However, and possibly out of line, but should we consider submitting a patch to remove the pullups by default for exynos that Doug hinted at? Cheers, Karl P On Wed, Oct 29, 2014 at 03:34:27PM +0100, NEO-Technologies / Julien CHAUVEAU wrote: > 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 écrit : > >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 Stübner 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 > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
