[flashrom] [PATCH] Use slow toggle for erase, debug excessive delay

[Carl-Daniel Hailfinger]

Today's systems are quite capable of running 2^32 reads in short time.
Some chips may be slow enough to fall off the loop here. Other chips may
be slow enough to cause delays of more than 2^20 read cycles.

If the JEDEC Toggle Bit algorithm needs more than 2^20 loops, it is a
good sign we should have used delays between toggle bit reads.

The Winbond W39V040C requires a 50 ms delay between toggle bit reads
during erase according to the datasheet. Turns out a 2 ms delay is
sufficient. Use a safety factor of 4 and default all erase operations to
8 ms delay between toggle reads. This is short enough not to have a
substantial negative impact on erase times, and should improve reliability.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006 at gmx.net>

Index: flashrom-detect_excessive_toggle/jedec.c
===================================================================
--- flashrom-detect_excessive_toggle/jedec.c	(Revision 803)
+++ flashrom-detect_excessive_toggle/jedec.c	(Arbeitskopie)
@@ -33,7 +33,7 @@
 	return (val ^ (val >> 1)) & 0x1;
 }
 
-void toggle_ready_jedec(chipaddr dst)
+void toggle_ready_jedec_common(chipaddr dst, int delay)
 {
 	unsigned int i = 0;
 	uint8_t tmp1, tmp2;
@@ -41,14 +41,35 @@
 	tmp1 = chip_readb(dst) & 0x40;
 
 	while (i++ < 0xFFFFFFF) {
+		if (delay)
+			programmer_delay(delay);
 		tmp2 = chip_readb(dst) & 0x40;
 		if (tmp1 == tmp2) {
 			break;
 		}
 		tmp1 = tmp2;
 	}
+	if (i > 0x100000)
+		printf_debug("%s: excessive loops, i=0x%x\n", __func__, i);
 }
 
+void toggle_ready_jedec(chipaddr dst)
+{
+	toggle_ready_jedec_common(dst, 0);
+}
+
+/* Some chips require a minimum delay between toggle bit reads.
+ * The Winbond W39V040C wants 50 ms between reads on sector erase toggle,
+ * but experiments show that 2 ms are already enough. Pick a safety factor
+ * of 4 and use an 8 ms delay.
+ * Given that erase is slow on all chips, it is recommended to use 
+ * toggle_ready_jedec_slow in erase functions.
+ */
+void toggle_ready_jedec_slow(chipaddr dst)
+{
+	toggle_ready_jedec_common(dst, 8 * 1000);
+}
+
 void data_polling_jedec(chipaddr dst, uint8_t data)
 {
 	unsigned int i = 0;
@@ -62,6 +83,8 @@
 			break;
 		}
 	}
+	if (i > 0x100000)
+		printf_debug("%s: excessive loops, i=0x%x\n", __func__, i);
 }
 
 void start_program_jedec(chipaddr bios)
@@ -178,7 +201,7 @@
 	programmer_delay(10);
 
 	/* wait for Toggle bit ready         */
-	toggle_ready_jedec(bios);
+	toggle_ready_jedec_slow(bios);
 
 	if (check_erased_range(flash, page, pagesize)) {
 		fprintf(stderr,"ERASE FAILED!\n");
@@ -207,7 +230,7 @@
 	programmer_delay(10);
 
 	/* wait for Toggle bit ready         */
-	toggle_ready_jedec(bios);
+	toggle_ready_jedec_slow(bios);
 
 	if (check_erased_range(flash, block, blocksize)) {
 		fprintf(stderr,"ERASE FAILED!\n");
@@ -236,7 +259,7 @@
 	chip_writeb(0x10, bios + 0x5555);
 	programmer_delay(10);
 
-	toggle_ready_jedec(bios);
+	toggle_ready_jedec_slow(bios);
 
 	if (check_erased_range(flash, 0, total_size)) {
 		fprintf(stderr,"ERASE FAILED!\n");


-- 
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"We are juggling too many chainsaws and flaming arrows and tigers."