EEPROM support: handle implicit erase

Add support for EEPROMs with 1 byte granularity and implicit erase on
write. flashrom will not try to erase before write on these chips.
Explicitly requested erase with -E is done by writing 0xff.

Corresponding to flashrom svn r1822.
Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>

flash.h

@@ -87,6 +87,7 @@ enum write_granularity {
 	write_gran_528bytes,	/* If less than 528 bytes are written, the unwritten bytes are undefined. */
 	write_gran_1024bytes,	/* If less than 1024 bytes are written, the unwritten bytes are undefined. */
 	write_gran_1056bytes,	/* If less than 1056 bytes are written, the unwritten bytes are undefined. */
+	write_gran_1byte_implicit_erase, /* EEPROMs and other chips with implicit erase and 1-byte writes. */
 };
 
 /*

flashrom.c

@@ -766,6 +766,10 @@ int need_erase(const uint8_t *have, const uint8_t *want, unsigned int len, enum
 	case write_gran_1056bytes:
 		result = need_erase_gran_bytes(have, want, len, 1056);
 		break;
+	case write_gran_1byte_implicit_erase:
+		/* Do not erase, handle content changes from anything->0xff by writing 0xff. */
+		result = 0;
+		break;
 	default:
 		msg_cerr("%s: Unsupported granularity! Please report a bug at "
 			 "flashrom@flashrom.org\n", __func__);
@@ -807,6 +811,7 @@ static unsigned int get_next_write(const uint8_t *have, const uint8_t *want, uns
 	switch (gran) {
 	case write_gran_1bit:
 	case write_gran_1byte:
+	case write_gran_1byte_implicit_erase:
 		stride = 1;
 		break;
 	case write_gran_256bytes: