doc/README.rockchip - uboot-imx - Git at Google

 # SPDX-License-Identifier: GPL-2.0+
 #
 # Copyright (C) 2015 Google. Inc
 # Written by Simon Glass <sjg@chromium.org>

 U-Boot on Rockchip
 ==================

 A wide range of Rockchip SoCs are supported in mainline U-Boot


 Prerequisites
 =============

 You will need:

    - Firefly RK3288 board or something else with a supported RockChip SoC
    - Power connection to 5V using the supplied micro-USB power cable
    - Separate USB serial cable attached to your computer and the Firefly
         (connect to the micro-USB connector below the logo)
    - rkflashtool [3]
    - openssl (sudo apt-get install openssl)
    - Serial UART connection [4]
    - Suitable ARM cross compiler, e.g.:
         sudo apt-get install gcc-4.7-arm-linux-gnueabi


 Building
 ========

 At present 12 RK3288 boards are supported:

    - EVB RK3288 - use evb-rk3288 configuration
    - Fennec RK3288 - use fennec-rk3288 configuration
    - Firefly RK3288 - use firefly-rk3288 configuration
    - Hisense Chromebook - use chromebook_jerry configuration
    - Asus C100P Chromebook - use chromebook_minnie configuration
    - Asus Chromebit - use chromebook_mickey configuration
    - MiQi RK3288 - use miqi-rk3288 configuration
    - phyCORE-RK3288 RDK - use phycore-rk3288 configuration
    - PopMetal RK3288 - use popmetal-rk3288 configuration
    - Radxa Rock 2 - use rock2 configuration
    - Tinker RK3288 - use tinker-rk3288 configuration
    - Vyasa RK3288 - use vyasa-rk3288 configuration

 Two RK3036 boards are supported:

    - EVB RK3036 - use evb-rk3036 configuration
    - Kylin - use kylin_rk3036 configuration

 One RK3328 board is supported:

    - EVB RK3328

 Size RK3399 boards are supported (aarch64):

    - EBV RK3399 - use evb_rk3399 configuration
    - Firefly RK3399 - use the firefly_rk3399 configuration
    - Puma - use puma_rk3399 configuration
    - Ficus - use ficus-rk3399 configuration
    - Rock960 (Vamrs) - use rock960-rk3399 configuration
    - Bob - use chromebook_bob configuration

 Four RK3368 boards are supported:

    - Sheep - use sheep-rk3368 configuration
    - Lion - use lion-rk3368 configuration
    - Geekbox - use geekbox configuration
    - EVB PX5 - use evb-px5  configuration

 One RK3128 board is supported:

    - EVB RK3128 - use evb-rk3128 configuration

 One RK3229 board is supported:

    - EVB RK3229 - use evb-rk3229 configuration

 Two RV1108 boards are supported:

    - EVB RV1108 - use evb-rv1108 configuration
    - Elgin R1 - use elgin-rv1108 configuration

 One RV3188 baord is supported:

    - Raxda Rock - use rock configuration


 For example:

    CROSS_COMPILE=arm-linux-gnueabi- make O=firefly firefly-rk3288_defconfig all

 (or you can use another cross compiler if you prefer)


 Writing to the board with USB
 =============================

 For USB to work you must get your board into ROM boot mode, either by erasing
 your MMC or (perhaps) holding the recovery button when you boot the board.
 To erase your MMC, you can boot into Linux and type (as root)

    dd if=/dev/zero of=/dev/mmcblk0 bs=1M

 Connect your board's OTG port to your computer.

 To create a suitable image and write it to the board:

    ./firefly-rk3288/tools/mkimage -n rk3288 -T rkimage -d \
 	./firefly-rk3288/spl/u-boot-spl-dtb.bin out && \
    cat out | openssl rc4 -K 7c4e0304550509072d2c7b38170d1711 | rkflashtool l

 If all goes well you should something like:

    U-Boot SPL 2015.07-rc1-00383-ge345740-dirty (Jun 03 2015 - 10:06:49)
    Card did not respond to voltage select!
    spl: mmc init failed with error: -17
    ### ERROR ### Please RESET the board ###

 You will need to reset the board before each time you try. Yes, that's all
 it does so far. If support for the Rockchip USB protocol or DFU were added
 in SPL then we could in principle load U-Boot and boot to a prompt from USB
 as several other platforms do. However it does not seem to be possible to
 use the existing boot ROM code from SPL.


