Documentation: Add basic flashing tutorial for Lenovo

* Add basic flashing tutorial
** Describe internal and external flashing
** Describe flash supply diode protection
** Gives general advices on flashing
** Describe how to use flashrom --ifd
*  Describe basic flashing on Lenovo T4xx devices
** Describe how to disassemble and access the flash IC on T4xx
** Describe flash layout on Sandy Bridge and Ivy Bridge series.

Change-Id: Ia833e27f4e7d89ee32be9bed21a0c021839facec
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/27852
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/Documentation/mainboard/lenovo/xx20_series.md b/Documentation/mainboard/lenovo/xx20_series.md
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+# Lenovo Sandy Bridge series
+
+## Flashing coreboot
+```eval_rst
++---------------------+--------------------+
+| Type                | Value              |
++=====================+====================+
+| Socketed flash      | no                 |
++---------------------+--------------------+
+| Size                | 8 MiB              |
++---------------------+--------------------+
+| In circuit flashing | Yes                |
++---------------------+--------------------+
+| Package             | SOIC-8             |
++---------------------+--------------------+
+| Write protection    | No                 |
++---------------------+--------------------+
+| Dual BIOS feature   | No                 |
++---------------------+--------------------+
+| Internal flashing   | Yes                |
++---------------------+--------------------+
+```
+
+## Installation instructions
+* Update the EC firmware, as there's no support for EC updates in coreboot.
+* Do **NOT** accidently swap pins or power on the board while a SPI flasher
+  is connected. It will destroy your device.
+* It's recommended to only flash the BIOS region. In that case you don't
+  need to extract BLOBs from vendor firmware.
+  If you want to flash the whole chip, you need BLOBs when building
+  coreboot.
+* The shipped *Flash layout* allocates 3MiB to the BIOS region, which is the space
+  usable by coreboot.
+* ROM chip size should be set to 8MiB.
+
+```eval_rst
+Please also have a look at :doc:`../../flash_tutorial/index`.
+```
+
+## Flash layout
+There's one 8MiB flash which contains IFD, GBE, ME and BIOS regions.
+On Lenovo's UEFI the EC firmware update is placed at the start of the BIOS
+region. The update is then written into the EC once.
+
+![][fl]
+
+[fl]: flashlayout_xx20.svg
+