mb/google/zork/variants/dalboz: Use HS200 for eMMC

Earlier versions of Dalboz did not correctly handle HS400. One fix was
to add stitching vias, but these boards did not have them. b/156539551

Another possible fix is to add tuning parameters including drive
strength, but that is still a WIP. b/158959725

This should correct OS load failures in the meantime by running the bus
slower.

BUG=b:158845662
TEST=build, flash, boot sku 0x5a80000c to OS
BRANCH=None
Signed-off-by: Eric Peers <epeers@google.com>
Change-Id: Ia3e7a641bde04c5a7be29bf91c38dd8c110ed17a
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43572
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/zork/variants/dalboz/variant.c

@@ -127,9 +127,21 @@ void variant_devtree_update(void)
 	cfg = config_of_soc();
 
 	if (sku_has_emmc()) {
-		if (sku_id() == 0x5A800003)
+		if ((sku_id() == 0x5A800003) || (sku_id() == 0x5A80000C)) {
-			/* rev0 boards have issues with HS400 */
+			/*
+			 * rev0 and rev1 boards have issues with HS400
+			 *
+			 * There is a tuning fix with ES which shows promise
+			 * for some boards, and a HW fix with stitching vias.
+			 * There were also concerns that these boards did not
+			 * have good margins for certain skus.
+			 *
+			 * But these original boards have none of these fixes.
+			 * So we keep the speed low here, with the intent that
+			 * other variants implement these corrections.
+			 */
 			cfg->sd_emmc_config = SD_EMMC_EMMC_HS200;
+		}
 	} else {
 		cfg->sd_emmc_config = SD_EMMC_DISABLE;
 	}