Re: [Qemu-devel] PreP kernels boot using Qemu

[Jocelyn Mayer <l_indien@magic.fr>]

On Mon, 2007-10-22 at 09:36 +0200, J. Mayer wrote:
> Hi all,
> 
> I've been investigating more about PreP kernel boot using Qemu and I
> achieved to boot 2.4.35, 2.6.12 and 2.6.22 kernels using Qemu CVS and
> unmodified OHW.
> The issues I found in the kernel are:
> - the OpenFirmware video console driver is broken in recent 2.4 kernels
> and have been removed from recent 2.6 kernel
> - I then decided to use the vga16fb console driver but needed to do some
> patches in order to make it compile properly
> - the CMOS RTC driver is not available for PPC architecture in 2.6
> kernels and need some patches in order to be usable
> - I discovered that the mkprep utility is bugged in 2.4.35 and 2.6.12
> kernels. The bugs are visible only when cross-compiling from a
> little-endian and/or 64 bits host.
> - I got issues (ie process freezing) when using the 2.6.22 kernel with
> HZ > 100. It seems to run properly when the system timer is set to 100
> Hz but this needs more tests for confirmation.
> - I got the 2.6.22 kernel crashing (ie kernel Oops in workqueue code)
> when it has no RTC available. There is no problem when the RTC is
> present. This is likely to be a kernel bug: when no RTC is available, it
> cannot calibrate its timers properly and the kernel timer seems to run
> very fast. Forcing (with hacks...) the timer to run at nearly real-time
> seems to prevent the bug to happen.
> 
> I then generated some kernels that allow me to boot and use those 3
> kernels.
> Here are 3 tarballs with:
> - a patch to be applied to the vanilla kernel sources to fix the
> mentionned bugs
> - the .config file I used to build the kernel
> - the zImage.prep image
> <http://perso.magic.fr/l_indien/qemu-ppc/linux-tests/linux-2.4.35-prep.tar.bz2>
> <http://perso.magic.fr/l_indien/qemu-ppc/linux-tests/linux-2.6.12-prep.tar.bz2>
> <http://perso.magic.fr/l_indien/qemu-ppc/linux-tests/linux-2.6.22-prep.tar.bz2>
> 
> I then run Qemu with the following command line template:
> ./ppc-softmmu/qemu-system-ppc -serial stdio -net nic,model=ne2k_isa -net
> tap -net nic,model=ne2k_pci -net tap -net nic,model=rtl8139 -net tap
> -cpu 604 -M prep -L pc-bios/ -hda <my_first_disk> -cdrom <my_cdrom>
> -kernel
> <src_base>/linux-<kversion>.patched/arch/ppc/boot/images/zImage.prep
> 
> Hope this helps.

Two points I forgot:
- there is no way to make Qemu stop when the PreP kernel displays "Power
down" because the prep_halt routine just does an infinite loop.
- the board reset would not work with the current code. I will fix this
soon.


-- 
Jocelyn Mayer <l_indien@magic.fr>