[PATCH] board: ti: j721e: README: Add documentation for eMMC boot

[Aswath Govindraju <a-govindraju@ti.com>]

Add instructions for flashing eMMC with bootloader images from SD.

Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
---
 board/ti/j721e/README | 59 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/board/ti/j721e/README b/board/ti/j721e/README
index c33afa496e7d..edb26c38ae01 100644
--- a/board/ti/j721e/README
+++ b/board/ti/j721e/README
@@ -226,6 +226,65 @@ Image formats:
                 | +-------------------+ |
                 +-----------------------+
 
+eMMC:
+-----
+ROM supports booting from eMMC from boot0 partition offset 0x0
+
+Flashing images to eMMC:
+
+The following commands can be used to download tiboot3.bin, tispl.bin,
+u-boot.img, and sysfw.itb from an SD card and write them to the eMMC boot0
+partition at respective addresses.
+
+=> mmc dev 0 1
+=> fatload mmc 1 ${loadaddr} tiboot3.bin
+=> mmc write ${loadaddr} 0x0 0x400
+=> fatload mmc 1 ${loadaddr} tispl.bin
+=> mmc write ${loadaddr} 0x400 0x1000
+=> fatload mmc 1 ${loadaddr} u-boot.img
+=> mmc write ${loadaddr} 0x1400 0x2000
+=> fatload mmc 1 ${loadaddr} sysfw.itb
+=> mmc write ${loadaddr} 0x3600 0x800
+
+To give the ROM access to the boot partition, the following command must be
+used for the first time:
+
+=> mmc partconf 0 1 1 1
+
+To set bus width, reset bus width and data rate during boot, the following
+command must be used for the first time:
+
+=> mmc bootbus 0 2 0 0
+
+To create a software partition for the rootfs, the following command can be
+used:
+
+=> gpt write mmc 0 ${partitions}
+
+eMMC layout:
+
+           boot0 partition (8 MB)                        user partition
+   0x0+----------------------------------+      0x0+-------------------------+
+      |     tiboot3.bin (512 KB)         |         |                         |
+ 0x400+----------------------------------+         |                         |
+      |       tispl.bin (2 MB)           |         |                         |
+0x1400+----------------------------------+         |        rootfs           |
+      |       u-boot.img (4 MB)          |         |                         |
+0x3400+----------------------------------+         |                         |
+      |      environment (128 KB)        |         |                         |
+0x3500+----------------------------------+         |                         |
+      |   backup environment (128 KB)    |         |                         |
+0x3600+----------------------------------+         |                         |
+      |          sysfw (1 MB)            |         |                         |
+0x3E00+----------------------------------+         +-------------------------+
+
+Kernel image and DT are expected to be present in the /boot folder of rootfs.
+To boot kernel from eMMC, use the following commands:
+
+=> setenv mmcdev 0
+=> setenv bootpart 0
+=> boot
+
 OSPI:
 -----
 ROM supports booting from OSPI from offset 0x0.
-- 
2.17.1