Reading GPIOs with DM_GPIO before device tree is loaded

[Hugo Villeneuve]

Hi,
in board_early_init_f(), i call a custom function get_som_revision() to read 
some GPIOs that are used to determine the SOM revision. This function basically 
sets the iomux, and then uses gpio_request/gpio_direction_input/gpio_get_value 
functions to read the GPIOs. Then, this SOM revision information is used in  
board_fit_config_name_match() to decide which device tree to load.

This works perfectly fine without CONFIG_DM_GPIO. However, if I enable 
CONFIG_DM_GPIO, it doesn't work anymore. There is an error when calling 
gpio_request().

What is the correct way to read GPIOs BEFORE any device tree is loaded?

My board uses an MX6Q SOM.

Here is part of the code I am using:

========================================
static iomux_v3_cfg_t const boardcfg_pads[] = {
        MX6_PAD_DISP0_DAT15__GPIO5_IO09 | MUX_PAD_CTRL(NO_PAD_CTRL),
        MX6_PAD_DISP0_DAT8__GPIO4_IO29  | MUX_PAD_CTRL(NO_PAD_CTRL),
        MX6_PAD_DISP0_DAT0__GPIO4_IO21  | MUX_PAD_CTRL(NO_PAD_CTRL),
        MX6_PAD_ENET_RXD0__GPIO1_IO27   | MUX_PAD_CTRL(NO_PAD_CTRL),
        MX6_PAD_ENET_RXD1__GPIO1_IO26   | MUX_PAD_CTRL(NO_PAD_CTRL),
};

static int som_revision = -1;

static const int boardcfg_gpio[] = {
        IMX_GPIO_NR(5, 9),
        IMX_GPIO_NR(4, 29),
        IMX_GPIO_NR(4, 21),
        IMX_GPIO_NR(1, 27),
        IMX_GPIO_NR(1, 26),
};

static void get_som_revision(void)
{
        int i;
        int rc;

        som_revision = 0;

        SETUP_IOMUX_PADS(boardcfg_pads);

        for (i = 0; i < ARRAY_SIZE(boardcfg_gpio); ++i) {
                int v;

                rc = gpio_request(boardcfg_gpio[i], "som-revision-gpio");
                if (rc) {
                        printf("%s(): gpio request %d failed\n", __func__, i);
                        som_revision = -1;
                        return;
                }

                gpio_direction_input(boardcfg_gpio[i]);
                v = gpio_get_value(boardcfg_gpio[i]);

                if ((v == 0) || (v == 1))
                        som_revision |= v << i;
                else {
                        som_revision = -1;
                        return;
                }
        }
}

int board_early_init_f(void)
{
        setup_iomux_uart();
        get_som_revision();

        return 0;
}

========================================



Thank you,
Hugo Villeneuve.