 Booting from an SD card
 =======================

 To write an image that boots from an SD card (assumed to be /dev/sdc):

    ./firefly-rk3288/tools/mkimage -n rk3288 -T rksd -d \
 	firefly-rk3288/spl/u-boot-spl-dtb.bin out && \
    sudo dd if=out of=/dev/sdc seek=64 && \
    sudo dd if=firefly-rk3288/u-boot-dtb.img of=/dev/sdc seek=16384

 This puts the Rockchip header and SPL image first and then places the U-Boot
 image at block 16384 (i.e. 8MB from the start of the SD card). This
 corresponds with this setting in U-Boot:

    #define CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR	0x4000

 Put this SD (or micro-SD) card into your board and reset it. You should see
 something like:

    U-Boot 2016.01-rc2-00309-ge5bad3b-dirty (Jan 02 2016 - 23:41:59 -0700)

    Model: Radxa Rock 2 Square
    DRAM:  2 GiB
    MMC:   dwmmc@ff0f0000: 0, dwmmc@ff0c0000: 1
    *** Warning - bad CRC, using default environment

    In:    serial
    Out:   vop@ff940000.vidconsole
    Err:   serial
    Net:   Net Initialization Skipped
    No ethernet found.
    Hit any key to stop autoboot:  0
    =>

 The rockchip bootrom can load and boot an initial spl, then continue to
 load a second-stage bootloader (ie. U-Boot) as soon as the control is returned
 to the bootrom. Both the RK3288 and the RK3036 use this special boot sequence.
 The configuration option enabling this is:

 	CONFIG_SPL_ROCKCHIP_BACK_TO_BROM=y

 You can create the image via the following operations:

    ./firefly-rk3288/tools/mkimage -n rk3288 -T rksd -d \
 	firefly-rk3288/spl/u-boot-spl-dtb.bin out && \
    cat firefly-rk3288/u-boot-dtb.bin >> out && \
    sudo dd if=out of=/dev/sdc seek=64

 If you have an HDMI cable attached you should see a video console.

 For evb_rk3036 board:
 	./evb-rk3036/tools/mkimage -n rk3036 -T rksd  -d evb-rk3036/spl/u-boot-spl.bin out && \
 	cat evb-rk3036/u-boot-dtb.bin >> out && \
 	sudo dd if=out of=/dev/sdc seek=64

 Note: rk3036 SDMMC and debug uart use the same iomux, so if you boot from SD, the
       debug uart must be disabled


 Booting from an SD card on RK3288 with TPL
 ==========================================

 Since the size of SPL can't be exceeded 0x8000 bytes in RK3288, it is not possible add
 new SPL features like Falcon mode or etc.

 So introduce TPL so-that adding new features to SPL is possible because now TPL should
 run minimal with code like DDR, clock etc and rest of new features in SPL.

 As of now TPL is added on Vyasa-RK3288 board.

 To write an image that boots from an SD card (assumed to be /dev/mmcblk0):

    ./tools/mkimage -n rk3288 -T rksd -d ./tpl/u-boot-tpl.bin out &&
     cat ./spl/u-boot-spl-dtb.bin >> out &&
     sudo dd if=out of=/dev/mmcblk0 seek=64 &&
     sudo dd if=u-boot-dtb.img of=/dev/mmcblk0 seek=16384

 Booting from an SD card on RK3188
 =================================

 For rk3188 boards the general storage onto the card stays the same as
 described above, but the image creation needs a bit more care.

 The bootrom of rk3188 expects to find a small 1kb loader which returns
 control to the bootrom, after which it will load the real loader, which
 can then be up to 29kb in size and does the regular ddr init.  This is
 handled by a single image (built as the SPL stage) that tests whether
 it is handled for the first or second time via code executed from the
 boot0-hook.

