Documentation: Move firmware flashing tutorial to tutorial section

There is no need that the tutorial for flashing firmware has its own
point in the main menu. Thus, move it to the tutorial section.

Change-Id: Ife6d97254af4c006fe01480a78c76303f9cb34bb
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62424
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Thomas Heijligen <src@posteo.de>

Documentation/tutorial/flashing_firmware/index.md

@@ -0,0 +1,111 @@
+# Flashing firmware tutorial
+
+Updating the firmware is possible using the **internal method**, where the updates
+happen from a running system, or using the **external method**, where the system
+is in a shut down state and an external programmer is attached to write into the
+flash IC.
+
+## Contents
+
+* [Flashing internally](int_flashrom.md)
+* [Flashing firmware standalone](ext_standalone.md)
+* [Flashing firmware externally supplying direct power](ext_power.md)
+* [Flashing firmware externally without supplying direct power](no_ext_power.md)
+
+## General advice
+
+* It's recommended to only flash the BIOS region.
+* Always verify the firmware image.
+* If you flash externally and have transmission errors:
+  * Use short wires
+  * Reduce clock frequency
+  * Check power supply
+  * Make sure that there are no other bus masters (EC, ME, SoC, ...)
+
+## Internal method
+
+This method using [flashrom] is available on many platforms, as long as they
+aren't locked down.
+
+There are various protection schemes that make it impossible to modify or
+replace a firmware from a running system. coreboot allows to disable these
+mechanisms, making it possible to overwrite (or update) the firmware from a
+running system.
+
+Usually you must use the **external method** once to install a retrofitted
+coreboot and then you can use the **internal method** for future updates.
+
+There are multiple ways to update the firmware:
+* Using flashrom's *internal* programmer to directly write into the firmware
+  flash IC, running on the target machine itself
+* A proprietary software to update the firmware, running on the target machine
+  itself
+* A UEFI firmware update capsule
+
+More details on flashrom's
+* [internal programmer](int_flashrom.md)
+
+## External method
+
+External flashing is possible on many platforms, but requires disassembling
+the target hardware. You need to buy a flash programmer, that
+exposes the same interface as your flash IC (likely SPI).
+
+Please also have a look at the mainboard-specific documentation for details.
+
+After exposing the firmware flash IC, read the schematics and use one of the
+possible methods:
+
+* [Flashing firmware standalone](ext_standalone.md)
+* [Flashing firmware externally supplying direct power](ext_power.md)
+* [Flashing firmware externally without supplying direct power](no_ext_power.md)
+
+**WARNING:** Using the wrong method or accidentally using the wrong pinout might
+  permanently damage your hardware!
+
+**WARNING:** Do not rely on dots *painted* on flash ICs to orient the pins!
+Any dots painted on flash ICs may only indicate if they've been tested.  Dots
+that appear in datasheets to indicate pin 1 correspond to some kind of physical
+marker, such as a drilled hole, or one side being more flat than the other.
+
+## Using a layout file
+On platforms where the flash IC is shared with other components you might want
+to write only a part of the flash IC. On Intel for example there are IFD, ME and
+GBE which don't need to be updated to install coreboot.
+To make [flashrom] only write the *bios* region, leaving Intel ME and Intel IFD
+untouched, you can use a layout file, which can be created with ifdtool and a backup
+of the original firmware.
+
+```bash
+ifdtool -f rom.layout backup.rom
+```
+
+and looks similar to:
+
+```
+00000000:00000fff fd
+00500000:00bfffff bios
+00003000:004fffff me
+00001000:00002fff gbe
+```
+
+By specifying *-l* and *-i* [flashrom] writes a single region:
+```bash
+flashrom -l rom.layout -i bios -w coreboot.rom -p <programmer>
+```
+
+## Using an IFD to determine the layout
+flashrom version 1.0 supports reading the layout from the IFD (first 4KiB of
+the ROM). You don't need to manually specify a layout it, but it only works
+under the following conditions:
+
+* Only available on Intel ICH7+
+* There's only one flash IC when flashing externally
+
+```bash
+flashrom --ifd -i bios -w coreboot.rom -p <programmer>
+```
+
+**TODO** explain FMAP regions, normal/fallback mechanism, flash lock mechanisms
+
+[flashrom]: https://www.flashrom.org/Flashrom