, 2011 9:50 AM: > On Monday 17 October 2011 08:29:01 Stephen Warren wrote: > > Marc Dietrich wrote at Saturday, October 15, 2011 10:34 AM: > > > Am Samstag 15 Oktober 2011, 17:18:33 schrieb Leon Romanovsky: > > > > This fix updates the CDEV1 pinmux for the paz00 board to be as in the > > > > Harmony board. Paz00 board is originally based on Harmony design. > > > > > > the fact that this patch makes sound work on paz00 does not necessary mean > > > that this is the "right thing" to do. > > > > > First, the initial state should be > > > TRISTATE, because sound layer should switch between NORMAL/TRISTATE > > > automaticly to save some power. > > > > None of the other boards do that, and the drivers don't support it. I > > believe the clock would need to be started as soon as the audio driver > > module were loaded, and kept running as long as it was loaded, so there's > > not much chance of optimizing power here at the moment. > > Which driver? The whole ASoC driver stack. It may depend on the codec, but I assume that CDEV1 clock output should be running the whole time the ASoC codec driver is active. Alsa-devel would be the best place to ask about that kind of thing. ... > > I don't know why there's a pull-down there in the Android kernel; there's > > no need as far as I know, since it's a clock signal. I'd go so far as to > > believe that a pull-down would distort the clock signal slightly. > > Is there some docu somewhere about what PUPD_NORMAL and POPD_PULL_DOWN means? > I know the meaning of TRISTATE and PULL_DOWN/UP from electronics, but > that does not define what the NORMAL state is. "NORMAL" means no pull-up or pull-down, or not tri-stated. It's badly named. > I also don't see why you can't get a nice clock signal out of a pull down pin. > If inactive, the pin is high (e.g. +3.3V), while when active it is pulled to > zero (ok, it's logical inverted). Well, I may be wrong, but the pin will attempt to drive a nice symmetric signal, yet with a pull-up/down, there will be some slight drive on the wire that'll tend to pull the signal towards 0v/3.3v the whole time which will distort it. Whether this is a problem for this particular signal, pull-up/down strength, etc. is something I don't know. Certainly, the pull isn't actually needed AFAIK, so it may as well be removed. -- nvpublic -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