 Additionally the rk3188 requires everything the bootrom loads to be
 rc4-encrypted. Except for the very first stage the bootrom always reads
 and decodes 2kb pages, so files should be sized accordingly.

 # copy tpl, pad to 1020 bytes and append spl
 tools/mkimage -n rk3188 -T rksd -d spl/u-boot-spl.bin out

 # truncate, encode and append u-boot.bin
 truncate -s %2048 u-boot.bin
 cat u-boot.bin | split -b 512 --filter='openssl rc4 -K 7C4E0304550509072D2C7B38170D1711' >> out


 Using fastboot on rk3288
 ========================
 - Write GPT partition layout to mmc device which fastboot want to use it to
 store the image

         => gpt write mmc 1 $partitions

 - Invoke fastboot command to prepare

         => fastboot 1

 - Start fastboot request on PC

         fastboot -i 0x2207 flash loader evb-rk3288/spl/u-boot-spl-dtb.bin

 You should see something like:

         => fastboot 1
         WARNING: unknown variable: partition-type:loader
         Starting download of 357796 bytes
         ..
         downloading of 357796 bytes finished
         Flashing Raw Image
         ........ wrote 357888 bytes to 'loader'

 Booting from SPI
 ================

 To write an image that boots from SPI flash (e.g. for the Haier Chromebook or
 Bob):

    ./chromebook_jerry/tools/mkimage -n rk3288 -T rkspi \
 	-d chromebook_jerry/spl/u-boot-spl-dtb.bin spl.bin && \
    dd if=spl.bin of=spl-out.bin bs=128K conv=sync && \
    cat spl-out.bin chromebook_jerry/u-boot-dtb.img >out.bin && \
    dd if=out.bin of=out.bin.pad bs=4M conv=sync

 This converts the SPL image to the required SPI format by adding the Rockchip
 header and skipping every second 2KB block. Then the U-Boot image is written at
 offset 128KB and the whole image is padded to 4MB which is the SPI flash size.
 The position of U-Boot is controlled with this setting in U-Boot:

    #define CONFIG_SYS_SPI_U_BOOT_OFFS	(128 << 10)

 If you have a Dediprog em100pro connected then you can write the image with:

       sudo em100 -s -c GD25LQ32 -d out.bin.pad -r

 When booting you should see something like:

    U-Boot SPL 2015.07-rc2-00215-g9a58220-dirty (Jun 23 2015 - 12:11:32)


    U-Boot 2015.07-rc2-00215-g9a58220-dirty (Jun 23 2015 - 12:11:32 -0600)

    Model: Google Jerry
    DRAM:  2 GiB
    MMC:
    Using default environment

    In:    serial@ff690000
    Out:   serial@ff690000
    Err:   serial@ff690000
    =>

 Future work
 ===========

 Immediate priorities are:

 - USB host
 - USB device
 - Run CPU at full speed (code exists but we only see ~60 DMIPS maximum)
 - NAND flash
 - Boot U-Boot proper over USB OTG (at present only SPL works)


 Development Notes
 =================

 There are plenty of patches in the links below to help with this work.

 [1] https://github.com/rkchrome/uboot.git
 [2] https://github.com/linux-rockchip/u-boot-rockchip.git branch u-boot-rk3288
 [3] https://github.com/linux-rockchip/rkflashtool.git
 [4] http://wiki.t-firefly.com/index.php/Firefly-RK3288/Serial_debug/en

 rkimage
 -------

 rkimage.c produces an SPL image suitable for sending directly to the boot ROM
 over USB OTG. This is a very simple format - just the string RK32 (as 4 bytes)
 followed by u-boot-spl-dtb.bin.

 The boot ROM loads image to 0xff704000 which is in the internal SRAM. The SRAM
 starts at 0xff700000 and extends to 0xff718000 where we put the stack.

 rksd
 ----

 rksd.c produces an image consisting of 32KB of empty space, a header and
 u-boot-spl-dtb.bin. The header is defined by 'struct header0_info' although
 most of the fields are unused by U-Boot. We just need to specify the
 signature, a flag and the block offset and size of the SPL image.

