Trying to boot custom kernel on Wink Hub (i.MX28)

[Fabio Estevam]

Hi Rogan,

On Sun, Sep 24, 2023 at 5:16 PM Rogan Dawes <rogan at dawes.za.net> wrote:
>
> Hi folks,
>
> I eventually decided that I did need to figure out the DRAM timings for the Micron chip on my board, but I found an easier way than actually "understanding what I'm doing"! :-)
>
> I pulled the vendor U-Boot image off the flash, skipped the appropriate number of bytes until I was actually dealing with a u-boot.sb formatted image (looking for the STMP signature I found in the compiled mainline u-boot), then used the Rockbox project's sbtoelf tool to convert the SB back to two ELF files, the SPL.elf and the u-boot.elf. From there I loaded the SPL.elf into ghidra, then went looking for byte sequences found in arch/arm/cpu/arm926ejs/mxs/spl_mem_init.c to see if I could locate them in the vendor blob. I did, right at the end of the binary, then converted bytes into uint32 sequences so that I could compare with the mxs_dram_vals for CONFIG_MX28.
>
> Did the compare and found a single bit that is different between the two sequences of initialisation values. Literally a 1 to a 0, and that is all. So I built mainline with that change, and an updated iomux_setup because the Wink Hub v1 uses MX28_PAD_I2C0_SCL__DUART_RX and MX28_PAD_I2C0_SDA__DUART_TX for its console pins. i was hoping to see it boot via mxsldr, but unfortunately, I got nothing.

Ideally, you should create a new imx28-wink_defconfig.

For a quick test, besides changing iomux_setup, please make sure that
arch/arm/dts/imx28-evk.dts also has the duart pins changed.

> How can I get the SPL to emit something on the console to confirm it is running? i.e. before the DRAM initialisation?

SPL runs from the internal RAM, and should print something to the
console prior to the DRAM init.