How can I deactivate a kernel option?

Question

I want to deactivate a kernel option during my build:

In a .bbappend file for the kernel recipe I fetch via SRC_URI a .cfg kernel fragment file no_usb.cfg with this content:

CONFIG_USB=n
CONFIG_USB_TEST=y

The first entry is supposed to turn USB off in the kernel configuration, the second entry is for testing the reverse case.

This didn't work: Neither the test entry appeared nor the USB was deactivated. I have also seen in the yocto sources *.scc files and I created one for my no_usb.cfg:

kconf hardware no_usb.cfg

But I found only less in the documentation and couldn't turn USB off. So how can I deactivate CONFIG_USB?

This is my kernel recipe (from freescale SDK) linux-qoriq_3.12.bb:

require recipes-kernel/linux/linux-qoriq.inc
SRC_URI = "git://git.freescale.com/ppc/sdk/linux.git;branch=sdk-v1.9.x"
SRCREV = "43cecda943a6c40a833b588801b0929e8bd48813"

I have a layer with this append file linux-qoriq_3.12.bbappend:

SRC_URI += "file://no_usb.cfg"

The directory structure of the layer is following:

meta-layer
└── recipes-kernel
    └── linux
        ├── linux-qoriq
        │   └── no_usb.cfg
        └── linux-qoriq_3.12.bbappend

Answer 1

As was stated by the previous commenter, you need to use # CONFIG_FOO is not set rather than CONFIG_FOO=n. I would like to make one correction, though. The linux-qoriq recipe does support configuration fragments, it just uses a separate variable to control their usage, DELTA_KERNEL_DEFCONFIG. See the do_configure_prepend in recipes-kernel/linux/linux-qoriq.inc for details.

In your append, you should be able to add this to fix it:

DELTA_KERNEL_DEFCONFIG += "no_usb.cfg"