 The header occupies a single block but we pad it out to 4 blocks. The header
 is encoding using RC4 with the key 7c4e0304550509072d2c7b38170d1711. The SPL
 image can be encoded too but we don't do that.

 The maximum size of u-boot-spl-dtb.bin which the boot ROM will read is 32KB,
 or 0x40 blocks. This is a severe and annoying limitation. There may be a way
 around this limitation, since there is plenty of SRAM, but at present the
 board refuses to boot if this limit is exceeded.

 The image produced is padded up to a block boundary (512 bytes). It should be
 written to the start of an SD card using dd.

 Since this image is set to load U-Boot from the SD card at block offset,
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR, dd should be used to write
 u-boot-dtb.img to the SD card at that offset. See above for instructions.

 rkspi
 -----

 rkspi.c produces an image consisting of a header and u-boot-spl-dtb.bin. The
 resulting image is then spread out so that only the first 2KB of each 4KB
 sector is used. The header is the same as with rksd and the maximum size is
 also 32KB (before spreading). The image should be written to the start of
 SPI flash.

 See above for instructions on how to write a SPI image.

 rkmux.py
 --------

 You can use this script to create #defines for SoC register access. See the
 script for usage.


 Device tree and driver model
 ----------------------------

 Where possible driver model is used to provide a structure to the
 functionality. Device tree is used for configuration. However these have an
 overhead and in SPL with a 32KB size limit some shortcuts have been taken.
 In general all Rockchip drivers should use these features, with SPL-specific
 modifications where required.

 GPT partition layout
 ----------------------------

 Rockchip use a unified GPT partition layout  in open source support.
 With this GPT partition layout, uboot can be compatilbe with other components,
 like miniloader, trusted-os, arm-trust-firmware.

 There are some documents about partitions in the links below.
 http://rockchip.wikidot.com/partitions

 --
 Simon Glass <sjg@chromium.org>
 24 June 2015
	# SPDX-License-Identifier: GPL-2.0+
	#
	# Copyright (C) 2015 Google. Inc
	# Written by Simon Glass <sjg@chromium.org>

	U-Boot on Rockchip
	==================

	A wide range of Rockchip SoCs are supported in mainline U-Boot


	Prerequisites
	=============

	You will need:

	- Firefly RK3288 board or something else with a supported RockChip SoC
	- Power connection to 5V using the supplied micro-USB power cable
	- Separate USB serial cable attached to your computer and the Firefly
	(connect to the micro-USB connector below the logo)
	- rkflashtool [3]
	- openssl (sudo apt-get install openssl)
	- Serial UART connection [4]
	- Suitable ARM cross compiler, e.g.:
	sudo apt-get install gcc-4.7-arm-linux-gnueabi


	Building
	========

	At present 12 RK3288 boards are supported:

	- EVB RK3288 - use evb-rk3288 configuration
	- Fennec RK3288 - use fennec-rk3288 configuration
	- Firefly RK3288 - use firefly-rk3288 configuration
	- Hisense Chromebook - use chromebook_jerry configuration
	- Asus C100P Chromebook - use chromebook_minnie configuration
	- Asus Chromebit - use chromebook_mickey configuration
	- MiQi RK3288 - use miqi-rk3288 configuration
	- phyCORE-RK3288 RDK - use phycore-rk3288 configuration
	- PopMetal RK3288 - use popmetal-rk3288 configuration
	- Radxa Rock 2 - use rock2 configuration
	- Tinker RK3288 - use tinker-rk3288 configuration
	- Vyasa RK3288 - use vyasa-rk3288 configuration

	Two RK3036 boards are supported:

	- EVB RK3036 - use evb-rk3036 configuration
	- Kylin - use kylin_rk3036 configuration

	One RK3328 board is supported:

	- EVB RK3328

	Size RK3399 boards are supported (aarch64):

