+/**
+ * Write a block of data to SPI flash, first checking if it is different from
+ * what is already there.
+ *
+ * If the data being written is the same, then *skipped is incremented by len.
+ *
+ * @param flash flash context pointer
+ * @param offset flash offset to write
+ * @param len number of bytes to write
+ * @param buf buffer to write from
+ * @param cmp_buf read buffer to use to compare data
+ * @param skipped Count of skipped data (incremented by this function)
+ * @return NULL if OK, else a string containing the stage which failed
+ */
+static const char *spi_flash_update_block(struct spi_flash *flash, u32 offset,
+ size_t len, const char *buf, char *cmp_buf, size_t *skipped)
+{
+ debug("offset=%#x, sector_size=%#x, len=%#zx\n",
+ offset, flash->sector_size, len);
+ if (spi_flash_read(flash, offset, len, cmp_buf))
+ return "read";
+ if (memcmp(cmp_buf, buf, len) == 0) {
+ debug("Skip region %x size %zx: no change\n",
+ offset, len);
+ *skipped += len;
+ return NULL;
+ }
+ if (spi_flash_erase(flash, offset, len))
+ return "erase";
+ if (spi_flash_write(flash, offset, len, buf))
+ return "write";
+ return NULL;
+}
+
+/**
+ * Update an area of SPI flash by erasing and writing any blocks which need
+ * to change. Existing blocks with the correct data are left unchanged.
+ *
+ * @param flash flash context pointer
+ * @param offset flash offset to write
+ * @param len number of bytes to write
+ * @param buf buffer to write from
+ * @return 0 if ok, 1 on error
+ */
+static int spi_flash_update(struct spi_flash *flash, u32 offset,
+ size_t len, const char *buf)
+{
+ const char *err_oper = NULL;
+ char *cmp_buf;
+ const char *end = buf + len;
+ size_t todo; /* number of bytes to do in this pass */
+ size_t skipped = 0; /* statistics */
+
+ cmp_buf = malloc(flash->sector_size);
+ if (cmp_buf) {
+ for (; buf < end && !err_oper; buf += todo, offset += todo) {
+ todo = min(end - buf, flash->sector_size);
+ err_oper = spi_flash_update_block(flash, offset, todo,
+ buf, cmp_buf, &skipped);
+ }
+ } else {
+ err_oper = "malloc";
+ }
+ free(cmp_buf);
+ if (err_oper) {
+ printf("SPI flash failed in %s step\n", err_oper);
+ return 1;
+ }
+ printf("%zu bytes written, %zu bytes skipped\n", len - skipped,
+ skipped);
+
+ return 0;