Hi Doug, Le 29/10/2014 05:45, Doug Anderson a écrit :
Julien, On Tue, Oct 28, 2014 at 3:36 AM, Julien CHAUVEAU <julien.chauveau@xxxxxxxxxxxxxxxxxxx> wrote: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(-)I won't NAK this change myself, but I have to say I'm not a huge fan. On exynos boards the i2c has pulls by default, so there is precedent for what you're proposing at least. ...but I'll also say that most sane boards have external pulls on i2c and don't rely on the internal pulls. If you've got a board where the internal pull works well enough (lucky you!) then I think you should override the pinctrl for just that board.
At the SoC level, it is IMHO better to enable the internal pull-up resistors.
Because the files rk3066a.dtsi, rk3188.dtsi and rk3288.dtsi are not board-specific, I think it is wrong to presume that correct pull-up resistors are applied to the I2C lines on the board.
Furthermore, as I explained to Addy on the linux-rockchip mailing list, it is harmless to enable the internal pull-up resistors on the SoC, but of course you need to keep the external pull-up resistors on the board (so, do not remove them!).
Moreover, if you absolutely want to disable the internal pull-up resistors for one or another board, it is IMHO better to do it at the board level, but not at the SoC level.
To each is own... Julien/ // / -- 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
