[coreboot-gerrit] Change in coreboot[master]: util/amdfwtool: Correct fletcher32 algorithm

[Marshall Dawson (Code Review)]

Marshall Dawson has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/34574 )

Change subject: util/amdfwtool: Correct fletcher32 algorithm
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util/amdfwtool: Correct fletcher32 algorithm

Change the fletcher32 checksum calculation to match PSP and AGESA
implementations.

The symptom of the failure has only been noted in Picasso's BIOS
Directory Table, when a BIOS binary image of different sizes were
passed to amdfwtool.  The PSP halts the boot process with the bad
BDT checksum, and if allowed to continue, AGESA asserts later due
to a failed BDT verification.

This version has been verified to produce the same result as found
at https://en.wikipedia.org/wiki/Fletcher%27s_checksum.

TEST=Build apu2, bettong, grunt and verify before/after amdfw.rom
     is unchanged.

Change-Id: I2ba2c49a70aa81c15acaab0be6b4c95e7891234f
Signed-off-by: Marshall Dawson 
---
M util/amdfwtool/amdfwtool.c
1 file changed, 7 insertions(+), 9 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/74/34574/1

diff --git a/util/amdfwtool/amdfwtool.c b/util/amdfwtool/amdfwtool.c
index 1ecb7aa..4c5b216 100644
--- a/util/amdfwtool/amdfwtool.c
+++ b/util/amdfwtool/amdfwtool.c
@@ -148,17 +148,15 @@
    c0 = 0xFFFF;
    c1 = 0xFFFF;

-	for (index = 0; index < length; index++) {
-		/*
-		* Ignore the contents of the checksum field.
-		*/
+	while (length) {
+		index = length >= 359 ? 359 : length;
+		length -= index;
+	do {
    	c0 += *(pptr++);
    	c1 += c0;
-		if ((index % 360) == 0) {
-			/* Sums[0,1] mod 64K + overflow */
-			c0 = (c0 & 0xFFFF) + (c0 >> 16);
-			c1 = (c1 & 0xFFFF) + (c1 >> 16);
-		}
+	} while (--index);
+		c0 = (c0 & 0xFFFF) + (c0 >> 16);
+		c1 = (c1 & 0xFFFF) + (c1 >> 16);
    }

/* Sums[0,1] mod 64K + overflow */