Linux/AM3352: How to keep the device's specific GPIO pins low when booting the device kernel.

Sh.Sasaki

Guru 13625 points

Part Number: AM3352

Tool/software: Linux

Hi everyone,

My customer wants to keep the device's specific GPIO pins low when booting the device kernel.

They set up the device tree referring to the following link. However, GPIO1_28 becomes High at kernel boot.

e2e.ti.com/.../684056
stackoverflow.com/.../am335x-gpio-muxing-in-device-tree-gets-reset-during-kernel-load

Device tree settings (partial excerpt)
----------------------------------------------------
&am33xx_pinmux {
reset_pins: pinmux_reset_pins {
pinctrl-single,pins = <
AM33XX_IOPAD(0x878, PIN_OUTPUT_PULLDOWN | MUX_MODE7 ) /* (U18) gpmc_be1n.gpio1[28] */
>;
};
};
----------------------------------------------------

I would like to know how to keep GPIO1_28 in low state at kernel boot.

My customer's Linux kernel is 4.9.59+ (2017 LTS).

Best regards,
Sasaki

over 7 years ago

0 Pavel Botev over 7 years ago

TI__Guru**** 170625 points

Sasaki,

From what I understand, you configure GPIO1_28 in u-boot and then you need to keep this configuration during kernel load and boot. If that is correct, you can try with updating the kernel GPIO1 DTS file with tehse entries: "ti,no-idle", "ti,no-idle-on-init" and "ti,no-reset-on-init", check below user guide for more details:

processors.wiki.ti.com/.../Early_Boot_and_Late_Attach_in_Linux

If that do not help, you can try also updating the u-boot DTS file with these entries, and modifying below file:

linux-kernel/arch/arm/mach-omap2/omap_hwmod_33xx_43xx_ipblock_data.c

Remove SYSC_HAS_SOFTRESET flag from am33xx_gpio_sysc

Regards,
Pavel

0 Sh.Sasaki over 7 years ago in reply to Pavel Botev

Guru 13625 points

Hi Pavel-san

Thank you for your support.

I will inform my customer about this and report the result here.

Best regards,

Sasaki

0 Sh.Sasaki over 7 years ago in reply to Sh.Sasaki

Guru 13625 points

Hi Pavel-san,

Thanks to your advice, My customer's problem has been resolved.

Best regards,
Sasaki

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Linux/AM3352: How to keep the device's specific GPIO pins low when booting the device kernel.