AM4376: gpiochip: Persistence not supported for GPIO

Hi Gunter,

The expert whom this thread is assigned to is already out of the office for the holidays.

I reviewed the kernel (v4.19) gpio driver, and believe GPIO persistence is not supported on AM437x, there is no configuration to enable such support.

You can see in kernel function gpiod_set_transitory() in gpiolib.c, which the kernel message is printed, the flag packed is set with PIN_CONFIG_PERSIST_STATE, then calls the platform driver's set_config() function.

2774         packed = pinconf_to_config_packed(PIN_CONFIG_PERSIST_STATE,             
2775                                           !transitory);                         
2776         gpio = gpio_chip_hwgpio(desc);                                          
2777         rc = chip->set_config(chip, gpio, packed);

For AM437x, set_config() is defined as omap_gpio_set_config() in gpio-omap.c, which only supports setting INPUT_DEBOUNCE.

1076         if (pinconf_to_config_param(config) != PIN_CONFIG_INPUT_DEBOUNCE)       
1077                 return -ENOTSUPP; 

By the way, the kernel message "Persistence not supported for GPIO xxx" is a kernel debug message, which is only informative. You won't see such message if kernel debug is not enabled.