U-Boot DM device tree and Linux device tree - what are the differences and why?

[Rudolf J Streif]

I have a custom board that is similar to the i.MX6UL 14x14. One
difference is that it has an eMMC rather than a SD card. Most recently I
upgraded from u-boot 2019.07 to u-boot 2020.01 and now u-boot cannot
detect the eMMC anymore.

For the 2019.07 version I did use CONFIG_FSL_ESDHC=y without
CONFIG_DM_MMC. That does not work anymore. Compilation fails with
"CONFIG_SYS_FSL_ESDHC_ADDR undefined". What has changed here and why?

Then I tried using CONFIG_FSL_USDHC=y and CONFIG_DM_MMC=y. I simply used
the device tree from the Linux kernel which works just fine for the
kernel. But it does not work for u-boot. It's hard to understand why.
Why would the u-boot device tree be different than the kernel device
tree? If that is even the issue.

It's an eMMC with 8-bit bus. Here are the definitions that work
perfectly well for the Linux kernel:

&usdhc2 {
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_usdhc2>;
    bus-width = <8>;
    max-frequency = <200000000>;
    vmmc-supply = <&sw2_reg>;
    mmc-ddr-1_8v;
    cap-mmc-highspeed;
    non-removable;
    keep-power-in-suspend;
    status = "okay";
};

        pinctrl_usdhc2: usdhc2grp {
            fsl,pins = <
                MX6UL_PAD_NAND_RE_B__USDHC2_CLK        0x1b0d9 /*
eMMC_CLK */
                MX6UL_PAD_NAND_WE_B__USDHC2_CMD        0x1b0d9 /*
eMMC_CMD */
                MX6UL_PAD_NAND_ALE__USDHC2_RESET_B    0x1b0d9 /* eMMC_RST */
                MX6UL_PAD_NAND_DATA00__USDHC2_DATA0    0x1b0d9 /*
eMMC_DAT0 */
                MX6UL_PAD_NAND_DATA01__USDHC2_DATA1    0x1b0d9 /*
eMMC_DAT1 */
                MX6UL_PAD_NAND_DATA02__USDHC2_DATA2    0x1b0d9 /*
eMMC_DAT2 */
                MX6UL_PAD_NAND_DATA03__USDHC2_DATA3    0x1b0d9 /*
eMMC_DAT3 */
                MX6UL_PAD_NAND_DATA04__USDHC2_DATA4    0x1b0d9 /*
eMMC_DAT4 */
                MX6UL_PAD_NAND_DATA05__USDHC2_DATA5    0x1b0d9 /*
eMMC_DAT5 */
                MX6UL_PAD_NAND_DATA06__USDHC2_DATA6    0x1b0d9 /*
eMMC_DAT6 */
                MX6UL_PAD_NAND_DATA07__USDHC2_DATA7    0x1b0d9 /*
eMMC_DAT7 */
            >;
        };

Every time the eMMC is probed e.g 'mmc dev 1' it takes about a second
and then the response is 'MMC: no card present'.

I appreciate the help.

Thank you,
Rudi

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