topic Re: DTS tree changes to access GPIO from linux on IMX6SL-EVK Board in i.MX Processors

DTS tree changes to access GPIO from linux on IMX6SL-EVK Board

deej — Mon, 31 Aug 2015 06:35:30 GMT

Hi all,

My problem exactly matches this discussion which doesn't seem to come to a resolution. Additionally, there are other discussions that get started, but never seems to find a resolution. If I manage to solve the issue, I'll post the solution here as well so that others will a tleast have something to go on.

I'm working on a IMX6SL-EVK board where I want to control a gpio pin from within linux. Currently, as a test platform I'm trying to control the LED that's connection to GPIO3:20 but haven't had much luck.

I'm running the kernel (Linux version 3.10.53) that is shipped with android KK by freescale.

The following is what I tried to perform the IO operation:

1. SYSFS GPIO access is enabled in the kernel

2. Modified iomux section in arch/arm/boot/dts/imx6sl-evk-common.dtsi to include the GPIO line in question as follows (see line 14)

&iomuxc {

pinctrl-names = "default", "sleep";

pinctrl-0 = <&pinctrl_hog>;

pinctrl-1 = <&pinctrl_hog_sleep>;

hog {

pinctrl_hog: hoggrp {

fsl,pins = <

MX6SL_PAD_KEY_ROW7__GPIO4_IO07 0x17059

MX6SL_PAD_KEY_COL7__GPIO4_IO06 0x17059

MX6SL_PAD_SD2_DAT7__GPIO5_IO00 0x17059

MX6SL_PAD_SD2_DAT6__GPIO4_IO29 0x17059

MX6SL_PAD_HSIC_STROBE__GPIO3_IO20 0xc7030

MX6SL_PAD_REF_CLK_32K__GPIO3_IO22 0x17059

MX6SL_PAD_FEC_TX_CLK__GPIO4_IO21 0x80000000

3. Issued the following commands from within linux to control the GPIOs

echo 84>/sys/class/gpio/export
echo out>/sys/class/gpio/gpio84/direction
echo -n 0x01>/sys/class/gpio/gpio84/value

I know the above command tries to access the GPIO port because, I've added some printk messages and see the results in the kernel log (this is issued from within static void bgpio_write32(void __iomem *reg, unsigned long data) in drivers/gpio/gpio-generic.c)

drivers/gpio/gpio-generic.c:87 a0828000=40f000

drivers/gpio/gpio-generic.c:87 a0828004=100000

However, the GPIO line itself doesn't change state.

I feel, I'm missing something in my dts configuration, but can't figure it out.

Thanks in advance.

Re: DTS tree changes to access GPIO from linux on IMX6SL-EVK Board

igorpadykov — Mon, 31 Aug 2015 12:38:29 GMT

Hi dee

according to linux documentation ...bindings/pinctrl/fsl,imx-pinctrl.txt :

Bits used for CONFIG:

NO_PAD_CTL(1 << 31): indicate this pin does not need config.

SION(1 << 30): Software Input On Field.

Force the selected mux mode input path no matter of MUX_MODE functionality.

By default the input path is determined by functionality of the selected

mux mode (regular).

One can try to change MX6SL_PAD_HSIC_STROBE__GPIO3_IO20 to 0x400c7030

Some examples can be found on

linux-imx6/imx6qdl-nit6xlite.dtsi at boundary-imx_3.10.53_1.1.1_ga · boundarydevices/linux-imx6 · GitHub

Other option to check/set GPIO register value with memtool

Best regards

igor

Re: DTS tree changes to access GPIO from linux on IMX6SL-EVK Board

fabio_estevam — Mon, 31 Aug 2015 13:34:23 GMT

Could you try applying/adapting this patch to 3.10?

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/arch/arm/boot/dts/imx6sl-evk.dts?id=d2c3936ebe88c…

Regards,

Fabio Estevam

Re: DTS tree changes to access GPIO from linux on IMX6SL-EVK Board

deej — Mon, 31 Aug 2015 23:24:36 GMT

Thanks for the reply Fabio, but that patch has already been applied.

Re: DTS tree changes to access GPIO from linux on IMX6SL-EVK Board

deej — Tue, 01 Sep 2015 00:28:53 GMT

The change to 0x400c7030 didn't address the issue. As to the other reference you gave, I tried it once earlier, but will try it again and post my changes for comment.

Thanks

Re: DTS tree changes to access GPIO from linux on IMX6SL-EVK Board

igorpadykov — Tue, 01 Sep 2015 01:34:53 GMT

could you check that HSIC_STROBE is not used somewhere as pwm2 ?

Also one can attach jtag and try to toggle this pin.

~igor

Re: DTS tree changes to access GPIO from linux on IMX6SL-EVK Board

deej — Tue, 01 Sep 2015 02:59:28 GMT

Finally figured out what was going on. My original STROBE pad setting was correct, however I didn't realise, the contents of DTS file that I was modifying was getting overridden by another file which is arch/arm/boot/dts/imx6sl-evk-csi.dts. After adding the STROBE entry in that file, I'm able to control the GPIO line through the sysfs interface.

Thanks for all your help.