Reading GPIOs with DM_GPIO before device tree is loaded

[Simon Glass]

Hi Hugo,

On Wed, 20 Jul 2022 at 04:54, Hugo Villeneuve <hugo at hugovil.com> wrote:
>
> 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;
> }
>
> ========================================

Well driver model needs the device tree to init, for example DM_GPIO
cannot operate without one unless you are hacking around with
platdata, which is a bit of a pain.

One option you might have is to use a general DT before relocation,
then figure out which one you really want to use and select that for
post relocation. That works better with driver model.

Regards,
Simon