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
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