Re: Linux 3.10-2-m68k FPU support
On Sun, Oct 20, 2013 at 10:04 AM, Ingo Jürgensmann
<ij@2013.bluespice.org> wrote:
> Am 20.10.2013 um 01:46 schrieb Thorsten Glaser <tg@mirbsd.de>:
>> Geert Uytterhoeven dixit:
>>> FPU emulation should be fine, AFAIK (never used it myself, though).
>> Michael Schmitz dixit:
>>> The docs are quite clearly out of date. From memory, there may be the odd FPU
>> […]
>>> Seeing as this code is crucial, I'd opt for putting it back in, and finding
>> These two statements are “it should be fine but I don’t really know”
>> and “this is important so put it back in, but I don’t remember details”.
>> Together with what *is* currently in the documentation, this is
>> *not* reassuring, and I *know* that FPU emulation code all across
>> OSes (kernels and not) is a sore topic (even being kicked from
>> some of them).
>> My request for a clear statement still stands.
>
> ... and there's the statement from Adrian that it works without problems so far.
Indeed. The emulation may be incomplete, but for most people it's useable,
and definitely better than nothing.
Furthermore, for people running Debian on their FPU-less machines before,
the new kernel image is definitely a regression, so it warrants re-enabling
FPU emulation to fix this.
>> On the other hand, I cannot help but wonder how well it compares
>> to whatever ARAnyM passes as FPU. I know ARAnyM doesn’t handle the
>> 80/64bit precision switch at all (which is why we opted to not use
>> that for Python), but I smell some sort of knob here… if the knob
>> can be used to tweak between speed and correctness, I’d opt for
>> correctness. (OK, BSD user speaking.) It’d probably be faster at
>> runtime to fix ARAnyM instead but that’s a different upstream.
>
> Hmmm... if Aranym is the problematic part in this story, then Aranym should be changed to reflect how real hardware works. There were a lot of Amiga accelerator cards built & sold without an FPU, although most of them have a socket for a 68881/2. It's been a matter of money back then and FPUs weren't widely used under AmigaOS. Except when you were doing 3D graphics and such. But then again one had no A1200 for this purpose but a A2/3/4000 with 68040 or 68060s. But the majority of sold accelerator cards, I believe, was for A1200 and 68030 just for the reason of money.
>
> At least I opt for providing a FPU enabled kernel. It doesn't need to be the default kernel, but we shouldn't exclude a number of users just because an emulator might have problems with FPU emulation. It's easier to change that piece of software than to change the piece of hardware.
Nevertheless, FPU emulation in ARAnyM is something different. ARAnyM
is an emulator that emulates a full 68040, incl. FPU. So as far as the Linux
kernel is concerned, no in-kernel FPU emulation is involved.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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