diff --git a/82802ab.c b/82802ab.c
index 2600642..57b3363 100644
--- a/82802ab.c
+++ b/82802ab.c
@@ -160,6 +160,7 @@
 	return 0;
 }
 
+/* chunksize is 1 */
 int write_82802ab(struct flashchip *flash, uint8_t *buf)
 {
 	return write_page_82802ab(flash, buf, 0, flash->total_size * 1024);
diff --git a/chipdrivers.h b/chipdrivers.h
index f19e991..ad2f89d 100644
--- a/chipdrivers.h
+++ b/chipdrivers.h
@@ -86,8 +86,8 @@
 int erase_sector_jedec(struct flashchip *flash, unsigned int page, unsigned int pagesize);
 int erase_block_jedec(struct flashchip *flash, unsigned int page, unsigned int blocksize);
 int erase_chip_block_jedec(struct flashchip *flash, unsigned int page, unsigned int blocksize);
-int write_sector_jedec_common(struct flashchip *flash, uint8_t *src, int start, int len, unsigned int mask);
-int write_page_write_jedec_common(struct flashchip *flash, uint8_t *src, int start, int page_size, unsigned int mask);
+int write_sector_jedec_common(struct flashchip *flash, uint8_t *src, int start, int len);
+int write_page_write_jedec_common(struct flashchip *flash, uint8_t *src, int start, int page_size);
 
 /* m29f400bt.c */
 int probe_m29f400bt(struct flashchip *flash);
@@ -106,10 +106,11 @@
 int erase_sector_28sf040(struct flashchip *flash, unsigned int address, unsigned int sector_size);
 int write_28sf040(struct flashchip *flash, uint8_t *buf);
 int write_sector_28sf040(struct flashchip *flash, uint8_t *src, int start, int len);
+int unprotect_28sf040(struct flashchip *flash);
+int protect_28sf040(struct flashchip *flash);
 
 /* sst49lfxxxc.c */
 int erase_sector_49lfxxxc(struct flashchip *flash, unsigned int address, unsigned int sector_size);
-int write_49lfxxxc(struct flashchip *flash, uint8_t *buf);
 int unlock_49lfxxxc(struct flashchip *flash);
 
 /* sst_fwhub.c */
diff --git a/flashchips.c b/flashchips.c
index d1e4a99..715c054 100644
--- a/flashchips.c
+++ b/flashchips.c
@@ -2995,7 +2995,7 @@
 		.total_size	= 512,
 		.page_size	= 64 * 1024,
 		.feature_bits	= FEATURE_ADDR_SHIFTED | FEATURE_EITHER_RESET,
-		.tested		= TEST_BAD_WRITE, /* Implicit eraseblock layout in write_m29f400bt is broken. */
+		.tested		= TEST_UNTESTED,
 		.probe		= probe_m29f400bt,
 		.probe_timing	= TIMING_IGNORED, /* routine don't use probe_timing (m29f400bt.c) */
 		.block_erasers	=
@@ -3013,7 +3013,7 @@
 				.block_erase = block_erase_chip_m29f400bt,
 			},
 		},
-		.write		= NULL,
+		.write		= write_m29f400bt,
 		.read		= read_memmapped,
 	},
 
@@ -5107,6 +5107,7 @@
 				.block_erase = erase_chip_28sf040,
 			}
 		},
+		.unlock		= unprotect_28sf040,
 		.write		= write_28sf040,
 		.read		= read_memmapped,
 	},
@@ -5564,7 +5565,7 @@
 			}
 		},
 		.unlock		= unlock_49lfxxxc,
-		.write		= write_49lfxxxc,
+		.write		= write_82802ab,
 		.read		= read_memmapped,
 	},
 
@@ -5627,7 +5628,7 @@
 			}
 		},
 		.unlock		= unlock_49lfxxxc,
-		.write		= write_49lfxxxc,
+		.write		= write_82802ab,
 		.read		= read_memmapped,
 	},
 
@@ -5659,7 +5660,7 @@
 			}
 		},
 		.unlock		= unlock_49lfxxxc,
-		.write		= write_49lfxxxc,
+		.write		= write_82802ab,
 		.read		= read_memmapped,
 	},
 
@@ -5837,7 +5838,7 @@
 			}
 		},
 		.unlock		= unlock_49lfxxxc,
-		.write		= write_49lfxxxc,
+		.write		= write_82802ab,
 		.read		= read_memmapped,
 	},
 
