fsl-layerscape/doc/README.falcon

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4 RAM version U-Boot. Instead, it loads FIT image and boot directly to Linux.
10 booting U-Boot is not the first choice. The kernel FIT image needs to be put
14 not found, normal U-Boot flow will follow.
16 An important part of falcon boot is to prepare the device tree. A normal U-Boot
18 SPL, skipping the normal U-Boot. The device tree has to be prepared in advance.
19 A command "spl export" should be called under the normal RAM version U-Boot.
20 It is equivalent to go through "bootm" step-by-step until device tree fixup is
21 done. The device tree in memory is the one needed for falcon boot. Falcon boot
25 Linux, the device tree stored in FIT image overwrites the memory loaded by spl
29 to understand the device tree in FIT image should be the one actually used, or
31 image with embedded static device tree to multiple boards.
34 the stored sectors to. Normally this is the static device tree. The second
39 is no longer used. The static device tree is copied into this location. So
40 this macro is passed as the location of device tree when booting Linux.
42 Steps to prepare static device tree
43 -----------------------------------
44 To prepare the static device tree for Layerscape boards, it is important to
45 understand the fixups in U-Boot. Memory size and location, as well as reserved
47 microcode (if used) is embedded in the device tree. Kernel command line and
56 where the address is the location of FIT image. U-Boot goes through the booting
58 stops before "bootm go". There we have the fixed-up device tree in memory.
59 We can check the device tree header by these commands
64 Where the fdt address is the device tree in memory. It is printed by U-Boot.
65 It is useful to know the exact size. One way to extract this static device
66 tree is to save it to eMMC/SD using command in U-Boot, and extract under Linux
72 Note, U-Boot takes values as hexadecimals while Linux takes them as decimals by
74 When we have the static device tree image, we can re-make the FIT image with
76 components. Otherwise U-Boot cannot load them correctly.
78 Generate FIT image with static device tree
79 ------------------------------------------
82 /dts-v1/;
86 	#address-cells = <1>;
99 		fdt-1 {
100 			description = "Flattened Device Tree blob";
101 			data = /incbin/("./fsl-ls1043ardb-static.dtb");
119 		default = "config-1";
120 		config-1 {
123 			fdt = "fdt-1";
133 --------------------------
135 NAND boot, a RAM version full feature U-Boot is needed. Unlike SD or NAND boot,
137 separated images are used, u-boot-spl.pbl and u-boot.img. The former is SPL
138 image with RCW and PBI commands to load the SPL payload into On-Chip RAM. The
139 latter is RAM version U-Boot in FIT format (or legacy format if FIT is not
143 -----------------------
144 Falcon boot skips a lot of initialization in U-Boot. If Linux expects the
145 hardware to be initialized by U-Boot, the related code should be ported to SPL
146 build. For example, if Linux expect Ethernet PHY to be initialized in U-Boot
150 in U-Boot. Normal U-Boot sets the MDC ratio to generate a proper clock signal.