xref: /openbmc/u-boot/doc/README.ubispl (revision 390194d4)
1Lightweight UBI and UBI fastmap support
2
3# Copyright (C) Thomas Gleixner <tglx@linutronix.de>
4#
5# SPDX-License-Identifier: GPL 2.0+ BSD-3-Clause
6
7Scans the UBI information and loads the requested static volumes into
8memory.
9
10Configuration Options:
11
12   CONFIG_SPL_UBI
13     Enables the SPL UBI support
14
15   CONFIG_SPL_UBI_MAX_VOL_LEBS
16     The maximum number of logical eraseblocks which a static volume
17     to load can contain. Used for sizing the scan data structure
18
19   CONFIG_SPL_UBI_MAX_PEB_SIZE
20     The maximum physical erase block size. Either a compile time
21     constant or runtime detection. Used for sizing the scan data
22     structure
23
24   CONFIG_SPL_UBI_MAX_PEBS
25     The maximum physical erase block count. Either a compile time
26     constant or runtime detection. Used for sizing the scan data
27     structure
28
29   CONFIG_SPL_UBI_VOL_IDS
30     The maximum volume ids which can be loaded. Used for sizing the
31     scan data structure.
32
33Usage notes:
34
35In the board config file define for example:
36
37#define CONFIG_SPL_UBI
38#define CONFIG_SPL_UBI_MAX_VOL_LEBS	256
39#define CONFIG_SPL_UBI_MAX_PEB_SIZE	(256*1024)
40#define CONFIG_SPL_UBI_MAX_PEBS		4096
41#define CONFIG_SPL_UBI_VOL_IDS		8
42
43The size requirement is roughly as follows:
44
45    2k for the basic data structure
46  + CONFIG_SPL_UBI_VOL_IDS * CONFIG_SPL_UBI_MAX_VOL_LEBS * 8
47  + CONFIG_SPL_UBI_MAX_PEBS * 64
48  + CONFIG_SPL_UBI_MAX_PEB_SIZE * UBI_FM_MAX_BLOCKS
49
50The last one is big, but I really don't care in that stage. Real world
51implementations only use the first couple of blocks, but the code
52handles up to UBI_FM_MAX_BLOCKS.
53
54Given the above configuration example the requirement is about 5M
55which is usually not a problem to reserve in the RAM along with the
56other areas like the kernel/dts load address.
57
58So something like this will do the trick:
59
60#define SPL_FINFO_ADDR			0x80800000
61#define SPL_DTB_LOAD_ADDR		0x81800000
62#define SPL_KERNEL_LOAD_ADDR		0x82000000
63
64In the board file, implement the following:
65
66static struct ubispl_load myvolumes[] = {
67	{
68		.vol_id		= 0,	/* kernel volume */
69		.load_addr	= (void *)SPL_KERNEL_LOAD_ADDR,
70	},
71	{
72		.vol_id		= 1,	/* DT blob */
73		.load_addr	= (void *)SPL_DTB_LOAD_ADDR,
74	}
75};
76
77int spl_start_uboot(void)
78{
79	struct ubispl_info info;
80
81	info.ubi = (struct ubi_scan_info *) SPL_FINFO_ADDR;
82	info.fastmap = 1;
83	info.read = nand_spl_read_flash;
84
85#if COMPILE_TIME_DEFINED
86	/*
87	 * MY_NAND_NR_SPL_PEBS is the number of physical erase blocks
88	 * in the FLASH which are reserved for the SPL. Think about
89	 * mtd partitions:
90	 *
91	 * part_spl { .start = 0, .end = 4 }
92	 * part_ubi { .start = 4, .end = NR_PEBS }
93	 */
94	info.peb_offset = MY_NAND_NR_SPL_PEBS;
95	info.peb_size = CONFIG_SYS_NAND_BLOCK_SIZE;
96	info.vid_offset = MY_NAND_UBI_VID_OFFS;
97	info.leb_start = MY_NAND_UBI_DATA_OFFS;
98	info.peb_count = MY_NAND_UBI_NUM_PEBS;
99#else
100	get_flash_info(&flash_info);
101	info.peb_offset = MY_NAND_NR_SPL_PEBS;
102	info.peb_size = flash_info.peb_size;
103
104	/*
105	 * The VID and Data offset depend on the capability of the
106	 * FLASH chip to do subpage writes.
107	 *
108	 * If the flash chip supports subpage writes, then the VID
109	 * header starts at the second subpage. So for 2k pages size
110	 * with 4 subpages the VID offset is 512. The DATA offset is 2k.
111	 *
112	 * If the flash chip does not support subpage writes then the
113	 * VID offset is FLASH_PAGE_SIZE and the DATA offset
114	 * 2 * FLASH_PAGE_SIZE
115	 */
116	info.vid_offset = flash_info.vid_offset;
117	info.leb_start = flash_info.data_offset;
118
119	/*
120	 * The flash reports the total number of erase blocks, so
121	 * we need to subtract the number of blocks which are reserved
122	 * for the SPL itself and not managed by UBI.
123	 */
124	info.peb_count = flash_info.peb_count - MY_NAND_NR_SPL_PEBS;
125#endif
126
127	ret = ubispl_load_volumes(&info, myvolumes, ARRAY_SIZE(myvolumes);
128
129	....
130
131}
132
133Note: you can load any payload that way. You can even load u-boot from
134UBI, so the only non UBI managed FLASH area is the one which is
135reserved for the SPL itself and read from the SoC ROM.
136
137And you can do fallback scenarios:
138
139    if (ubispl_load_volumes(&info, volumes0, ARRAY_SIZE(volumes0)))
140        if (ubispl_load_volumes(&info, volumes1, ARRAY_SIZE(volumes1)))
141	    ubispl_load_volumes(&info, vol_uboot, ARRAY_SIZE(vol_uboot));
142