Always read the flash chip before writing

This will allow flashrom to skip erase of already-erased blocks and to
skip write of blocks which already have the wanted contents.

Avoid emergency messages by checking if the chip contents after a failed
write operation (erase/write) are unchanged.

Keep the emergency messages after a failed pure erase. That part is
debatable because if someone wants erase, he pretty sure doesn't care
about the flash contents anymore.

Please note that this introduces additional overhead of a full chip read
before write. This is frowned upon by people with slow programmers. A
followup patch will make this configurable.

Corresponding to flashrom svn r1215.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Stefan Reinauer <stepan@coreboot.org>

flash.h

@@ -239,7 +239,7 @@ int cli_classic(int argc, char *argv[]);
 /* layout.c */
 int read_romlayout(char *name);
 int find_romentry(char *name);
-int handle_romentries(uint8_t *buffer, struct flashchip *flash);
+int handle_romentries(struct flashchip *flash, uint8_t *oldcontents, uint8_t *newcontents);
 
 /* spi.c */
 struct spi_command {