[yocto] custom linux kernel recipe

[Mircea Gliga]

Hi

I'm using krogoth and trying to create a qemu arm machine with the 
latest stable kernel 4.7.2.
I created a recipe,recipes-kernel/linux/linux-stable_4.7.bb, in my layer 
with the following contents:

---
inherit kernel
require recipes-kernel/linux/linux-yocto.inc

FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}-${PV}:"

KBRANCH ?= "linux-4.7.y"

SRCREV ?= "84fae3f89282ce86a0c0da30e35fe66dbcadda6f"

KBRANCH_sama5d4-xplained ?= "linux-4.7.y"
SRCREV_machine_sama5d4-xplained ?= 
"84fae3f89282ce86a0c0da30e35fe66dbcadda6f"

KERNEL_DEVICETREE_sama5d4-xplained = "at91-sama5d4_xplained.dtb"

KBRANCH_qemuarm ?= "linux-4.7.y"

SRC_URI = 
"git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git;bareclone=1;branch=${KBRANCH}"

SRC_URI += "file://defconfig"

LINUX_VERSION = "4.7.2"
PV = "${LINUX_VERSION}+git${SRCPV}"

COMPATIBLE_MACHINE = "sama5d4-xplained|qemuarm"
---

As you can see, I'm planning to use this recipe for multiple machines.

In the recipes-kernel/linux/linux-stable-4.7/qemuarm/ directory I copied 
the defconfig file.
I've created this defconfig file by:
* sourcing my build environment, from my build directory: source 
build-qemu/tmp/environment-setup-armv5e-poky-linux-gnueabi
* running "make vexpress_defconfig" in the kernel build directory. (I've 
used this tutorial 
https://balau82.wordpress.com/2012/03/31/compile-linux-kernel-3-2-for-arm-and-emulate-with-qemu/ 
)
This outputed:

---
$ make vexpress_defconfig
   GEN     ./Makefile
#
# configuration written to .config
#
---

* renamed .config to defconfig and then copy it in 
recipes-kernel/linux/linux-stable-4.7/qemuarm/

In my local.conf I've added, in order to use my custom kernel for the 
qemu machine:

---
MACHINE ??= "qemuarm"
PREFERRED_PROVIDER_virtual/kernel_qemuarm ?= "linux-stable"
---

Everything builds without errors (bitbake linux-stable), but when I 
start qemu (runqemu qemuarm) I only get a black screen in the QEMU window.
This is the output of $ runqemu qemuarm:
---
Continuing with the following parameters:
KERNEL: 
[/home/user/yocto-k/build-qemu/tmp/deploy/images/qemuarm/zImage-qemuarm.bin]
ROOTFS: 
[/home/user/yocto-k/build-qemu/tmp/deploy/images/qemuarm/custom-minimal-image-qemuarm-20160823102657.rootfs.ext4]
FSTYPE: [ext4]
Setting up tap interface under sudo
[sudo] password for user:
Acquiring lockfile for tap0...
Running qemu-system-arm...
/home/user/yocto-k/build-qemu/tmp/sysroots/x86_64-linux/usr/bin/qemu-system-arm 
-kernel 
/home/user/yocto-k/build-qemu/tmp/deploy/images/qemuarm/zImage-qemuarm.bin 
-net nic,model=virtio -net 
tap,vlan=0,ifname=tap0,script=no,downscript=no -M versatilepb -drive 
file=/home/user/yocto-k/build-qemu/tmp/deploy/images/qemuarm/custom-minimal-image-qemuarm-20160823102657.rootfs.ext4,if=virtio,format=raw 
-no-reboot -show-cursor -usb -usbdevice tablet -no-reboot -m 128 -serial 
mon:vc -serial null -append "root=/dev/vda rw console=ttyAMA0,115200 
console=tty ip=192.168.7.2::192.168.7.1:255.255.255.0 mem=128M 
highres=off rootfstype=ext4 "
---

This is my build configuration:
Build Configuration:
BB_VERSION        = "1.30.0"
BUILD_SYS         = "x86_64-linux"
NATIVELSBSTRING   = "universal"
TARGET_SYS        = "arm-poky-linux-gnueabi"
MACHINE           = "qemuarm"
DISTRO            = "poky"
DISTRO_VERSION    = "2.1.1"
TUNE_FEATURES     = "arm armv5 thumb dsp"
TARGET_FPU        = "soft"
meta
meta-poky
meta-yocto-bsp    = "krogoth:12eb72ee3b02f826a156ff4e396c770f2b93571e"
meta-smartcom     = "master:121dbfb9f416de8442bbad1dc150271fd50b38e6"
meta-atmel        = "krogoth:01ff01073dd8fa1463b7841fb0a8caa44559acdd"
meta-oe
meta-networking
meta-python       = "krogoth:247b1267bbe95719cd4877d2d3cfbaf2a2f4865a"


When I use the default linux-yocto as the preferred kernel (v 4.4) 
everything works as expected.
Do you have any suggestions? Is there a problem with the defconfig file 
provided ?
What is the proper way of creating this defconfig file for qemuarm ?
I also tried using the .config file created when building 
linux-yocto_4.4 but got the same result.
I tried the defconfig used for the

Thanks !