Reading GPIOs with DM_GPIO before device tree is loaded

[Hugo Villeneuve]

On Wed, 20 Jul 2022 09:01:01 -0600
Simon Glass <sjg at chromium.org> wrote:

> 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

Hi Simon,
I finally fixed the problem by hacking the mxc_gpio driver and simply enabling the DM_FLAG_PRE_RELOC flag with this simple patch:

diff --git a/drivers/gpio/mxc_gpio.c b/drivers/gpio/mxc_gpio.c
index 3cc0e7f353..be2bc6d655 100644
--- a/drivers/gpio/mxc_gpio.c
+++ b/drivers/gpio/mxc_gpio.c
@@ -396,6 +396,7 @@ U_BOOT_DRIVER(gpio_mxc) = {
        .priv_auto      = sizeof(struct mxc_bank_info),
        .of_match = mxc_gpio_ids,
        .bind   = mxc_gpio_bind,
+       .flags  = DM_FLAG_PRE_RELOC,
 };
 
 DM_DRIVER_ALIAS(gpio_mxc, fsl_imx6q_gpio)

No other changes were required.

However, this is probably not a solution that would get accepted into mainline U-Boot, or not?

-- 
Hugo Villeneuve <hugo at hugovil.com>