esp8266/scripts/flashbdev: Correct bootloader flash size to match real size.

Flash size as seen by vendor SDK doesn't depend on real size, but rather on
a particular value in firmware header, as put there by flash tool. That means
it's user responsibility to know what flash size a particular device has, and
specify correct parameters during flashing. That's not end user friendly
however, so we try to make it "flash and play" by detecting real size vs
from-header size mismatch, and correct the header accordingly.

esp8266/scripts/flashbdev.py

@@ -26,6 +26,40 @@ class FlashBdev:
         if op == 5:  # BP_IOCTL_SEC_SIZE
             return self.SEC_SIZE
 
+def set_bl_flash_size(real_size):
+    if real_size == 256*1024:
+        code = 1
+    elif real_size == 512*1024:
+        code = 0
+    elif real_size == 1024*1024:
+        code = 2
+    elif real_size == 2048*1024:
+        code = 3
+    elif real_size == 4096*1024:
+        code = 4
+    else:
+        code = 2
+    buf = bytearray(4096)
+    esp.flash_read(0, buf)
+    buf[3] = (buf[3] & 0xf) | (code << 4)
+    esp.flash_erase(0)
+    esp.flash_write(0, buf)
+
+# If bootloader size ID doesn't correspond to real Flash size,
+# fix bootloader value and reboot.
+size = esp.flash_id() >> 16
+# Check that it looks like realistic power of 2 for flash sizes
+# commonly used with esp8266
+if 22 >= size >= 18:
+    size = 1 << size
+    if size != esp.flash_size():
+        import machine
+        import time
+        print("Bootloader Flash size appear to have been set incorrectly, trying to fix")
+        set_bl_flash_size(size)
+        machine.reset()
+        while 1: time.sleep(1)
+
 if esp.flash_size() < 1024*1024:
     bdev = None
 else: