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, 22 insertions, 0 deletions

diff --git a/Documentation/flash_tutorial/no_ext_power.md b/Documentation/flash_tutorial/no_ext_power.md
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+# Flashing firmware externally supplying no power
+
+On some mainboards the flash IC's Vcc pin is connected to the internal
+power-rail, powering the entire board if the flash IC is powered externally.
+Likely it powers other chips which access the flash IC, preventing the external
+programmer from reading/writing the chip. It also violates the components'
+power sequence, bringing the ICs into an undefined state.
+
+![][flash_ic_no_diode]
+
+Please have a look at the mainboard specific documentation for details.
+
+On those boards it's recommended to use a programmer without supplying power
+externally.
+
+The key to read and write the flash IC is to put the machine into *S3* sleep-
+state or *S5* sleep-state *maybe* with Wake-On-LAN enabled.
+Another option that sometimes works is to keep the device in reset. This method requires
+knowledge of the board schematics and might require hardware modifications.
+Use a multimeter to make sure the flash IC is powered in those sleep states.
+
+[flash_ic_no_diode]: flash_ic_no_diode.svg