[U-Boot] [PATCH 3/4] x86: doc: Mention qemu-x86_64 support

[Bin Meng]

Hi Heinrich,

On Thu, Oct 11, 2018 at 11:32 PM Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>
> On 10/11/2018 05:27 PM, Bin Meng wrote:
> > Hi Heinrich,
> >
> > On Thu, Oct 11, 2018 at 11:15 PM Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
> >>
> >> On 10/11/2018 03:53 AM, Bin Meng wrote:
> >>> Currently only 32-bit U-Boot for QEMU x86 is documented. Mention
> >>> the 64-bit support.
> >>>
> >>> Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
> >>> ---
> >>>
> >>>  doc/README.x86 | 8 ++++++--
> >>>  1 file changed, 6 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/doc/README.x86 b/doc/README.x86
> >>> index 8cc4672..ab48466 100644
> >>> --- a/doc/README.x86
> >>> +++ b/doc/README.x86
> >>> @@ -32,7 +32,7 @@ are supported:
> >>>     - Link (Chromebook Pixel)
> >>>     - Minnowboard MAX
> >>>     - Samus (Chromebook Pixel 2015)
> >>> -   - QEMU x86
> >>> +   - QEMU x86 (32-bit & 64-bit)
> >>>
> >>>  As for loading an OS, U-Boot supports directly booting a 32-bit or 64-bit
> >>>  Linux kernel as part of a FIT image. It also supports a compressed zImage.
> >>> @@ -376,7 +376,9 @@ QEMU x86 target instructions for bare mode:
> >>>
> >>>  To build u-boot.rom for QEMU x86 targets, just simply run
> >>>
> >>> -$ make qemu-x86_defconfig
> >>> +$ make qemu-x86_defconfig (for 32-bit)
> >>> +or
> >>> +$ make qemu-x86_64_defconfig (for 64-bit)
> >>>  $ make all
> >>
> >> If your patch series creates a U-Boot usable with QEMU depends on the
> >> chosen CPU:
> >>
> >> This one seems to work:
> >> qemu-system-x86_64 -bios u-boot.rom -nographic -cpu core2duo
> >>
> >> This one fails (as expected):
> >> qemu-system-x86_64 -bios u-boot.rom --nographic -cpu pentium
> >
> > Pentium does not support 64-bit, so it is expected. In my testing I
> > always omit the '-cpu' so this is not a problem. But I can document
> > this.
> >
> >>
> >> I could not get the emulation running without -nographic. Do you know why?
> >>
> >
> > This is due to currently the VGA support is missing in the 64-bit U-Boot.
> >
> >> The documentation above is insufficient. Please, provide a minimum QEMU
> >> command line which includes a CPU specification.
> >>
> >> I would prefer if you could specify two lines per bitness - one with kvm
> >> and one without, e.g.
> >
> > I doubt -enable-kvm works with U-Boot.
>
> Why? It is just an instruction how QEMU should emulate the CPU. KVM does
> not require anything on the target software side.
>
> I have had no problem with KVM on the i386 target.

I suspect some drivers may have issues when working with KVM, eg: some
memory barriers might be needed due to guest (U-Boot) and host (x86
machine) are speaking the same language. But I have never fully test
this configuration.

Regards,
Bin