--- /dev/null
+.. SPDX-License-Identifier: GPL-2.0+:
+
+sf command
+==========
+
+Synopis
+-------
+
+::
+
+ sf probe [[[<bus>:]<cs>] [<hz> [<mode>]]]
+ sf read <addr> <offset>|<partition> <len>
+ sf write <addr> <offset>|<partition> <len>
+ sf erase <offset>|<partition> <len>
+ sf update <addr> <offset>|<partition> <len>
+ sf protect lock|unlock <sector> <len>
+ sf test <offset>|<partition> <len>
+
+Description
+-----------
+
+The *sf* command is used to access SPI flash, supporting read/write/erase and
+a few other functions.
+
+Probe
+-----
+
+The flash must first be probed with *sf probe* before any of the other
+subcommands can be used. All of the parameters are optional:
+
+bus
+ SPI bus number containing the SPI-flash chip, e.g. 0. If you don't know
+ the number, you can use 'dm uclass' to see all the spi devices,
+ and check the value for 'seq' for each one (here 0 and 2)::
+
+ uclass 89: spi
+ 0 spi@0 @ 05484960, seq 0
+ 1 spi@1 @ 05484b40, seq 2
+
+cs
+ SPI chip-select to use for the chip. This is often 0 and can be omitted,
+ but in some cases multiple slaves are attached to a SPI controller,
+ selected by a chip-select line for each one.
+
+hz
+ Speed of the SPI bus in hertz. This normally defaults to 100000, i.e.
+ 100KHz, which is very slow. Note that if the device exists in the
+ device tree, there might be a speed provided there, in which case this
+ setting is ignored.
+
+mode
+ SPI mode to use:
+
+ ===== ================
+ Mode Meaning
+ ===== ================
+ 0 CPOL=0, CPHA=0
+ 1 CPOL=0, CPHA=1
+ 2 CPOL=1, CPHA=0
+ 3 CPOL=1, CPHA=1
+ ===== ================
+
+ Clock phase (CPHA) 0 means that data is transferred (sampled) on the
+ first clock edge; 1 means the second.
+
+ Clock polarity (CPOL) controls the idle state of the clock, 0 for low,
+ 1 for high.
+ The active state is the opposite of idle.
+
+ You may find this `SPI documentation`_ useful.
+
+Parameters for other subcommands (described below) are as follows:
+
+addr
+ Memory address to start transfer
+
+offset
+ Flash offset to start transfer
+
+partition
+ If the parameter is not numeric, it is assumed to be a partition
+ description in the format <dev_type><dev_num>,<part_num> which is not
+ covered here. This requires CONFIG_CMD_MTDPARTS.
+
+len
+ Number of bytes to transfer
+
+Read
+~~~~
+
+Use *sf read* to read from SPI flash to memory. The read will fail if an
+attempt is made to read past the end of the flash.
+
+
+Write
+~~~~~
+
+Use *sf write* to write from memory to SPI flash. The SPI flash should be
+erased first, since otherwise the result is undefined.
+
+The write will fail if an attempt is made to read past the end of the flash.
+
+
+Erase
+~~~~~
+
+Use *sf erase* to erase a region of SPI flash. The erase will fail if any part
+of the region to be erased is protected or lies past the end of the flash. It
+may also fail if the start offset or length are not aligned to an erase region
+(e.g. 256 bytes).
+
+
+Update
+~~~~~~
+
+Use *sf update* to automatically erase and update a region of SPI flash from
+memory. This works a sector at a time (typical 4KB or 64KB). For each
+sector it first checks if the sector already has the right data. If so it is
+skipped. If not, the sector is erased and the new data written. Note that if
+the length is not a multiple of the erase size, the space after the data in
+the last sector will be erased. If the offset does not start at the beginning
+of an erase block, the operation will fail.
+
+Speed statistics are shown including the number of bytes that were already
+correct.
+
+
+Protect
+~~~~~~~
+
+SPI-flash chips often have a protection feature where the chip is split up into
+regions which can be locked or unlocked. With *sf protect* it is possible to
+change these settings, if supported by the driver.
+
+lock|unlock
+ Selects whether to lock or unlock the sectors
+
+<sector>
+ Start sector number to lock/unlock. This may be the byte offset or some
+ other value, depending on the chip.
+
+<len>
+ Number of bytes to lock/unlock
+
+
+Test
+~~~~
+
+A convenient and fast *sf test* subcommand provides a way to check that SPI
+flash is working as expected. This works in four stages:
+
+ * erase - erases the entire region
+ * check - checks that the region is erased
+ * write - writes a test pattern to the region, consisting of the U-Boot code
+ * read - reads back the test pattern to check that it was written correctly
+
+Memory is allocated for two buffers, each <len> bytes in size. At typical
+size is 64KB to 1MB. The offset and size must be aligned to an erase boundary.
