Unable to find rootfs after kernel_menuconfig

[Rogier Lodewijks]

In the pursuit to track down my SPI issues I've reconfigured my kernel to not include the mt7621 SPI HW driver.

The patch to the .config is almost trivially simple:

diff --git a/target/linux/ramips/mt7688/config-4.4 b/target/linux/ramips/mt7688/config-4.4
index c4a844da38..6fc9a91e6d 100644
--- a/target/linux/ramips/mt7688/config-4.4
+++ b/target/linux/ramips/mt7688/config-4.4
@@ -225,8 +225,11 @@ CONFIG_SOC_MT7620=y
 # CONFIG_SOC_RT3883 is not set
 CONFIG_SOUND=m
 CONFIG_SPI=y
+CONFIG_SPI_BITBANG=y
+CONFIG_SPI_DEBUG=y
+CONFIG_SPI_GPIO=y
 CONFIG_SPI_MASTER=y
-CONFIG_SPI_MT7621=y
+# CONFIG_SPI_MT7621 is not set
 # CONFIG_SPI_RT2880 is not set
 CONFIG_SRCU=y
 CONFIG_SWCONFIG=y

Building a new image works fine, but the resulting image -somehow- is not booting. I did not touch anything other that the patch above. Here is the kernel boot output deemed important:

[    0.000000] Kernel command line: console=ttyS0,115200 rootfstype=squashfs,jffs2

**snip**

[    0.435122] VFS: Cannot open root device "(null)" or unknown-block(0,0): error -6
[    0.442720] Please append a correct "root=" boot option; here are the available partitions:
[    0.451254] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[    0.460532] Rebooting in 1 seconds..

Seemingly the kernel is not correctly pointed towards the rootfs. Isn't it u-boot's job to inform the kernel of the whereabouts of the rootfs and the layout of the MTD main storage device?

Me not (yet :)) being an OpwnWRT/Buildroot expert, it's probably something trivial I'm overlooking here. Any handles anyone?