Custom kernel: fails to load firmware when module built-in

Question

I'd like to have all my modules built-in, but this fails with iwlagn:

iwlagn 0000:03:00.0: request for firmware file 'iwlwifi-6000-4.ucode' failed.
iwlagn 0000:03:00.0: no suitable firmware found!

The microcode file exists in /lib/firmware and the whole thing works just fine if I compile iwlagn as module. I have no idea where it's looking for the file or what's wrong - any ideas?

Solution

Have a look at the CONFIG_FIRMWARE_IN_KERNEL, CONFIG_EXTRA_FIRMWARE, and CONFIG_EXTRA_FIRMWARE_DIR configuration options (found at Device Drivers -> Generic Driver Options).

The first option will enable firmware being built into the kernel, the second one should contain the firmware filename (or a space-separated list of names), and the third where to look for the firmware.

So in your example, you would set those options to:

CONFIG_FIRMWARE_IN_KERNEL=y
CONFIG_EXTRA_FIRMWARE='iwlwifi-6000-4.ucode'
CONFIG_EXTRA_FIRMWARE_DIR='/lib/firmware'

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A word of advise: Compiling all modules into the kernel is not a good idea. I think I understand your ambition because at some point I was also desperate to do it. The problem with such approach is that you cannot unload the module once it is built-in - and, unfortunately especially the wireless drivers tend to be buggy which leads to a necessity of re-loading their modules. Also, in some cases, a module version of a recent driver will just not work.

Comments

[orpheuswasrebornhere]

Making a new answer instead a comment; EXTRA_FIRMWARE_DIR corresponds to the firmware blob locations in the build environment; not the target. see (cateee.net/lkddb/web-lkddb/EXTRA_FIRMWARE_DIR.html)

[LtWorf]

That is no longer true. Intel drivers are stable and work fine for days without any manual intervention needed.

[arved]

EXTRA_FIRMWARE only works on 64bit kernels according to the documentation