Re: Why VESA and DPMS are available only for i386?

On Monday 15 September 2008 09:05 pm, Carlos A. M. dos Santos wrote:
> On Mon, Sep 15, 2008 at 3:39 PM, Jung-uk Kim <jkim_at_freebsd.org> 
wrote:
> > On Monday 15 September 2008 01:24 pm, Carlos A. M. dos Santos 
wrote:
> >> On Mon, Sep 15, 2008 at 1:32 PM, Jung-uk Kim <jkim_at_freebsd.org>
> >
> > wrote:
> >> > On Monday 15 September 2008 05:22 am, Oliver Fromme wrote:
> >> >> Carlos A. M. dos Santos wrote:
> >> >>  > Xin LI wrote:
> >> >>  > > Carlos A. M. dos Santos wrote:
> >> >>  > > > Several PRs were closed based on the argument that
> >> >>  > > > FreeBSD/amd64 cannot call to the VESA BIOS. XFree86
> >> >>  > > > solved this problem by means of the INT10 module. I
> >> >>  > > > believe that it would be possible to do the same on
> >> >>  > > > the FreeBSD kernel.
> >> >>  > > >
> >> >>  > > > Is there any ongoing effort to enable the VESA kernel
> >> >>  > > > moule on non-i386 platform? Is there any particular
> >> >>  > > > difficulty for doing this, besides depending on VM86?
> >> >>  > >
> >> >>  > > According to VESA's VBE 3.0 standard, there is a
> >> >>  > > "Protected Mode Entry Point" [optionally] provided by
> >> >>  > > BIOS, which OS or application is supposed to copy to a
> >> >>  > > place where it is writable.  The code there would be
> >> >>  > > written in 16-bit protected mode.  Therefore I think
> >> >>  > > it's do-able...
> >> >>  > >
> >> >>  > > http://www.vesa.org/public/VBE/vbe3.pdf
> >> >>  >
> >> >>  > I'm reading the specification and digging at the code of
> >> >>  > the X server and the X VESA driver. Look promising.
> >> >>
> >> >> Don't hold your breath.  Peter explained that this is more
> >> >> involved than it seems at first glance:
> >> >>
> >> >> http://lists.freebsd.org/pipermail/freebsd-amd64/2005-October
> >> >>/00 637 6.html
> >> >>
> >> >> Here's a quote:
> >> >>   |  [FreeBSD's VESA code] is trying to use bios calls to
> >> >>   | change the modes.  This is something a 64 bit kernel
> >> >>   | cannot do.  To make this work, one would have to
> >> >>   | trampoline out of 64 bit mode and into 32 bit mode, then
> >> >>   | do the vm86 or bios32() calls.  This is more work than it
> >> >>   | might appear at first because you have to deal with
> >> >>   | interrupts.  One would have to write a 32 bit mini-kernel
> >> >>   | that can accept interrupts and traps, trampoline to 64
> >> >>   | bit mode, handle them, then return, switching back to 32
> >> >>   | bit mode.  All with page tables etc. And of course you
> >> >>   | have to do extra data copying and have a way to describe
> >> >>   | it to the API.
> >> >>
> >> >> By the way, It doesn't matter whether you use the VESA
> >> >> BIOS' real-mode functions or the protected-mode functions
> >> >> (which exist since VBE 2.0, not only 3.0).  From the view
> >> >> of an amd64 kernel it doesn't make a difference.
> >> >>
> >> >> Another way would be to write a 32bit x86 instruction
> >> >> emulator (similar to what programs like qemu or bochs do),
> >> >> so you can execute the VESA functions within an emulated
> >> >> virtual machine that programs the VGA hardware registers.
> >> >> This isn't exactly trivial either.  Note that there are
> >> >> already such emulators, but I'm not aware of a BSD-licensed
> >> >> one that could be included in the FreeBSD kernel without
> >> >> problems.
> >> >
> >> > doscmd(1) had a rudimentary 16-bit CPU emulation:
> >> >
> >> > http://www.freebsd.org/cgi/cvsweb.cgi/projects/doscmd/
> >> > http://www.freebsd.org/cgi/cvsweb.cgi/projects/doscmd/cpu.c
> >>
> >> No change in the last 4 years. Is there anybody responsible for
> >> it these days?
> >
> > doscmd(1) was removed from base and moved to ports:
> >
> > http://www.freebsd.org/cgi/cvsweb.cgi/ports/emulators/doscmd/
> >
> > Don't get me wrong, BTW.  It does not work on amd64.  I just
> > brought it up because we *may* be able to do a hybrid approach
> > [...]
>
> Depends on vm86 too.
>
> > [...] as Linux DOSEMU does:
> >
> > http://en.wikipedia.org/wiki/DOSEMU
> >
> > "Virtual 8086 mode is not available in x86-64 long mode, so
> > DOSEMU includes an 8086 processor emulator for use with 16-bit
> > applications."
>
> Wrong license.
>
> > Also, Linux people actually developed vm86 calls for amd64:
> >
> > http://v86-64.sourceforge.net/
>
> It is a Linux kernel patch, doubtfully applicable to FreeBSD
> without a lot of hassle. I'm also concerned about the license
> terms.

No, I am not saying we can reuse any of these.  I was merely saying we 
could do something similar, conceptually. :-)

Jung-uk Kim