Disable pullups on ConnectCard i.mx28 for GPIO use

Question

My goal is to use ConnectCard i.mx28 pins 18, 20, 22, 24, and 26 (SSP0_CMD, SSP0_DATA0, SSP0_DATA1, SSP0_DATA2, and SSP0_DATA3, respectively) for GPIO. My problem is that the pins seem to have an internal pullup I just can't clear. I've done what I believe to be an exhaustive effort to clear the pullups:

- Added "config_dts disable '_ssp0_'" to linux-dey_3.10.bb to not initialize those pins with the SSP0 peripheral.

- This didn't have any effect, so I went nuclear and removed all references to ssp0, mmc0, and spi0 from imx28.dtsi.

- Still no effect, so I added some pinctrl stanzas to imx28.dtsi to explicitly disable the pullups:

+ myboard: myboard@0 {
+ reg = <0>;
+ fsl,pinmux-ids = <
+ 0x2000 /* MX28_PAD_SSP0_DATA0__SSP0_D0 */
+ 0x2010 /* MX28_PAD_SSP0_DATA1__SSP0_D1 */
+ 0x2020 /* MX28_PAD_SSP0_DATA2__SSP0_D2 */
+ 0x2030 /* MX28_PAD_SSP0_DATA3__SSP0_D3 */
+ 0x2080 /* MX28_PAD_SSP0_CMD__SSP0_CMD */
+ 0x20a0 /* MX28_PAD_SSP0_SCK__SSP0_SCK */
+ >;
+ fsl,drive-strength = <0>;
+ fsl,voltage = <1>;
+ fsl,pull-up = <0>;
+ };

- Still no effect, so I went looking for other methods to disable the pullup. On page 1008 of the i.MX28 manual, I found this:

"HW_OCOTP_ROM1:0x8002C1B0:17 SSP0_EXT_PULLUP - Blow this bit to disable the internal pull-ups for SSP0 DATA and CMD signals."

So I used this command in uboot to blow the efuse:

otp blow 0x19 0x00020000

uboot now indicates it's blown:
CCARDIMX28 # otp dump
...
HW_OCOTP_ROMn
HW_OCOTP_ROMn0: 0x00000000
HW_OCOTP_ROMn1: 0x00020000
...

And it's still pulled high!

root@ccardimx28js:~# echo 72 > /sys/class/gpio/export
root@ccardimx28js:~# echo out > /sys/class/gpio/gpio72/direction
root@ccardimx28js:~# echo 0 > /sys/class/gpio/gpio72/value
root@ccardimx28js:~# cat /sys/class/gpio/gpio72/value
1


How do I disable this pullup?

Answer 1

Please take a look at this document:
https://www.kernel.org/doc/Documentation/devicetree/bindings/pinctrl/fsl,mxs-pinctrl.txt
I beleive it explains how to disable pull-ups via device tree

Comments

This is one of the things I tried. Please refer to the code pasted into my question. Do you know why this code doesn't work?

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have you tried to implement the example in the link as is without any changes? does it disable pull up on mmc-cd and mmc-sck pins?

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it looks like some pins do not have an internal pull-up control, so make sure you use the pin that does: https://lkml.org/lkml/2013/3/31/117
https://git.geekli.st/pirej/kernel/commit/d8880a126d96ba0f9e0191826431650c24711d47

also found another example here:
https://git.congatec.com/arm/imx6_kernel_3.14/blob/87311d0455fb92cb6ad5ef539c9351a22c02e53a/Documentation/devicetree/bindings/pinctrl/fsl,mxs-pinctrl.txt

---

I have not used the example without changes for a few reasons:
- I am using DEY Linux 3.10, which has a different syntax for pin definitions.
- The example behavior is already present in DEY: https://github.com/digidotcom/yocto-linux/blob/v3.10/dey-1.6/maint/arch/arm/boot/dts/imx28.dtsi#L509-L524

I have no trouble disabling pullups on most pins. For example, I had no trouble disabling the pullup on SSP0_CARD_DETECT. Specifically, SSP0_CMD, SSP0_DATA0, SSP0_DATA1, SSP0_DATA2, and SSP0_DATA3 are the pins I have not been successful in disabling the pullups on.

The problem is that these pins are pulled high, not missing pullups as some of your links describe.