Rebuilding kernel doesn't rebuild sdcard image

[Craig McQueen <craig.mcqueen@beamcommunications.com>]

I'm trying out Yocto to build core-image-minimal for imx28evk. I was 
able to build with the linux-imx kernel provider (which builds a 2.6.35 
kernel), and then switch to linux-fslc kernel provider (3.14.19 kernel). 
That seemed fine.

But now I am trying to switch back to linux-imx kernel provider, to 
check some things with the 2.6.35 kernel. But when I write the sdcard 
image then boot, I find the sdcard image still contains the 3.14.19 kernel.

I tried:

     bitbake -c cleansstate linux-fslc
     bitbake -c cleansstate linux-imx
     bitbake core-image-minimal

But still the sdcard image contains the 3.14.19 kernel.

I had a closer look at what's in the build/tmp/deploy/images/imx28evk 
directory. Here is the latest .sdcard file, and the latest uImage file:

     -rw-r--r-- 1 craigm craigm 83886080 Nov 10 16:25 
core-image-minimal-imx28evk-20141110052334.rootfs.sdcard
     -rw-r--r-- 2 craigm craigm  2612944 Nov 10 17:13 
uImage--2.6.35.3-r45-imx28evk-20141110060936.bin

I check the uImage file:

     file uImage--2.6.35.3-r45-imx28evk-20141110060936.bin
     uImage--2.6.35.3-r45-imx28evk-20141110060936.bin: u-boot legacy 
uImage, Linux-2.6.35.3-maintain+yocto+gb, Linux/ARM, OS Kernel Image 
(Not compressed), 2612880 bytes, Mon Nov 10 17:12:44 2014, Load Address: 
0x40008000, Entry Point: 0x40008000, Header CRC: 0x35886962, Data CRC: 
0x37FEB8CE

So the uImage has been built fine. But it looks as though the 
core-image-minimal-imx28evk-xxxx.rootfs.sdcard has not been subsequently 
rebuilt. Perhaps the .sdcard file is only rebuilt if the root file 
system changes, but not if the kernel only changes.

To confirm this, I mount the SD card and check its contents, and I see 
the uImage still contains a 3.14.19 kernel:

     file /media/craigm/Boot\ imx28e/uImage
     /media/craigm/Boot imx28e/uImage: u-boot legacy uImage, 
Linux-3.14.19-fslc+g00e4721, Linux/ARM, OS Kernel Image (Not 
compressed), 3586912 bytes, Mon Nov 10 12:10:21 2014, Load Address: 
0x40008000, Entry Point: 0x40008000, Header CRC: 0x9CFC9D94, Data CRC: 
0x7C476150


After this, I tried to force an SD card image rebuild, by rebuilding an 
arbitrary package:

     bitbake -c cleansstate nano
     bitbake core-image-minimal

It rebuilt nano, but didn't rebuild _any_ of the images in 
build/tmp/deploy/images/imx28evk. So it looks as though the problem is 
bigger than I originally thought. I'm fairly new to Yocto, so I'm not 
sure what is going on here.


Is it possible to update the recipe that builds the .sdcard file and 
other images, to ensure it will run after any kernel or root filesystem 
change? Meanwhile as a work-around, what is the command to manually 
re-run this step?

Thanks,
Craig McQueen