@@ -6315,7 +6316,7 @@
 		.total_size	= 512,
 		.page_size	= 64 * 1024,
 		.feature_bits	= FEATURE_ADDR_SHIFTED | FEATURE_EITHER_RESET,
-		.tested		= TEST_BAD_WRITE, /* Implicit eraseblock layout in write_m29f400bt is broken. */
+		.tested		= TEST_UNTESTED,
 		.probe		= probe_m29f400bt,
 		.probe_timing	= TIMING_IGNORED, /* routine doesn't use probe_timing (m29f400bt.c) */
 		.block_erasers	=
@@ -6333,7 +6334,7 @@
 				.block_erase = block_erase_chip_m29f400bt,
 			}
 		},
-		.write		= NULL,
+		.write		= write_m29f400bt,
 		.read		= read_memmapped,
 	},
 	{
diff --git a/jedec.c b/jedec.c
index 6146fc4..259f883 100644
--- a/jedec.c
+++ b/jedec.c
@@ -92,6 +92,25 @@
 		msg_cdbg("%s: excessive loops, i=0x%x\n", __func__, i);
 }
 
+static int getaddrmask(struct flashchip *flash)
+{
+	switch (flash->feature_bits & FEATURE_ADDR_MASK) {
+	case FEATURE_ADDR_FULL:
+		return MASK_FULL;
+		break;
+	case FEATURE_ADDR_2AA:
+		return MASK_2AA;
+		break;
+	case FEATURE_ADDR_AAA:
+		return MASK_AAA;
+		break;
+	default:
+		msg_cerr("%s called with unknown mask\n", __func__);
+		return 0;
+		break;
+	}
+}
+
 static void start_program_jedec_common(struct flashchip *flash, unsigned int mask)
 {
 	chipaddr bios = flash->virtual_memory;
@@ -317,11 +336,14 @@
 	return failed;
 }
 
-int write_sector_jedec_common(struct flashchip *flash, uint8_t *src, int start, int len, unsigned int mask)
+int write_sector_jedec_common(struct flashchip *flash, uint8_t *src, int start, int len)
 {
 	int i, failed = 0;
 	chipaddr dst = flash->virtual_memory + start;
 	chipaddr olddst;
+	int mask;
+
+	mask = getaddrmask(flash);
 
 	olddst = dst;
 	for (i = 0; i < len; i++) {
@@ -335,13 +357,16 @@
 	return failed;
 }
 
-int write_page_write_jedec_common(struct flashchip *flash, uint8_t *src, int start, int page_size, unsigned int mask)
+int write_page_write_jedec_common(struct flashchip *flash, uint8_t *src, int start, int page_size)
 {
 	int i, tried = 0, failed;
 	uint8_t *s = src;
 	chipaddr bios = flash->virtual_memory;
 	chipaddr dst = bios + start;
 	chipaddr d = dst;
+	int mask;
+
+	mask = getaddrmask(flash);
 
 retry:
 	/* Issue JEDEC Start Program command */
@@ -373,49 +398,55 @@
 	return failed;
 }
 
-static int getaddrmask(struct flashchip *flash)
+/*
+ * Write a part of the flash chip.
+ * FIXME: Use the chunk code from Michael Karcher instead.
+ * This function is a slightly modified copy of spi_write_chunked.
+ * Each page is written separately in chunks with a maximum size of chunksize.
+ */
+int write_jedec_pages(struct flashchip *flash, uint8_t *buf, int start, int len)
 {
-	switch (flash->feature_bits & FEATURE_ADDR_MASK) {
-	case FEATURE_ADDR_FULL:
-		return MASK_FULL;
-		break;
-	case FEATURE_ADDR_2AA:
-		return MASK_2AA;
-		break;
-	case FEATURE_ADDR_AAA:
-		return MASK_AAA;
-		break;
-	default:
-		msg_cerr("%s called with unknown mask\n", __func__);
-		return 0;
-		break;
-	}
-}
-
-int write_jedec(struct flashchip *flash, uint8_t *buf)
-{
-	int mask;
-	int i, failed = 0;
-	int total_size = flash->total_size * 1024;
+	int i, starthere, lenhere;
+	/* FIXME: page_size is the wrong variable. We need max_writechunk_size
+	 * in struct flashchip to do this properly. All chips using
+	 * write_jedec have page_size set to max_writechunk_size, so
+	 * we're OK for now.
+	 */
 	int page_size = flash->page_size;
 
-	mask = getaddrmask(flash);
+	/* Warning: This loop has a very unusual condition and body.
+	 * The loop needs to go through each page with at least one affected
+	 * byte. The lowest page number is (start / page_size) since that
+	 * division rounds down. The highest page number we want is the page
+	 * where the last byte of the range lives. That last byte has the
+	 * address (start + len - 1), thus the highest page number is
+	 * (start + len - 1) / page_size. Since we want to include that last
+	 * page as well, the loop condition uses <=.
+	 */
+	for (i = start / page_size; i <= (start + len - 1) / page_size; i++) {
+		/* Byte position of the first byte in the range in this page. */
+		/* starthere is an offset to the base address of the chip. */
+		starthere = max(start, i * page_size);
+		/* Length of bytes in the range in this page. */
+		lenhere = min(start + len, (i + 1) * page_size) - starthere;
 
-	for (i = 0; i < total_size / page_size; i++) {
-		if (write_page_write_jedec_common(flash, buf + i * page_size, i * page_size, page_size, mask))
-			failed = 1;
+		if (write_page_write_jedec_common(flash, buf + starthere - start, starthere, lenhere))
+			return 1;
 	}
 
-	return failed;
+	return 0;
 }
 
+/* chunksize is page_size */
+int write_jedec(struct flashchip *flash, uint8_t *buf)
+{
+	return write_jedec_pages(flash, buf, 0, flash->total_size * 1024);
+}
+
+/* chunksize is 1 */
 int write_jedec_1(struct flashchip *flash, uint8_t * buf)
 {
-	int mask;
-
-	mask = getaddrmask(flash);
-
-	return write_sector_jedec_common(flash, buf, 0, flash->total_size * 1024, mask);
+	return write_sector_jedec_common(flash, buf, 0, flash->total_size * 1024);
 }
 
 /* erase chip with block_erase() prototype */
diff --git a/m29f400bt.c b/m29f400bt.c
index e990d9d..2bca04c 100644
--- a/m29f400bt.c
+++ b/m29f400bt.c
@@ -140,6 +140,7 @@
 	return erase_m29f400bt(flash);
 }
 
+/* chunksize is 1 */
 int write_m29f400bt(struct flashchip *flash, uint8_t *buf)
 {
 	return write_page_m29f400bt(flash, buf, 0, flash->total_size * 1024);
diff --git a/sst28sf040.c b/sst28sf040.c
index ba22093..0c62fd6 100644
--- a/sst28sf040.c
+++ b/sst28sf040.c
@@ -30,7 +30,7 @@
 #define RESET			0xFF
 #define READ_ID			0x90
 
-static void protect_28sf040(struct flashchip *flash)
+int protect_28sf040(struct flashchip *flash)
 {
 	chipaddr bios = flash->virtual_memory;
 
@@ -41,9 +41,11 @@
 	chip_readb(bios + 0x041B);
 	chip_readb(bios + 0x0419);
 	chip_readb(bios + 0x040A);
+
+	return 0;
 }
 
-static void unprotect_28sf040(struct flashchip *flash)
+int unprotect_28sf040(struct flashchip *flash)
 {
 	chipaddr bios = flash->virtual_memory;
 
@@ -54,12 +56,15 @@
 	chip_readb(bios + 0x041B);
 	chip_readb(bios + 0x0419);
 	chip_readb(bios + 0x041A);
+
+	return 0;
 }
 
 int erase_sector_28sf040(struct flashchip *flash, unsigned int address, unsigned int sector_size)
 {
 	chipaddr bios = flash->virtual_memory;
 
+	/* This command sequence is very similar to erase_block_82802ab. */
 	chip_writeb(AUTO_PG_ERASE1, bios);
 	chip_writeb(AUTO_PG_ERASE2, bios + address);
 
@@ -101,10 +106,8 @@
 {
 	chipaddr bios = flash->virtual_memory;
 
-	unprotect_28sf040(flash);
 	chip_writeb(CHIP_ERASE, bios);
 	chip_writeb(CHIP_ERASE, bios);
-	protect_28sf040(flash);
 
 	programmer_delay(10);
 	toggle_ready_jedec(bios);
@@ -116,15 +119,10 @@
 	return 0;
 }
 
+/* chunksize is 1 */
 int write_28sf040(struct flashchip *flash, uint8_t *buf)
 {
-	unprotect_28sf040(flash);
-
-	write_sector_28sf040(flash, buf, 0, flash->total_size * 1024);
-
-	protect_28sf040(flash);
-
-	return 0;
+	return write_sector_28sf040(flash, buf, 0, flash->total_size * 1024);
 }
 
 int erase_chip_28sf040(struct flashchip *flash, unsigned int addr, unsigned int blocklen)
diff --git a/sst49lfxxxc.c b/sst49lfxxxc.c
index c682be3..046b9f3 100644
--- a/sst49lfxxxc.c
+++ b/sst49lfxxxc.c
@@ -75,15 +75,3 @@
 	}
 	return 0;
 }
-
-int write_49lfxxxc(struct flashchip *flash, uint8_t *buf)
-{
-	chipaddr bios = flash->virtual_memory;
-
-	write_lockbits_49lfxxxc(flash, 0);
-	write_page_82802ab(flash, buf, 0, flash->total_size * 1024);
-
-	chip_writeb(0xFF, bios);
-
-	return 0;
-}