manual: board support: add more of our expectations

The manual has a section on adding board support to upstream buildroot,
but it fails to mention some of the things we expect. Add more of them.

- Internal toolchain.
- Beautify defconfig file.
- Fixed versions for components.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <[email protected]>
Cc: Adam Duskett <[email protected]>
Reviewed-by: Adam Duskett <[email protected]>
[[email protected]:
  - use +monospace+ for the variables
  - use _italic_ for sections in defconfig
]
Signed-off-by: Yann E. MORIN <[email protected]>

docs/manual/adding-board-support.txt

@@ -10,9 +10,9 @@ that is known to work. You are welcome to add support for other boards
 to Buildroot too.
 
 To do so, you need to create a normal Buildroot configuration that
-builds a basic system for the hardware: toolchain, kernel, bootloader,
-filesystem and a simple BusyBox-only userspace. No specific package
-should be selected: the configuration should be as minimal as
+builds a basic system for the hardware: (internal) toolchain, kernel,
+bootloader, filesystem and a simple BusyBox-only userspace. No specific
+package should be selected: the configuration should be as minimal as
 possible, and should only build a working basic BusyBox system for the
 target platform. You can of course use more complicated configurations
 for your internal projects, but the Buildroot project will only
@@ -22,7 +22,17 @@ selections are highly application-specific.
 Once you have a known working configuration, run +make
 savedefconfig+. This will generate a minimal +defconfig+ file at the
 root of the Buildroot source tree. Move this file into the +configs/+
-directory, and rename it +<boardname>_defconfig+.
+directory, and rename it +<boardname>_defconfig+. If the configuration
+is a bit more complicated, it is nice to manually reformat it and
+separate it into sections, with a comment before each section. Typical
+sections are _Architecture_, _Toolchain options_ (typically just linux
+headers version), _Firmware_, _Bootloader_, _Kernel_, and _Filesystem_.
+
+Always use fixed versions or commit hashes for the different
+components, not the "latest" version. For example, set
++BR2_LINUX_KERNEL_CUSTOM_VERSION=y+ and
++BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE+ to the kernel version you tested
+with.
 
 It is recommended to use as much as possible upstream versions of the
 Linux kernel and bootloaders, and to use as much as possible default