	- EBV RK3399 - use evb_rk3399 configuration
	- Firefly RK3399 - use the firefly_rk3399 configuration
	- Puma - use puma_rk3399 configuration
	- Ficus - use ficus-rk3399 configuration
	- Rock960 (Vamrs) - use rock960-rk3399 configuration
	- Bob - use chromebook_bob configuration

	Four RK3368 boards are supported:

	- Sheep - use sheep-rk3368 configuration
	- Lion - use lion-rk3368 configuration
	- Geekbox - use geekbox configuration
	- EVB PX5 - use evb-px5 configuration

	One RK3128 board is supported:

	- EVB RK3128 - use evb-rk3128 configuration

	One RK3229 board is supported:

	- EVB RK3229 - use evb-rk3229 configuration

	Two RV1108 boards are supported:

	- EVB RV1108 - use evb-rv1108 configuration
	- Elgin R1 - use elgin-rv1108 configuration

	One RV3188 baord is supported:

	- Raxda Rock - use rock configuration


	For example:

	CROSS_COMPILE=arm-linux-gnueabi- make O=firefly firefly-rk3288_defconfig all

	(or you can use another cross compiler if you prefer)


	Writing to the board with USB
	=============================

	For USB to work you must get your board into ROM boot mode, either by erasing
	your MMC or (perhaps) holding the recovery button when you boot the board.
	To erase your MMC, you can boot into Linux and type (as root)

	dd if=/dev/zero of=/dev/mmcblk0 bs=1M

	Connect your board's OTG port to your computer.

	To create a suitable image and write it to the board:

	./firefly-rk3288/tools/mkimage -n rk3288 -T rkimage -d \
	./firefly-rk3288/spl/u-boot-spl-dtb.bin out && \
	cat out \| openssl rc4 -K 7c4e0304550509072d2c7b38170d1711 \| rkflashtool l

	If all goes well you should something like:

	U-Boot SPL 2015.07-rc1-00383-ge345740-dirty (Jun 03 2015 - 10:06:49)
	Card did not respond to voltage select!
	spl: mmc init failed with error: -17
	### ERROR ### Please RESET the board ###

	You will need to reset the board before each time you try. Yes, that's all
	it does so far. If support for the Rockchip USB protocol or DFU were added
	in SPL then we could in principle load U-Boot and boot to a prompt from USB
	as several other platforms do. However it does not seem to be possible to
	use the existing boot ROM code from SPL.


	Booting from an SD card
	=======================

	To write an image that boots from an SD card (assumed to be /dev/sdc):

	./firefly-rk3288/tools/mkimage -n rk3288 -T rksd -d \
	firefly-rk3288/spl/u-boot-spl-dtb.bin out && \
	sudo dd if=out of=/dev/sdc seek=64 && \
	sudo dd if=firefly-rk3288/u-boot-dtb.img of=/dev/sdc seek=16384

	This puts the Rockchip header and SPL image first and then places the U-Boot
	image at block 16384 (i.e. 8MB from the start of the SD card). This
	corresponds with this setting in U-Boot:

	#define CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR 0x4000

	Put this SD (or micro-SD) card into your board and reset it. You should see
	something like:

	U-Boot 2016.01-rc2-00309-ge5bad3b-dirty (Jan 02 2016 - 23:41:59 -0700)

	Model: Radxa Rock 2 Square
	DRAM: 2 GiB
	MMC: dwmmc@ff0f0000: 0, dwmmc@ff0c0000: 1
	*** Warning - bad CRC, using default environment

	In: serial
	Out: vop@ff940000.vidconsole
	Err: serial
	Net: Net Initialization Skipped
	No ethernet found.
	Hit any key to stop autoboot: 0
	=>

	The rockchip bootrom can load and boot an initial spl, then continue to
	load a second-stage bootloader (ie. U-Boot) as soon as the control is returned
	to the bootrom. Both the RK3288 and the RK3036 use this special boot sequence.
	The configuration option enabling this is:

	CONFIG_SPL_ROCKCHIP_BACK_TO_BROM=y

	You can create the image via the following operations:

	./firefly-rk3288/tools/mkimage -n rk3288 -T rksd -d \
	firefly-rk3288/spl/u-boot-spl-dtb.bin out && \
	cat firefly-rk3288/u-boot-dtb.bin >> out && \
	sudo dd if=out of=/dev/sdc seek=64

	If you have an HDMI cable attached you should see a video console.

	For evb_rk3036 board:
	./evb-rk3036/tools/mkimage -n rk3036 -T rksd -d evb-rk3036/spl/u-boot-spl.bin out && \
	cat evb-rk3036/u-boot-dtb.bin >> out && \
	sudo dd if=out of=/dev/sdc seek=64

	Note: rk3036 SDMMC and debug uart use the same iomux, so if you boot from SD, the
	debug uart must be disabled


	Booting from an SD card on RK3288 with TPL
	==========================================

	Since the size of SPL can't be exceeded 0x8000 bytes in RK3288, it is not possible add
	new SPL features like Falcon mode or etc.

	So introduce TPL so-that adding new features to SPL is possible because now TPL should
	run minimal with code like DDR, clock etc and rest of new features in SPL.

	As of now TPL is added on Vyasa-RK3288 board.

	To write an image that boots from an SD card (assumed to be /dev/mmcblk0):

	./tools/mkimage -n rk3288 -T rksd -d ./tpl/u-boot-tpl.bin out &&
	cat ./spl/u-boot-spl-dtb.bin >> out &&
	sudo dd if=out of=/dev/mmcblk0 seek=64 &&
	sudo dd if=u-boot-dtb.img of=/dev/mmcblk0 seek=16384

	Booting from an SD card on RK3188
	=================================

	For rk3188 boards the general storage onto the card stays the same as
	described above, but the image creation needs a bit more care.

	The bootrom of rk3188 expects to find a small 1kb loader which returns
	control to the bootrom, after which it will load the real loader, which
	can then be up to 29kb in size and does the regular ddr init. This is
	handled by a single image (built as the SPL stage) that tests whether
	it is handled for the first or second time via code executed from the
	boot0-hook.

	Additionally the rk3188 requires everything the bootrom loads to be
	rc4-encrypted. Except for the very first stage the bootrom always reads
	and decodes 2kb pages, so files should be sized accordingly.

	# copy tpl, pad to 1020 bytes and append spl
	tools/mkimage -n rk3188 -T rksd -d spl/u-boot-spl.bin out

	# truncate, encode and append u-boot.bin
	truncate -s %2048 u-boot.bin
	cat u-boot.bin \| split -b 512 --filter='openssl rc4 -K 7C4E0304550509072D2C7B38170D1711' >> out


	Using fastboot on rk3288
	========================
	- Write GPT partition layout to mmc device which fastboot want to use it to
	store the image

	=> gpt write mmc 1 $partitions

	- Invoke fastboot command to prepare

	=> fastboot 1

	- Start fastboot request on PC

	fastboot -i 0x2207 flash loader evb-rk3288/spl/u-boot-spl-dtb.bin

	You should see something like:

	=> fastboot 1
	WARNING: unknown variable: partition-type:loader
	Starting download of 357796 bytes
	..
	downloading of 357796 bytes finished
	Flashing Raw Image
	........ wrote 357888 bytes to 'loader'

	Booting from SPI
	================

	To write an image that boots from SPI flash (e.g. for the Haier Chromebook or
	Bob):

	./chromebook_jerry/tools/mkimage -n rk3288 -T rkspi \
	-d chromebook_jerry/spl/u-boot-spl-dtb.bin spl.bin && \
	dd if=spl.bin of=spl-out.bin bs=128K conv=sync && \
	cat spl-out.bin chromebook_jerry/u-boot-dtb.img >out.bin && \
	dd if=out.bin of=out.bin.pad bs=4M conv=sync

	This converts the SPL image to the required SPI format by adding the Rockchip
	header and skipping every second 2KB block. Then the U-Boot image is written at
	offset 128KB and the whole image is padded to 4MB which is the SPI flash size.
	The position of U-Boot is controlled with this setting in U-Boot:

