Need advise with u-boot on SH-7785LCR

[Marek Vasut]

On 11/6/23 21:42, Simon Glass wrote:
> +Marek Vasut <marex at denx.de>
> +Vagrant Cascadian <vagrant at debian.org>
> 
> 
> On Mon, 6 Nov 2023 at 10:33, John Paul Adrian Glaubitz <
> glaubitz at physik.fu-berlin.de> wrote:
> 
>> Hi Simon!
>>
>> On Mon, 2023-11-06 at 10:24 -0700, Simon Glass wrote:
>>>> So, I assume, I should just be able to write u-boot.bin to
>> /dev/mtdblock0?
>>>
>>> Maybe, but you will likely brick the device if you have no other way
>>> to write to flash.
>>
>> The flash memory is actually on a daughter board that can be easily
>> replaced
>> and I have multiple of these daughter boards. It turns out that just
>> writing
>> the image to /dev/mtdblock0 works and I can boot the board into the freshly
>> flashed u-boot version.
>>
>> However, the u-boot version 2019.01 built from git won't work while the old
>> 2014.01 version that I copied onto disk from /dev/mtdblock0 does work when
>> flashing it to a second daughter board.
>>
>> So, flashing works indeed like this and I can successfully start u-boot
>> after
>> flashing it into /dev/mtdblock0. Now I just need to figure out what the
>> difference
>> between 2014.01 and 2019.01 is and why the latter doesn't work.

In U-Boot, parallel NOR flash is flashed by cp.b into the parallel NOR 
memory mapped address , there are hooks which do the NOR writing.