Re: [Qemu-devel] PowerPC 440 support

[Hollis Blanchard <hollis@penguinppc.org>]

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KVM PPC execution doesn't use firmware today. Instead we create the device
tree in qemu itself, stuff it into guest memory, and point a guest register
at it on entry. This was just a shortcut/hack, because we didn't have enough
time to enable both Linux and uboot.

I agree that the best way to do things long-term is to run u-boot inside the
guest environment. That will likely require improvements to qemu's device
emulation, and also we'll probably need to work out a way for qemu to pass
parameters (e.g. memory size) to u-boot. IMHO, the best approach there would
be to have u-boot interpret a device tree from qemu, then modify it and pass
it on to the kernel. Obviously that will require u-boot work.

-Hollis

On Sun, Jun 14, 2009 at 11:40 PM, Baojun Wang <wangbj@gmail.com> wrote:

> It seems most boards will converted to the device tree infrastructure?
>
> but I think we will need a firmware first before loading the linux
> kernel, I don't know if qemu-system-ppcemb could run kernel directly
> without a firmware..
>
>  Best Regards,
> Wang
>
> On Mon, Jun 15, 2009 at 3:46 AM, Hollis Blanchard<hollis@penguinppc.org>
> wrote:
> > My 440 board is inaccessible for a couple weeks, so I can't test your
> > patch. That said, the code looks fine.
> >
> > However, I wonder what your goal is? You want to be able to create a
> > Bamboo board with e.g. a 750 processor? I don't think that would help
> > the original poster, and I'm not sure how useful it is, but I don't
> > object...
> >
> > Either way I guess it will become a non-issue once PowerPC boards are
> > converted to the device tree infrastructure.
> >
> > -Hollis
> >
> > On Sun, Jun 14, 2009 at 1:33 PM, Blue Swirl<blauwirbel@gmail.com> wrote:
> >> Sorry, I was very confused (I didn't look at ppc440.c).
> >>
> >> For some reason, CPU model can't be specified on the command line. The
> >> patch allows this, does it look OK?
> >>
> >> Is there a kernel and initrd somewhere, so I could test this?
> >>
> >> Currently I get (no kernel or ROM, so nothing to execute):
> >> Truncating memory to 128 MiB to fit SDRAM controller limits.
> >> ppc405_serial_init: offset 0000000000000300
> >> QEMU 0.10.50 monitor - type 'help' for more information
> >> (qemu) qemu: fatal: Trying to execute code outside RAM or ROM at
> >> 0x00000000fffffffc
> >>
> >> NIP 00000000fffffffc   LR 0000000000000000 CTR 0000000000000000 XER
> 00000000
> >> MSR 0000000000000000 HID0 0000000000000300  HF 0000000000000000 idx 1
> >> Segmentation fault
> >>
> >> On 6/14/09, Hollis Blanchard <hollis@penguinppc.org> wrote:
> >>> Yes, I wrote the code you quoted.
> >>>
> >>>  In case there is any confusion, let me restate: You can boot a Bamboo
> >>>  (PowerPC 440) guest under KVM on a PowerPC 440 host. KVM bypasses
> >>>  qemu's CPU emulation (TCG), but uses qemu's device emulation.
> >>>  Therefore, if someone were to implement 440 core emulation in qemu,
> >>>  you could boot a 440 kernel with qemu without KVM.
> >>>
> >>>  Most devices found on 440 SoCs are the same as or very similar to the
> >>>  devices found on 405 SoCs. Qemu's 440 device emulation isn't perfect,
> >>>  but because Linux is highly modular, with a modified device tree you
> >>>  can boot it. See pc-bios/bamboo.dts.
> >>>
> >>>  -Hollis
> >>>
> >>>  On Sat, Jun 13, 2009 at 10:47 PM, Baojun Wang <wangbj@gmail.com>
> wrote:
> >>>  >
> >>>  > in hw/ppc440.c:
> >>>  >
> >>>  >    env = cpu_ppc_init("440EP");
> >>>  >    if (!env && kvm_enabled()) {
> >>>  >        /* XXX Since qemu doesn't yet emulate 440, we just say it's a
> 405.
> >>>  >         * Since KVM doesn't use qemu's CPU emulation it seems to be
> working
> >>>  >         * OK. */
> >>>  >        env = cpu_ppc_init("405");
> >>>  >    }
> >>>  >    if (!env) {
> >>>  >        fprintf(stderr, "Unable to initialize CPU!\n");
> >>>  >        exit(1);
> >>>  >    }
> >>>  >
> >>>  > also in hw/ppc.c:
> >>>  >
> >>>  > I can find ppc40x_irq_init/e500_irq_init(used mpc8544ds), but there
> is
> >>>  > no ppcbooke_irq_init? It seems hw/ppc405_uc.c is emulation for DCRs,
> >>>  > PLB, DMA, GPIO, I2C.., but there is no hw/ppc44x_uc.c.
> >>>  >
> >>>  > the qemu source I used is 0.10.5.
> >>>  >
> >>>  > Also in ppc/translate_init.c, there lots of CONFIG_USER_ONLY, but I
> >>>  > many of them are DEBUG or CACHE related SPR emulation, and since
> qemu
> >>>  > doesn't emulate cache, I think it's OK.
> >>>  >
> >>>  >  Thanks,
> >>>  > Wang
> >>>  >
> >>>  > On Sun, Jun 14, 2009 at 1:47 AM, Hollis Blanchard<
> hollis@penguinppc.org> wrote:
> >>>  > > On Fri, Jun 12, 2009 at 10:48 AM, Blue Swirl <
> blauwirbel@gmail.com> wrote:
> >>>  > >>
> >>>  > >> On 6/11/09, Baojun Wang <wangbj@gmail.com> wrote:
> >>>  > >> > could qemu emulate some board like bamboo (without kvm) or
> MPC8544ds
> >>>  > >> > now? Thanks
> >>>  > >>
> >>>  > >> Yes, if someone adds emulation for these devices: UIC, PLB, DMA,
> POB,
> >>>  > >> EBC, IIC, ZMII. Maybe some are not needed in all cases.
> >>>  > >
> >>>  > > No, qemu still doesn't emulate Book E cores, such as the PowerPC
> 440 in a
> >>>  > > Bamboo board.
> >>>  > >
> >>>  > > UIC is of course emulated, otherwise KVM guests on 440 wouldn't
> get very
> >>>  > > far. :) Enough 440 SoC devices are emulated to support Linux boot
> with a
> >>>  > > properly stripped device tree.
> >>>  > >
> >>>  > > -Hollis
> >>>  > >
> >>>
> >>
> >
>

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