Edward O'Callaghan has uploaded this change for review.

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flashrom.c: Rewrite prepare_chip_access() 4BA enablement

Factor out the 4BA enablement logic into its own function and
break down predicates into a series of easy to follow base-cases
complete with comments.

TEST=`$ sudo ./flashrom -p internal -r /tmp/bios`.
on a Found chipset "Intel Tiger Lake U Premium".

Change-Id: I10a426331cb2a3485e3dd786fa771e20870cbd84
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
---
M flashrom.c
1 file changed, 57 insertions(+), 24 deletions(-)

git pull ssh://review.coreboot.org:29418/flashrom refs/changes/42/71742/1

diff --git a/flashrom.c b/flashrom.c
index 822594b..f7499c3 100644
--- a/flashrom.c
+++ b/flashrom.c
@@ -1905,6 +1905,45 @@
 	return 0;
 }
 
+static int enable_4ba_if_required(struct flashctx *const flash)
+{
+	/* Check if chip too small to need 4BA. */
+	if (flash->chip->total_size <= 16 * 1024) {
+		return 0;
+	}
+
+	/* Check if SPI bus with 4BA enabled has a SPI master missing 4BA mode. */
+	if (!spi_master_no_4ba_modes(flash)) {
+		return 0;
+	}
+
+	/* Check if SPI bus with 4BA has a SPI master that supports a 4BA mode. */
+	if (!spi_master_4ba(flash)) {
+		msg_cerr("Programmer doesn't support this chip. Aborting.\n");
+		return 1;
+	}
+
+	/* Check chip supports native 4BA instructions and if not bail out. */
+	if ((flash->chip->feature_bits & FEATURE_4BA_NATIVE) != FEATURE_4BA_NATIVE) {
+		msg_cerr("Chip does not support 4BA Native instructions. Aborting.\n");
+		return 1;
+	}
+
+	/* Check if chip is on a chipbus that supports 4BA addressing mode. */
+	if (!spi_chip_4ba(flash)) {
+		return 0;
+	}
+
+	/* Enable/disable 4-byte addressing mode. */
+	int ret = spi_master_4ba(flash) ? spi_enter_4ba(flash): spi_exit_4ba(flash);
+	if (ret) {
+		msg_cerr("Failed to set correct 4BA mode! Aborting.\n");
+		return 1;
+	}
+
+	return 0;
+}
+
 int prepare_flash_access(struct flashctx *const flash,
 			 const bool read_it, const bool write_it,
 			 const bool erase_it, const bool verify_it)
@@ -1933,30 +1972,7 @@
 	flash->address_high_byte = -1;
 	flash->in_4ba_mode = false;
 
-	/* Be careful about 4BA chips and broken masters */
-	if (flash->chip->total_size > 16 * 1024 && spi_master_no_4ba_modes(flash)) {
-		/* If we can't use native instructions, bail out */
-		if ((flash->chip->feature_bits & FEATURE_4BA_NATIVE) != FEATURE_4BA_NATIVE
-		    || !spi_master_4ba(flash)) {
-			msg_cerr("Programmer doesn't support this chip. Aborting.\n");
-			return 1;
-		}
-	}
-
-	/* Enable/disable 4-byte addressing mode if flash chip supports it */
-	if (spi_chip_4ba(flash)) {
-		int ret;
-		if (spi_master_4ba(flash))
-			ret = spi_enter_4ba(flash);
-		else
-			ret = spi_exit_4ba(flash);
-		if (ret) {
-			msg_cerr("Failed to set correct 4BA mode! Aborting.\n");
-			return 1;
-		}
-	}
-
-	return 0;
+	return enable_4ba_if_required(flash);
 }
 
 void finalize_flash_access(struct flashctx *const flash)

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