feat(nvs): Allow read-only NVS partitions smaller than 0x3000

E.g. for factory settings data

Closes https://github.com/espressif/esp-idf/issues/15317

components/nvs_flash/host_test/nvs_page_test/main/test_fixtures.hpp

@@ -110,7 +110,7 @@ public:
         size_t columns = size / column_size;
         size_t column;
 
-        for(column = 0; column < columns; column = column + 1)
+        for(column = 0; column < columns; ++column)
         {
             // read column
             if((err = esp_partition_read_raw(&esp_partition, dst_offset + (column * column_size), buff, column_size)) != ESP_OK) return err;

components/nvs_flash/src/nvs_pagemanager.cpp

@@ -124,8 +124,8 @@ esp_err_t PageManager::load(Partition *partition, uint32_t baseSector, uint32_t
         }
     }
 
-    // partition should have at least one free page
-    if (mFreePageList.empty()) {
+    // partition should have at least one free page if it is not read-only
+    if (!partition->get_readonly() && mFreePageList.empty()) {
         return ESP_ERR_NVS_NO_FREE_PAGES;
     }
 

components/partition_table/gen_esp32part.py

@@ -7,7 +7,7 @@
 # See https://docs.espressif.com/projects/esp-idf/en/latest/api-guides/partition-tables.html
 # for explanation of partition table structure and uses.
 #
-# SPDX-FileCopyrightText: 2016-2024 Espressif Systems (Shanghai) CO LTD
+# SPDX-FileCopyrightText: 2016-2025 Espressif Systems (Shanghai) CO LTD
 # SPDX-License-Identifier: Apache-2.0
 import argparse
 import binascii
@@ -31,7 +31,7 @@ SECURE_NONE = None
 SECURE_V1 = 'v1'
 SECURE_V2 = 'v2'
 
-__version__ = '1.4'
+__version__ = '1.5'
 
 APP_TYPE = 0x00
 DATA_TYPE = 0x01
@@ -45,6 +45,8 @@ TYPES = {
     'data': DATA_TYPE,
 }
 
+NVS_RW_MIN_PARTITION_SIZE = 0x3000
+
 
 def get_ptype_as_int(ptype):
     """ Convert a string which might be numeric or the name of a partition type to an integer """
@@ -533,6 +535,11 @@ class PartitionDefinition(object):
             raise ValidationError(self, "'%s' partition of type %s and subtype %s is always read-write and cannot be read-only" %
                                   (self.name, self.type, self.subtype))
 
+        if self.type == TYPES['data'] and self.subtype == SUBTYPES[DATA_TYPE]['nvs']:
+            if self.size < NVS_RW_MIN_PARTITION_SIZE and self.readonly is False:
+                raise ValidationError(self, """'%s' partition of type %s and subtype %s of this size (0x%x) must be flagged as 'readonly' \
+(the size of read/write NVS has to be at least 0x%x)""" % (self.name, self.type, self.subtype, self.size, NVS_RW_MIN_PARTITION_SIZE))
+
     STRUCT_FORMAT = b'<2sBBLL16sL'
 
     @classmethod