feat(fs): default drive letter + ESP FS docs (#6367)

Co-authored-by: Gabor Kiss-Vamosi <kisvegabor@gmail.com>

docs/integration/chip/espressif.rst

@@ -78,5 +78,120 @@ These components share a common public API, making it easy to migrate your proje
 To add a display or touch driver to your project, use a command like:
 
 .. code:: sh
-
    idf.py add-dependency "espressif/esp_lcd_gc9a01^2.0.0"
+
+Using the File System under ESP-IDF
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+ESP-IDF uses the standard C functions (``fopen``, ``fread``) in all storage related APIs.
+This allows seamless interoperability with LVGL when enabling the :c:macro:`LV_USE_FS_STDIO` configuration.
+The process is described in details below, using ``SPIFFS`` as demonstration.
+
+- **Decide what storage system you want to use**
+
+   ESP-IDF has many, ready-to-use examples like
+   `SPIFFS <https://github.com/espressif/esp-idf/tree/master/examples/storage/spiffsgen>`__
+   , 
+   `SD Card <https://github.com/espressif/esp-idf/tree/master/examples/storage/sd_card/sdspi>`__ 
+   and 
+   `LittleFS <https://github.com/espressif/esp-idf/tree/master/examples/storage/littlefs>`__
+   .
+
+- **Re-configure your own project**
+
+   The example project should be examined for details, but in general the changes involve:
+
+   - Enabling LVGL's STDIO file system in the configuration
+
+      You can use ``menuconfig``:
+
+         - ``Component config → LVGL configuration → 3rd Party Libraries``: enable ``File system on top of stdio API``
+         - Then select ``Set an upper cased letter on which the drive will accessible`` and set it to ``65`` (ASCII **A**)
+         - You can also set ``Default driver letter`` to 65 to skip the prefix in file paths.
+
+   - Modifying the partition table
+
+      The exact configuration depends on your flash size and existing partitions,
+      but the new final result should look something like this:
+
+      .. code:: csv
+
+         nvs,      data, nvs,     0x9000,  0x6000,
+         phy_init, data, phy,     0xf000,  0x1000,
+         factory,  app,  factory, 0x10000, 1400k,
+         storage,  data, spiffs,         ,  400k,
+
+
+      .. note::
+
+         If you are not using a custom ``parition.csv`` yet, it can be added
+         via ``menuconfig`` (``Partition Table → Partition Table → Custom partition table CSV``).
+
+   - Apply changes to the build system
+
+      Some ESP file systems provide automatic generation from a host folder using CMake. The proper line(s) must be copied to ``main/CMakeLists.txt``
+
+      .. note::
+
+         ``LittleFS`` has extra dependencies that should be added to ``main/idf_component.yml``
+
+- **Prepare the image files**
+
+   LVGL's ``LVGLImage.py`` Python tool can be used to convert images to binary pixel map files.
+   It supports various formats and compression.
+
+   Meanwhile 3rd party libraries
+   (like :ref:`LodePNG<lodepng>` and :ref:`Tiny JPEG<tjpgd>`)
+   allow using image files without conversion.
+
+   After preparing the files, they should be moved to the target device:
+
+   - If properly activated a **SPIFFS** file system based on the ``spiffs_image`` folder should be automatically generated and later flashed to the target
+   - Similar mechanism for **LittleFS** uses the ``flash_data`` folder, but it's only available for Linux hosts
+   - For the **SD Card**, a traditional file browser can be used
+
+- **Invoke proper API calls in the application code**
+
+   The core functionality requires only a few lines. The following example draws the image as well.
+
+   .. code:: c
+
+      #include "esp_spiffs.h"
+
+      void lv_example_image_from_esp_fs(void) {
+
+         esp_vfs_spiffs_conf_t conf = {
+            .base_path = "/spiffs",
+            .partition_label = NULL,
+            .max_files = 5,
+            .format_if_mount_failed = false
+         };
+
+         esp_err_t ret = esp_vfs_spiffs_register(&conf);
+
+         if (ret != ESP_OK) {
+            ESP_LOGE(TAG, "Failed to register SPIFF filesystem");
+            return;
+         }
+
+         lv_obj_t * obj = lv_image_create(lv_screen_active());
+         lv_image_set_src(obj, "A:/spiffs/logo.bin");
+         lv_obj_center(obj);
+      }
+
+- **Build and flash**
+
+   After calling ``idf.py build flash`` the picture should be displayed on the screen.
+
+
+.. note::
+
+   Changes made by ``menuconfig`` are not being tracked in the repository if the ``sdkconfig`` file is added to ``.gitignore``, which is the default for many ESP-IDF projects.
+   To make your configuration permanent, add the following lines to ``sdkconfig.defaults``:
+
+   .. code:: c
+
+      CONFIG_PARTITION_TABLE_CUSTOM=y
+      CONFIG_LV_USE_FS_STDIO=y
+      CONFIG_LV_FS_STDIO_LETTER=65
+      CONFIG_LV_LV_FS_DEFAULT_DRIVE_LETTER=65

docs/integration/chip/renesas.rst

@@ -150,7 +150,7 @@ Get started with the Renesas ecosystem
       The compiler must be activated in e² studio:
 
       - Go to go to ``Help`` -> ``Add Renesas Toolchains``
-      - Press the ``Add... `` button
+      - Press the ``Add...`` button
       - Browse the installation folder of the toolchain
 
       |