[flashrom] [PATCH] Check if an erase is needed to write

[Carl-Daniel Hailfinger]

For optimal partial reflashing, we have to find out which parts of the
chip can be written without erase. For that, the only criterion (except
a limit on the number of writes for very old chips) is whether the write
will only clear bits (set them to 0).
If (current&new==new) we can skip the erase.
If any bit would have to be set to 1, we need to erase.

Signed-off-by: Carl-Daniel Hailfinger

Index: flashrom-need_erase/flash.h
===================================================================
--- flashrom-need_erase/flash.h	(Revision 725)
+++ flashrom-need_erase/flash.h	(Arbeitskopie)
@@ -455,6 +455,7 @@
 int max(int a, int b);
 int check_erased_range(struct flashchip *flash, int start, int len);
 int verify_range(struct flashchip *flash, uint8_t *cmpbuf, int start, int len, char *message);
+int need_erase(uint8_t *have, uint8_t *want, int len);
 char *strcat_realloc(char *dest, const char *src);

#define OK 0
Index: flashrom-need_erase/flashrom.c
===================================================================
--- flashrom-need_erase/flashrom.c	(Revision 725)
+++ flashrom-need_erase/flashrom.c	(Arbeitskopie)
@@ -379,6 +379,26 @@
    return ret;
 }

+/**
+ * Check if the buffer have can be programmed to the content of want without
+ * erasing. This is only possible if no bit has to be set to 1.
+ *
+ * @have        buffer with current content
+ * @want        buffer with desired content
+ * @len         length of the verified area
+ * @return      0 if no erase is needed, >0 otherwise
+ */
+int need_erase(uint8_t *have, uint8_t *want, int len)
+{
+	int failcount = 0;
+	int i;
+
+	for (i = 0; i < len; i++)
+		if ((have[i] & want[i]) != want[i])
+			failcount++;
+	return failcount;
+}
+
 struct flashchip *probe_flash(struct flashchip *first_flash, int force)
 {
    struct flashchip *flash;