nb/intel/haswell: Deprecate WDB params in pei_data

The WDB (Write Data Buffer) is a data region in CAR, used as a
scratchpad in the read and write training algorithms of memory
initialization. Both SNB and IVB use this buffer, but HSW does not.

Unlike earlier chipsets, Haswell contains much more in-hardware memory
training machinery, known as REUT (Robust Electrical Unified Testing).
Among other changes, the REUT hardware has a pattern storage buffer,
which renders the need for a pattern storage buffer in CAR obsolete.

Deprecate the WDB-related parameters in the pei_data structure for
Haswell, as they are leftovers from the previous generation's MRC.
Remove them from the mainboards, and explain why they are not required.

Because the MRC ABI has to remain the same, the layout of pei_data must
not be changed, so rename the WDB parameters instead of deleting them.

Tested on Asrock B85M Pro4, still boots with the MRC from Google Wolf.

Change-Id: I7acc9353a22f8c6f9fe6407617162f35849a79dd
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40406
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

1 files changed, 3 insertions, 2 deletions

diff --git a/src/northbridge/intel/haswell/pei_data.h b/src/northbridge/intel/haswell/pei_data.h
index 6e537403b3..17b7c182fa 100644
--- a/src/northbridge/intel/haswell/pei_data.h
+++ b/src/northbridge/intel/haswell/pei_data.h
@@ -73,8 +73,9 @@ struct pei_data
 	uint32_t epbar;
 	uint32_t pciexbar;
 	uint16_t smbusbar;
-	uint32_t wdbbar;
-	uint32_t wdbsize;
+	/* Unused by HSW MRC, but changes to the memory layout of this struct break the ABI */
+	uint32_t _unused_wdbbar;
+	uint32_t _unused_wdbsize;
 	uint32_t hpet_address;
 	uint32_t rcba;
 	uint32_t pmbase;