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Re: [PATCH 01/20] Hexagon HVX (target/hexagon) README

From: Rob Landley
Subject: Re: [PATCH 01/20] Hexagon HVX (target/hexagon) README
Date: Mon, 26 Jul 2021 03:54:43 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

On 7/26/21 2:57 AM, Rob Landley wrote:
> Anyway... it doesn't look like qemu-system-hexagon (softmmu) its currently in
> vanilla qemu? Is there a public fork that has this somewhere?

I did a little wild flailing to get ./configure to give me a qemu-system-hexagon
option (patch attached), I.E. just enough to get meson to shut up and quite
possibly still missing something important. (Is this python? It looks kind of
like python.)

Unfortunately after liberally cribbing from the cris architecture (which seems
like the simplest one) I'm left with several new C files to implement, all
currently zero length in the patch:


(In theory there's a "none" board on all the current qemu-system architectures,
but I've never figured out what to DO with those...)

All this raises two problems:

1) I dunno how the hexagon mmu works. (I can presumably read the kernel code and
reverse engineer what that's looking for, but it would be really nice not to
_have_ to?)

2) What's a comet board? (Memory layout? I/O devices? I guess all I need for
serial console on initramfs is a contiguous block of DRAM, timer interrupt to
drive the scheduler, and a serial port. I keep thinking there should be a way to
tell the "none" board to add that stuff from the command line... but dunno how.
"map DRAM here". "add this clock hardware at here". "add this kind of serial
port at here." "call elf_load on this file and start executing at its entry

3) Reading the arch/hexagon kernel stuff ala "so what IS in a comet board"...
CONFIG_HEXAGON_COMET is only ever used to guard one #define in a header file:

  arch/hexagon/include/asm/timer-regs.h:#define RTOS_TIMER_REGS_ADDR

Which is then used to initialize structure members in arch/hexagon/kernel/time.c
without any sort of guard there, and no it isn't #defined to 0 by default
anywhere I can see? And of course obj-y += time.o in
arch/hexagon/kernel/Makefile has no config guard there either. So if it wasn't
set, the build would break. And that's currently all the symbol does?

Anyway, I still hope somebody else has already done most of this in a git tree
somewhere. :)


Attachment: hexagon-softmmu-skeleton.patch
Description: Text Data

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