[BUG] Default configuration values hardcoded in code

[raiden00pl]

Description / Steps to reproduce the issue

There are many places in NuttX where configuration defaults are set in the source code, not from Kconfig.

This should be handled by Kconfig only otherwise it can lead to hard to detect problems like in this issue #16256

We can find these definitions using simple commands:

• git grep "#define CONFIG"
• git grep " # define CONFIG"
• git grep " #define CONFIG"

Some results returned in this way are false positives, so additional verification is required.

In some way the problem is related to this issue #11637

Another related problem is the use of #define CONFIG_ for definitions that don't come from Kconfig. Shouldn't definitions in this format be reserved for Kconfig only? When I see CONFIG_XXX_YYY definition used somewhere in the code I expect it to be defined in .config / include/nuttx/config.h, which is often not true in NuttX.

On which OS does this issue occur?

[OS: Linux]

What is the version of your OS?

NuttX Version

Issue Architecture

[Arch: all]

Issue Area

[Area: Configuring]

Host information

No response

Verification

• I have verified before submitting the report.

[acassis]

@raiden00pl I think most of those "failsafe" #ifndef / #define comes from an era when NuttX didn't use Kconfig. Since Kconfig introduction it doesn't make sense anymore.

[xiaoxiang781216]

if these macros can't migrate to Kconfig soon, it's better to remove CONFIG_ prefix and #ifndef check to avoiding confuse people.

[acassis]

@xiaoxiang781216 I think one downside of removing CONFIG_ is that these macros may become hard to find later. It's better to remove them step by step, adding them to Kconfig.

[siddhitripathi25]

Hi @raiden00pl , @acassis, @xiaoxiang781216,

I'm a first-year student contributing to the nuttx-website repository, and I'm
interested in helping address the documentation aspects of this issue.

I've observed that:

1. This issue demonstrates a fundamental confusion point: users see CONFIG_
   macros in code and assume they come from Kconfig/.config
2. The discussion shows this is a widespread problem ("many places in NuttX")
3. The community is actively discussing solutions

As part of improving NuttX documentation, I'm proposing to create a
comprehensive Configuration Guide that would help users understand:

• Where configuration values should come from (Kconfig only)
• Why hardcoded CONFIG_ defines in source code are problematic
• How to identify and work around existing hardcoded values
• Best practices for configuration (addressing the "remove CONFIG_ prefix"
  suggestion from @xiaoxiang781216)

I'd like to ensure my documentation addresses the pain points raised here.
Specifically, would it be helpful to include:

1. A section explaining "CONFIG_ macros: Kconfig vs Source Code"
2. Guidance on how to verify if a CONFIG_ value truly comes from Kconfig
3. Migration tips for when these hardcoded values are eventually moved to Kconfig

This documentation would complement the code cleanup work discussed here.

Thank you for raising this important issue!

Best regards,
Siddhi Tripathi