Change in ...coreboot[master]: ec/chromeec: fix LPC read/write for MEC devices

[Matt DeVillier (Code Review)]

Matt DeVillier has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/30444

Change subject: ec/chromeec: fix LPC read/write for MEC devices
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ec/chromeec: fix LPC read/write for MEC devices

Commit 8cf8aa2 [ec/google/chromeec: Use common MEC interface]
changed the return mechanism for the checksum on reads/writes
for MEC devices, but incorrectly handled the passed-in csum
parameter by not dereferencing. This led to the returned csum
value always being zero, which causes all EC commands with non-
NULL data_in to fail with a checksum error.

Fix this by storing the returned checksum in a temp variable,
and only assigning to csum when the pointer isn't NULL;

Test: build/boot google/chell, verify EC hello command succeeds,
keyboard backlight turned on at boot.

Change-Id: I7122c3fdc5a19f87f12975ee448728cf29948436
Signed-off-by: Matt DeVillier 
---
M src/ec/google/chromeec/ec_lpc.c
1 file changed, 6 insertions(+), 2 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/44/30444/1

diff --git a/src/ec/google/chromeec/ec_lpc.c b/src/ec/google/chromeec/ec_lpc.c
index c8665c9..61005d3 100644
--- a/src/ec/google/chromeec/ec_lpc.c
+++ b/src/ec/google/chromeec/ec_lpc.c
@@ -41,9 +41,11 @@
 #if IS_ENABLED(CONFIG_EC_GOOGLE_CHROMEEC_MEC)
    /* Access desired range though EMI interface */
    if (port >= MEC_EMI_RANGE_START && port <= MEC_EMI_RANGE_END) {
-		csum += mec_io_bytes(MEC_IO_READ, MEC_EMI_BASE,
+		u8 ret = mec_io_bytes(MEC_IO_READ, MEC_EMI_BASE,
    			     port - MEC_EMI_RANGE_START,
    			     dest, length);
+		if (csum)
+			*csum += ret;
    	return;
    }
 #endif
@@ -78,9 +80,11 @@
 #if IS_ENABLED(CONFIG_EC_GOOGLE_CHROMEEC_MEC)
    /* Access desired range though EMI interface */
    if (port >= MEC_EMI_RANGE_START && port <= MEC_EMI_RANGE_END) {
-		csum += mec_io_bytes(MEC_IO_WRITE, MEC_EMI_BASE,
+		u8 ret = mec_io_bytes(MEC_IO_WRITE, MEC_EMI_BASE,
    			     port - MEC_EMI_RANGE_START,
    			     msg, length);
+		if (csum)
+			*csum += ret;
    	return;
    }
 #endif