+
+Note that this test will fail if any part of the SPI flash is write-protected.
+
+
+Examples
+--------
+
+This first example uses sandbox::
+
+ => sf probe
+ SF: Detected m25p16 with page size 256 Bytes, erase size 64 KiB, total 2 MiB
+ => sf read 1000 1100 80000
+ device 0 offset 0x1100, size 0x80000
+ SF: 524288 bytes @ 0x1100 Read: OK
+ => md 1000
+ 00001000: edfe0dd0 f33a0000 78000000 84250000 ......:....x..%.
+ 00001010: 28000000 11000000 10000000 00000000 ...(............
+ 00001020: 6f050000 0c250000 00000000 00000000 ...o..%.........
+ 00001030: 00000000 00000000 00000000 00000000 ................
+ 00001040: 00000000 00000000 00000000 00000000 ................
+ 00001050: 00000000 00000000 00000000 00000000 ................
+ 00001060: 00000000 00000000 00000000 00000000 ................
+ 00001070: 00000000 00000000 01000000 00000000 ................
+ 00001080: 03000000 04000000 00000000 01000000 ................
+ 00001090: 03000000 04000000 0f000000 01000000 ................
+ 000010a0: 03000000 08000000 1b000000 646e6173 ............sand
+ 000010b0: 00786f62 03000000 08000000 21000000 box............!
+ 000010c0: 646e6173 00786f62 01000000 61696c61 sandbox.....alia
+ 000010d0: 00736573 03000000 07000000 2c000000 ses............,
+ 000010e0: 6332692f 00003040 03000000 07000000 /i2c@0..........
+ 000010f0: 31000000 6963702f 00003040 03000000 ...1/pci@0......
+ => sf erase 0 80000
+ SF: 524288 bytes @ 0x0 Erased: OK
+ => sf read 1000 1100 80000
+ device 0 offset 0x1100, size 0x80000
+ SF: 524288 bytes @ 0x1100 Read: OK
+ => md 1000
+ 00001000: ffffffff ffffffff ffffffff ffffffff ................
+ 00001010: ffffffff ffffffff ffffffff ffffffff ................
+ 00001020: ffffffff ffffffff ffffffff ffffffff ................
+ 00001030: ffffffff ffffffff ffffffff ffffffff ................
+ 00001040: ffffffff ffffffff ffffffff ffffffff ................
+ 00001050: ffffffff ffffffff ffffffff ffffffff ................
+ 00001060: ffffffff ffffffff ffffffff ffffffff ................
+ 00001070: ffffffff ffffffff ffffffff ffffffff ................
+ 00001080: ffffffff ffffffff ffffffff ffffffff ................
+ 00001090: ffffffff ffffffff ffffffff ffffffff ................
+ 000010a0: ffffffff ffffffff ffffffff ffffffff ................
+ 000010b0: ffffffff ffffffff ffffffff ffffffff ................
+ 000010c0: ffffffff ffffffff ffffffff ffffffff ................
+ 000010d0: ffffffff ffffffff ffffffff ffffffff ................
+ 000010e0: ffffffff ffffffff ffffffff ffffffff ................
+ 000010f0: ffffffff ffffffff ffffffff ffffffff ................
+
+This second example is running on coral, an x86 Chromebook::
+
+ => sf probe
+ SF: Detected w25q128fw with page size 256 Bytes, erase size 4 KiB, total 16 MiB
+ => sf erase 300000 80000
+ SF: 524288 bytes @ 0x300000 Erased: OK
+ => sf update 1110000 300000 80000
+ device 0 offset 0x300000, size 0x80000
+ 524288 bytes written, 0 bytes skipped in 0.457s, speed 1164578 B/s
+
+ # This does nothing as the flash is already updated
+ => sf update 1110000 300000 80000
+ device 0 offset 0x300000, size 0x80000
+ 0 bytes written, 524288 bytes skipped in 0.196s, speed 2684354 B/s
+ => sf test 00000 80000 # try a protected region
+ SPI flash test:
+ Erase failed (err = -5)
+ Test failed
+ => sf test 800000 80000
+ SPI flash test:
+ 0 erase: 18 ticks, 28444 KiB/s 227.552 Mbps
+ 1 check: 192 ticks, 2666 KiB/s 21.328 Mbps
+ 2 write: 227 ticks, 2255 KiB/s 18.040 Mbps
+ 3 read: 189 ticks, 2708 KiB/s 21.664 Mbps
+ Test passed
+ 0 erase: 18 ticks, 28444 KiB/s 227.552 Mbps
+ 1 check: 192 ticks, 2666 KiB/s 21.328 Mbps
+ 2 write: 227 ticks, 2255 KiB/s 18.040 Mbps
+ 3 read: 189 ticks, 2708 KiB/s 21.664 Mbps
+
+
+.. _SPI documentation:
+ https://en.wikipedia.org/wiki/Serial_Peripheral_Interface
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