Add upgrade notes

docs/source/upgrading/5.1-5.2.rst

@@ -91,3 +91,23 @@ These will now fail to compile.
 Copy construction and assignment has been explicitly deleted so avoid unintentional side-effects.
 
 Objects should always be passed by reference.
+
+
+**spi_flash functions**
+
+Several definitions have been deprecated/removed as they serve no purpose since partitions introduced.
+
+``flashmem_get_first_free_block_address()``
+
+``flashmem_get_info()`` returns a common ``SPIFlashInfo`` structure for all architectures.
+Esp8266 previously had a structure definition with two ``unknown`` fields as this directly represented
+the contents of the first 16 bytes of flash. These have been removed and the structure unpacked.
+
+The following macro definitions have been removed for esp8266:
+
+- ``SYS_PARAM_SEC_COUNT``
+- ``FLASH_WORK_SEC_COUNT``
+- ``INTERNAL_FLASH_SIZE``
+
+These related to the fixed system paramter block at the end of flash memory.
+With partitions this is relocatable so any code which depends on these will be wrong.