Re: [PATCH v2] ARM: dts: rockchip: use internal pull-up resistors on I2C busses

From: Max Schwarz
Date: Wed Oct 29 2014 - 10:03:13 EST

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In reply to: Karl Palsson: "Re: [PATCH v2] ARM: dts: rockchip: use internal pull-up resistors on I2C busses"
Next in thread: NEO-Technologies / Julien CHAUVEAU: "Re: [PATCH v2] ARM: dts: rockchip: use internal pull-up resistors on I2C busses"
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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.h
> > tml>
> > Am Dienstag, 28. Oktober 2014, 11:36:36 schrieb Julien CHAUVEAU:
> > > According to the I2C bus specification, it is required to use pull-up
> > > resistors on the clock and data lines. Probing the I2C busses with
> > > i2cdetect results in bad results when no devices are connected and no
> > > external resistors are used.
> > >
> > > This patch configures the I2C busses to use the internal pull-up
> > > resistors
> > > on the RK3066, RK3188 and RK3288 Rockchip processors. It should also be
> > > noted that these default pull settings match the original configuration
> > > on
> > > these SoCs.
> > >
> > > Below is the results of using i2cdetect on a I2C bus with no devices
> > > connected before (1) and after (2) applying this patch.
> > >
> > > (1) root@localhost:~# i2cdetect -y 3
> > >
> > > 0 1 2 3 4 5 6 7 8 9 a b c d e f
> > >
> > > 00: 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
> > > 10: 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f
> > > 20: 20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f
> > > 30: -- -- -- -- -- rk3x-i2c 2005a000.i2c: timeout, ipd: 0x81, state: 2
> > > -- rk3x-i2c 2005a000.i2c: timeout, ipd: 0x80, state: 2
> > > -- rk3x-i2c 2005a000.i2c: timeout, ipd: 0x80, state: 2
> > > -- rk3x-i2c 2005a000.i2c: timeout, ipd: 0x80, state: 3
> > > -- rk3x-i2c 2005a000.i2c: timeout, ipd: 0x80, state: 3
> > > -- rk3x-i2c 2005a000.i2c: timeout, ipd: 0x80, state: 3
> > > ...
> > >
> > > (2) root@localhost:~# i2cdetect -y 3
> > >
> > > 0 1 2 3 4 5 6 7 8 9 a b c d e f
> > >
> > > 00: -- -- -- -- -- -- -- -- -- -- -- -- --
> > > 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> > > 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> > > 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> > > 40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> > > 50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> > > 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> > > 70: -- -- -- -- -- -- -- --
> > >
> > > Signed-off-by: Julien CHAUVEAU <julien.chauveau@xxxxxxxxxxxxxxxxxxx>
> > > ---
> > > Changes since v1:
> > > - fix the rk3066a pull settings (only available is
> > > pull_none/pull_default)
> > > - remove the warnings in the results of i2cdetect
> > >
> > > arch/arm/boot/dts/rk3066a.dtsi | 20 ++++++++++----------
> > > arch/arm/boot/dts/rk3188.dtsi | 20 ++++++++++----------
> > > arch/arm/boot/dts/rk3288.dtsi | 24 ++++++++++++------------
> > > 3 files changed, 32 insertions(+), 32 deletions(-)
> > >
> > > diff --git a/arch/arm/boot/dts/rk3066a.dtsi
> > > b/arch/arm/boot/dts/rk3066a.dtsi index ad9c2db..dbc1a0b 100644
> > > --- a/arch/arm/boot/dts/rk3066a.dtsi
> > > +++ b/arch/arm/boot/dts/rk3066a.dtsi
> > > @@ -202,36 +202,36 @@
> > >
> > > i2c0 {
> > >
> > > i2c0_xfer: i2c0-xfer {
> > >
> > > - rockchip,pins = <RK_GPIO2 28 RK_FUNC_1 &pcfg_pull_none>,
> > > - <RK_GPIO2 29 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <RK_GPIO2 28 RK_FUNC_1 &pcfg_pull_default>,
> > > + <RK_GPIO2 29 RK_FUNC_1 &pcfg_pull_default>;
> > >
> > > };
> > >
> > > };
> > >
> > > i2c1 {
> > >
> > > i2c1_xfer: i2c1-xfer {
> > >
> > > - rockchip,pins = <RK_GPIO2 30 RK_FUNC_1 &pcfg_pull_none>,
> > > - <RK_GPIO2 31 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <RK_GPIO2 30 RK_FUNC_1 &pcfg_pull_default>,
> > > + <RK_GPIO2 31 RK_FUNC_1 &pcfg_pull_default>;
> > >
> > > };
> > >
> > > };
> > >
> > > i2c2 {
> > >
> > > i2c2_xfer: i2c2-xfer {
> > >
> > > - rockchip,pins = <RK_GPIO3 0 RK_FUNC_1 &pcfg_pull_none>,
> > > - <RK_GPIO3 1 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <RK_GPIO3 0 RK_FUNC_1 &pcfg_pull_default>,
> > > + <RK_GPIO3 1 RK_FUNC_1 &pcfg_pull_default>;
> > >
> > > };
> > >
> > > };
> > >
> > > i2c3 {
> > >
> > > i2c3_xfer: i2c3-xfer {
> > >
> > > - rockchip,pins = <RK_GPIO3 2 RK_FUNC_2 &pcfg_pull_none>,
> > > - <RK_GPIO3 3 RK_FUNC_2 &pcfg_pull_none>;
> > > + rockchip,pins = <RK_GPIO3 2 RK_FUNC_2 &pcfg_pull_default>,
> > > + <RK_GPIO3 3 RK_FUNC_2 &pcfg_pull_default>;
> > >
> > > };
> > >
> > > };
> > >
> > > i2c4 {
> > >
> > > i2c4_xfer: i2c4-xfer {
> > >
> > > - rockchip,pins = <RK_GPIO3 4 RK_FUNC_1 &pcfg_pull_none>,
> > > - <RK_GPIO3 5 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <RK_GPIO3 4 RK_FUNC_1 &pcfg_pull_default>,
> > > + <RK_GPIO3 5 RK_FUNC_1 &pcfg_pull_default>;
> > >
> > > };
> > >
> > > };
> > >
> > > diff --git a/arch/arm/boot/dts/rk3188.dtsi
> > > b/arch/arm/boot/dts/rk3188.dtsi
> > > index ddaada7..ee2865f 100644
> > > --- a/arch/arm/boot/dts/rk3188.dtsi
> > > +++ b/arch/arm/boot/dts/rk3188.dtsi
> > > @@ -188,36 +188,36 @@
> > >
> > > i2c0 {
> > >
> > > i2c0_xfer: i2c0-xfer {
> > >
> > > - rockchip,pins = <RK_GPIO1 24 RK_FUNC_1 &pcfg_pull_none>,
> > > - <RK_GPIO1 25 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <RK_GPIO1 24 RK_FUNC_1 &pcfg_pull_up>,
> > > + <RK_GPIO1 25 RK_FUNC_1 &pcfg_pull_up>;
> > >
> > > };
> > >
> > > };
> > >
> > > i2c1 {
> > >
> > > i2c1_xfer: i2c1-xfer {
> > >
> > > - rockchip,pins = <RK_GPIO1 26 RK_FUNC_1 &pcfg_pull_none>,
> > > - <RK_GPIO1 27 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <RK_GPIO1 26 RK_FUNC_1 &pcfg_pull_up>,
> > > + <RK_GPIO1 27 RK_FUNC_1 &pcfg_pull_up>;
> > >
> > > };
> > >
> > > };
> > >
> > > i2c2 {
> > >
> > > i2c2_xfer: i2c2-xfer {
> > >
> > > - rockchip,pins = <RK_GPIO1 28 RK_FUNC_1 &pcfg_pull_none>,
> > > - <RK_GPIO1 29 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <RK_GPIO1 28 RK_FUNC_1 &pcfg_pull_up>,
> > > + <RK_GPIO1 29 RK_FUNC_1 &pcfg_pull_up>;
> > >
> > > };
> > >
> > > };
> > >
> > > i2c3 {
> > >
> > > i2c3_xfer: i2c3-xfer {
> > >
> > > - rockchip,pins = <RK_GPIO3 14 RK_FUNC_2 &pcfg_pull_none>,
> > > - <RK_GPIO3 15 RK_FUNC_2 &pcfg_pull_none>;
> > > + rockchip,pins = <RK_GPIO3 14 RK_FUNC_2 &pcfg_pull_up>,
