x86_64 BSP as GSOC2016 project

[Joel Sherrill]

On Feb 9, 2016 10:37 PM, "Saket Sinha" <saket.sinha89 at gmail.com> wrote:
>
> Hi Joel,
>
> Thanks for your inputs.
>
>
>
> On Wed, Feb 10, 2016 at 1:06 AM, Joel Sherrill <joel at rtems.org> wrote:
> >
> >
> > On Tue, Feb 9, 2016 at 12:08 PM, Saket Sinha <saket.sinha89 at gmail.com>
> > wrote:
> >>
> >> Hi,
> >>
> >> I think this is early for this but I need to enquire if x86_64_BSP (
> >> https://devel.rtems.org/wiki/Developer/Projects/Open/x86_64_BSP )
> >> could be taken as a GSOC project this year.
> >>
> >
> > Yes. Assuming you mean the x86_64 bit port and accompanying BSP.
> >
> > If you noticed my post yesterday, we have tripped across a new embedded
PC
> > without legacy PCI BIOS support.
> >
>
> Could you provide the link. I am not able to locate it on mailing list
> or your blog.

I only posted a question this week had anyone attempted to use RTEMS on a
PC without legacy BIOS. I think the answer is no.

I have done a little searching for how to use the newer UEFI services to
replace those we use the video and PCI but so far have only found high
level information.

Sorry. This one is a known need with only early research. I was going to
dig into the FreeBSD source next.

> > Beyond the obvious port, for the purposes of your effort, there are
> > a couple of bugs and some modernization needed by the pc386 BSP which
> > you will likely have to address.
> >
> > + PCI BIOS uses legacy support. Needs to support new and old for 32-bit
> > and new only for 64 bit.
> > + Better APIC support. pc386 uses legacy PIC and some LPIC for SMP.
> > Probably Ok for both 32 and 64 bit to support APIC only.
> > + i386 does not have Thread Local Support. Both should have it.
> > + i386 has a ticket for SMP synchronization during context switch.
> > The code does not use atomics. Should be fixed and x86_64 follow the
> > correct pattern.
> >
>
> So now my question is that could these be solved on an emulator like
> qemu-x86, atleast for an initial POC ?
> I mean is a x86_64 hardware required for it( though I have a Minnowmax
board.)
>

I think qemu can be used for all of this. You can certainly do the APIC
support without addressing the legacy video and PCI BIOS.

Similar for the TLS and SMP issue.

I believe the entire thing could be brought up and debugged on qemu with
checkouts on real HW. Either the Minnow or even a desktop PC with the right
BIOS settings. None of this is particularly new. APIC dates back at least a
decade.

>
> > Basically x86_64 should assume a modern (non-legacy) PC and pc386
> > needs updating to support newer systems. Common hardware platform
> > so hopefully the software is standard.
> >
> > I was going to write this up as a "PC386 Modernization" Project but some
> > of it makes sense as a side-effect of your project. That project idea
also
> > included killing AT bus NICs which you wouldn't have any reason to get
> > near.
> >
> > You need a subtask list (e.g. todo list) and we need to help you flesh
it
> > out. I only hit a few non-obvious highlights.
> >
>
> Let me know how to dig deeper on this. Looking at the code, right  but
> than exactly what sections ?
>

libbsp/shared/i386/pci is the current legacy PCI code.

The IRQ code should also be under shared.

I will have to feel to see where the video probe that is failing is located.

The nice thing is that each of these three can be completed in the context
of the current BSP.

> Regards,
> Saket Sinha
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