Hi Michael,
On Tue, May 22, 2018 at 12:51 PM, Michael Schmitz <[email protected]> wrote:
> Am 22.05.2018 um 20:18 schrieb Geert Uytterhoeven:
>> On Mon, May 14, 2018 at 1:10 PM, Michael Schmitz <[email protected]>
>> wrote:
>>> Comment on whether the gap size should be considered in looking for a
>>> suitable address to place the next mapping in get_io_area() would be
>>> welcome.
>>
>> At first sight (and looking in full-history-linux git history), I see no
>> reason for the gap. I'd assume having a block with address and size aligned
>> to 256 KiB (which the caller already takes care of: IO_SIZE is 256 KiB if
>> 020/030 support is enabled) should be sufficient to use early termination
>> tables.
>
> My guess is that someone wanted to catch out of bounds accesses by
> leaving the unmapped areas in between ioremapped 256 kB chunks. The
> unmapped gaps must 256 kB as well to avoid disturbing the alignment.
>
> The adjustment for gap size was dropped sometime between 2.4.30 and
> 2.6.18. At the same time, a comment in get_io_area was removed that
> stated 'leave a gap of IO_SIZE'. I haven't looked at the full history to
> find out who removed that comment (and the adjustment).
I can't seem to find the addition/removal of that comment (checked
full-history-linux and the old m68k-linux CVS)?
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
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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