> > > + <RK_GPIO3 15 RK_FUNC_2 &pcfg_pull_up>;
> > >
> > > };
> > >
> > > };
> > >
> > > i2c4 {
> > >
> > > i2c4_xfer: i2c4-xfer {
> > >
> > > - rockchip,pins = <RK_GPIO1 30 RK_FUNC_1 &pcfg_pull_none>,
> > > - <RK_GPIO1 31 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <RK_GPIO1 30 RK_FUNC_1 &pcfg_pull_up>,
> > > + <RK_GPIO1 31 RK_FUNC_1 &pcfg_pull_up>;
> > >
> > > };
> > >
> > > };
> > >
> > > diff --git a/arch/arm/boot/dts/rk3288.dtsi
> > > b/arch/arm/boot/dts/rk3288.dtsi
> > > index 874e66d..9a4b1f7 100644
> > > --- a/arch/arm/boot/dts/rk3288.dtsi
> > > +++ b/arch/arm/boot/dts/rk3288.dtsi
> > > @@ -636,43 +636,43 @@
> > >
> > > i2c0 {
> > >
> > > i2c0_xfer: i2c0-xfer {
> > >
> > > - rockchip,pins = <0 15 RK_FUNC_1 &pcfg_pull_none>,
> > > - <0 16 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <0 15 RK_FUNC_1 &pcfg_pull_up>,
> > > + <0 16 RK_FUNC_1 &pcfg_pull_up>;
> > >
> > > };
> > >
> > > };
> > >
> > > i2c1 {
> > >
> > > i2c1_xfer: i2c1-xfer {
> > >
> > > - rockchip,pins = <8 4 RK_FUNC_1 &pcfg_pull_none>,
> > > - <8 5 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <8 4 RK_FUNC_1 &pcfg_pull_up>,
> > > + <8 5 RK_FUNC_1 &pcfg_pull_up>;
> > >
> > > };
> > >
> > > };
> > >
> > > i2c2 {
> > >
> > > i2c2_xfer: i2c2-xfer {
> > >
> > > - rockchip,pins = <6 9 RK_FUNC_1 &pcfg_pull_none>,
> > > - <6 10 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <6 9 RK_FUNC_1 &pcfg_pull_up>,
> > > + <6 10 RK_FUNC_1 &pcfg_pull_up>;
> > >
> > > };
> > >
> > > };
> > >
> > > i2c3 {
> > >
> > > i2c3_xfer: i2c3-xfer {
> > >
> > > - rockchip,pins = <2 16 RK_FUNC_1 &pcfg_pull_none>,
> > > - <2 17 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <2 16 RK_FUNC_1 &pcfg_pull_up>,
> > > + <2 17 RK_FUNC_1 &pcfg_pull_up>;
> > >
> > > };
> > >
> > > };
> > >
> > > i2c4 {
> > >
> > > i2c4_xfer: i2c4-xfer {
> > >
> > > - rockchip,pins = <7 17 RK_FUNC_1 &pcfg_pull_none>,
> > > - <7 18 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <7 17 RK_FUNC_1 &pcfg_pull_up>,
> > > + <7 18 RK_FUNC_1 &pcfg_pull_up>;
> > >
> > > };
> > >
> > > };
> > >
> > > i2c5 {
> > >
> > > i2c5_xfer: i2c5-xfer {
> > >
> > > - rockchip,pins = <7 19 RK_FUNC_1 &pcfg_pull_none>,
> > > - <7 20 RK_FUNC_1 &pcfg_pull_none>;
> > > + rockchip,pins = <7 19 RK_FUNC_1 &pcfg_pull_up>,
> > > + <7 20 RK_FUNC_1 &pcfg_pull_up>;
> > >
> > > };
> > >
> > > };
> >
> > _______________________________________________
> > Linux-rockchip mailing list
> > Linux-rockchip@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/linux-rockchip

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Next message: Vlastimil Babka: "Re: + mm-compaction-avoid-premature-range-skip-in-isolate_migratepages_range.patch added to -mm tree"
Previous message: Arnaldo Carvalho de Melo: "Re: [PATCH 10/16] perf tools: Enhance the thread stack to output call/return data"
In reply to: Karl Palsson: "Re: [PATCH v2] ARM: dts: rockchip: use internal pull-up resistors on I2C busses"
Next in thread: NEO-Technologies / Julien CHAUVEAU: "Re: [PATCH v2] ARM: dts: rockchip: use internal pull-up resistors on I2C busses"
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