Hi everyone, Okay, I understand your opinion. So let's drop my patch in this case. Thank you for your comments. Julien Le 29/10/2014 15:02, Max Schwarz a ?crit : > Hi, > > I'll agree with Karl and Doug. If you (as a board vendor/maintainer/etc) want > to use I2C, it's *your* responsibility to provide the pullup resistors by > either including pullup resistors on the board or by enabling the internal > ones. > Either way, you should think a moment about the consequences (frequency/trace > length limitations), which is why I'm also against the pullup-by-default > behavior. > > Also, it's much harder to diagnose effects like Doug is describing (slightly > out-of-spec due to internal + external pulls) than the effects you are seeing > without any pullups. With your i2cdetect results my first thought would have > been "are there pullups on the bus?". > > Cheers, > Max > > Am Mittwoch, 29. Oktober 2014, 13:44:15 schrieb Karl Palsson: >> I'd be more inclined to have pulls disabled by default, it's more standard >> with what smaller micros do, but I've no experience with these bigger >> cortex-a parts. It's also the "least surprise" path. If you want to try >> and use the onboard pullups, you can specify that in your board file, but >> for people deliberately selecting pullups for their timing and load >> expectations, being required to take an extra step to turn off something >> seems unexpected. >> >> If you _want_ to be able to probe an i2c bus for devices added aftermarket, >> on a board that didn't get i2c pull ups because no devices were planned, >> and you want to turn on the internal pullups for that, I think that's >> something you need to do yourself, not making it a hard default in the SoC >> dtsi file. >> >> so, if it's off by default, you get this >> dtsi dts >> Board1, i2c periphs, designed pullups => off - >> board2, no peripsh, pulls in case => off - >> board3, no periphs, forgot pulls, pray=> off on >> >> If you turn it on by default, sure, it causes no harm in most cases, but >> you're no longer getting the values you expect, without having to turn off >> things that are not default anyway. >> >> Sincerely, >> Karl Palsson >> >> On Wed, Oct 29, 2014 at 02:17:23PM +0100, Heiko St?bner wrote: >>> Hi Addy, Max, Wolfram, >>> >>> after Doug's explanation of disfavour [0] and Julien's subsequent response >>> I'm not sure which direction to go. So if possible I'd like to collect >>> some more opinions of people knowing a lot more about i2c internals than >>> myself :-) . >>> >>> >>> Thanks >>> Heiko >>> >>> >>> [0] http://lists.infradead.org/pipermail/linux-rockchip/2014-October/000934.html
