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Date:   Sat, 9 Apr 2022 11:59:57 +1000 (AEST)
From:   Finn Thain <fthain@linux-m68k.org>
To:     Rob Landley <rob@landley.net>
cc:     Greg Ungerer <gerg@linux-m68k.org>,
        Daniel Palmer <daniel@0x0f.com>, Arnd Bergmann <arnd@arndb.de>,
        Christoph Hellwig <hch@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
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Subject: Re: [RFC PULL] remove arch/h8300
In-Reply-To: <8f9be869-7244-d92a-4683-f9c53da97755@landley.net>
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On Fri, 8 Apr 2022, Rob Landley wrote:

> On 4/5/22 08:07, Greg Ungerer wrote:
> > On 5/4/22 13:23, Daniel Palmer wrote:
> >> On Mon, 4 Apr 2022 at 22:42, Greg Ungerer <gerg@linux-m68k.org> wrote:
> >>> But we could consider the Dragonball support for removal. I keep it 
> >>> compiling, but I don't use it and can't test that it actually works. 
> >>> Not sure that it has been used for a very long time now. And I 
> >>> didn't even realize but its serial driver (68328serial.c) was 
> >>> removed in 2015. No one seems too have noticed and complained.
> >> 
> >> I noticed this and I am working on fixing it up for a new Dragonball 
> >> homebrew machine. I'm trying to add a 68000 machine to QEMU to make 
> >> the development easier because I'm currently waiting an hour or more 
> >> for a kernel to load over serial. It might be a few months.
> 
> I've been booting Linux on qemu-system-m68k -M q800 for a couple years 
> now? (The CROSS=m68k target of mkroot in toybox?)
> 
> # cat /proc/cpuinfo
> CPU:		68040
> MMU:		68040
> FPU:		68040
> Clocking:	1261.9MHz
> BogoMips:	841.31
> Calibration:	4206592 loops
> 
> It certainly THINKS it's got m68000...
> 

Most 68040 processor variants have a built-in MMU and the m68k "nommu" 
Linux port doesn't support them. The nommu port covers processors like 
68000, Dragonball etc. whereas the m68k "mmu" port covers 680x0 where x is 
one of 2,3,4,6 with MMU.

> $ qemu-system-m68k -cpu ?
> cfv4e
> m5206
> m5208
> m68000
> m68010
> m68020
> m68030
> m68040
> m68060
> any
> 
> (I'd love to get an m68k nommu system working but never sat down and 
> worked out a kernel .config qemu agreed to run, plus compiler and libc. 
> Musl added m68k support but I dunno if that includes coldfire?)
> 

I could never figure out how to boot a coldfire machine in qemu either. 
There was no documentation about that back when I attempted it but maybe 
things have improved since.

> >> It looked like 68328serial.c was removed because someone tried to 
> >> clean it up and it was decided that no one was using it and it was 
> >> best to delete it. My plan was to at some point send a series to fix 
> >> up the issues with the Dragonball support, revert removing the serial 
> >> driver and adding the patch that cleaned it up.
> > 
> > Nice. I will leave all the 68000/68328 code alone for now then.
> 
> The q800 config uses CONFIG_SERIAL_PMACZILOG. Seems to work fine?
> 

That driver would work on certain 68000 systems e.g. early Macs. (And IIRC 
someone did once boot a customized Linux kernel on a Mac SE...)