linux_dsm_epyc7002/Documentation/arm/SH-Mobile/zboot-rom-sdhi.txt

ROM-able zImage boot from eSD
-----------------------------

An ROM-able zImage compiled with ZBOOT_ROM_SDHI may be written to eSD and
SuperH Mobile ARM will to boot directly from the SDHI hardware block.

This is achieved by the mask ROM loading the first portion of the image into
MERAM and then jumping to it. This portion contains loader code which
copies the entire image to SDRAM and jumps to it. From there the zImage
boot code proceeds as normal, uncompressing the image into its final
location and then jumping to it.

This code has been tested on an mackerel board using the developer 1A eSD
boot mode which is configured using the following jumper settings.

   8 7 6 5 4 3 2 1
   x|x|x|x| |x|x|
S4 -+-+-+-+-+-+-+-
    | | | |x| | |x on

The eSD card needs to be present in SDHI slot 1 (CN7).
As such S1 and S33 also need to be configured as per
the notes in arch/arm/mach-shmobile/board-mackerel.c.

A partial zImage must be written to physical partition #1 (boot)
of the eSD at sector 0 in vrl4 format. A utility vrl4 is supplied to
accomplish this.

e.g.
	vrl4 < zImage | dd of=/dev/sdX bs=512 count=17

A full copy of _the same_ zImage should be written to physical partition #1
(boot) of the eSD at sector 0. This should _not_ be in vrl4 format.

	vrl4 < zImage | dd of=/dev/sdX bs=512

Note: The commands above assume that the physical partition has been
switched. No such facility currently exists in the Linux Kernel.

Physical partitions are described in the eSD specification.  At the time of
writing they are not the same as partitions that are typically configured
using fdisk and visible through /proc/partitions