sbxxx: Handle active IMCs in AMD chipsets

Detect and temporarily disable the IMC while accessing the flash.
Disable writes on default, but allow the user to enforce it.

Corresponding to flashrom svn r1704.

Signed-off-by: Rudolf Marek <r.marek@assembler.cz>
Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: David Hendricks <dhendrix@google.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/flashrom.8 b/flashrom.8
index b8fd391..dccfd1a 100644
--- a/flashrom.8
+++ b/flashrom.8
@@ -329,6 +329,23 @@ flashrom doesn't detect an active IT87 LPC<->SPI bridge, please send a bug
 report so we can diagnose the problem.
 .sp
 .TP
+.B AMD chipsets
+.sp
+Beginning with the SB700 chipset there is an integrated microcontroller (IMC) based on the 8051 embedded in
+every AMD southbridge. Its firmware resides in the same flash chip as the host's which makes writing to the
+flash risky if the IMC is active. Flashrom tries to temporarily disable the IMC but even then changing the
+contents of the flash can have unwanted effects: when the IMC continues (at the latest after a reboot) it will
+continue executing code from the flash. If the code was removed or changed in an unfortunate way it is
+unpredictable what the IMC will do. Therefore, if flashrom detects an active IMC it will disable write support
+unless the user forces it with the
+.sp
+.B "  flashrom \-p internal:amd_imc_force=yes"
+.sp
+syntax. The user is responsible for supplying a suitable image or leaving out the IMC region with the help of
+a layout file. This limitation might be removed in the future when we understand the details better and have
+received enough feedback from users. Please report the outcome if you had to use this option to write a chip.
+.sp
+.TP
 .B Intel chipsets
 .sp
 If you have an Intel chipset with an ICH8 or later southbridge with SPI flash