	#define CONFIG_SYS_SPI_U_BOOT_OFFS (128 << 10)

	If you have a Dediprog em100pro connected then you can write the image with:

	sudo em100 -s -c GD25LQ32 -d out.bin.pad -r

	When booting you should see something like:

	U-Boot SPL 2015.07-rc2-00215-g9a58220-dirty (Jun 23 2015 - 12:11:32)


	U-Boot 2015.07-rc2-00215-g9a58220-dirty (Jun 23 2015 - 12:11:32 -0600)

	Model: Google Jerry
	DRAM: 2 GiB
	MMC:
	Using default environment

	In: serial@ff690000
	Out: serial@ff690000
	Err: serial@ff690000
	=>

	Future work
	===========

	Immediate priorities are:

	- USB host
	- USB device
	- Run CPU at full speed (code exists but we only see ~60 DMIPS maximum)
	- NAND flash
	- Boot U-Boot proper over USB OTG (at present only SPL works)


	Development Notes
	=================

	There are plenty of patches in the links below to help with this work.

	[1] https://github.com/rkchrome/uboot.git
	[2] https://github.com/linux-rockchip/u-boot-rockchip.git branch u-boot-rk3288
	[3] https://github.com/linux-rockchip/rkflashtool.git
	[4] http://wiki.t-firefly.com/index.php/Firefly-RK3288/Serial_debug/en

	rkimage
	-------

	rkimage.c produces an SPL image suitable for sending directly to the boot ROM
	over USB OTG. This is a very simple format - just the string RK32 (as 4 bytes)
	followed by u-boot-spl-dtb.bin.

	The boot ROM loads image to 0xff704000 which is in the internal SRAM. The SRAM
	starts at 0xff700000 and extends to 0xff718000 where we put the stack.

	rksd
	----

	rksd.c produces an image consisting of 32KB of empty space, a header and
	u-boot-spl-dtb.bin. The header is defined by 'struct header0_info' although
	most of the fields are unused by U-Boot. We just need to specify the
	signature, a flag and the block offset and size of the SPL image.

	The header occupies a single block but we pad it out to 4 blocks. The header
	is encoding using RC4 with the key 7c4e0304550509072d2c7b38170d1711. The SPL
	image can be encoded too but we don't do that.

	The maximum size of u-boot-spl-dtb.bin which the boot ROM will read is 32KB,
	or 0x40 blocks. This is a severe and annoying limitation. There may be a way
	around this limitation, since there is plenty of SRAM, but at present the
	board refuses to boot if this limit is exceeded.

	The image produced is padded up to a block boundary (512 bytes). It should be
	written to the start of an SD card using dd.

	Since this image is set to load U-Boot from the SD card at block offset,
	CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR, dd should be used to write
	u-boot-dtb.img to the SD card at that offset. See above for instructions.

	rkspi
	-----

	rkspi.c produces an image consisting of a header and u-boot-spl-dtb.bin. The
	resulting image is then spread out so that only the first 2KB of each 4KB
	sector is used. The header is the same as with rksd and the maximum size is
	also 32KB (before spreading). The image should be written to the start of
	SPI flash.

	See above for instructions on how to write a SPI image.

	rkmux.py
	--------

	You can use this script to create #defines for SoC register access. See the
	script for usage.


	Device tree and driver model
	----------------------------

	Where possible driver model is used to provide a structure to the
	functionality. Device tree is used for configuration. However these have an
	overhead and in SPL with a 32KB size limit some shortcuts have been taken.
	In general all Rockchip drivers should use these features, with SPL-specific
	modifications where required.

	GPT partition layout
	----------------------------

	Rockchip use a unified GPT partition layout in open source support.
	With this GPT partition layout, uboot can be compatilbe with other components,
	like miniloader, trusted-os, arm-trust-firmware.

	There are some documents about partitions in the links below.
	http://rockchip.wikidot.com/partitions

	--
	Simon Glass <sjg@chromium.org>
	24 June 2015