On Thu, 25 Aug 2005, Pete Popov wrote:
> This is an experimental (though tested) patch for early ioremap support
> on mips, before mem_init runs. Something like this is only needed on
> certain SoCs that have all of their I/O on high addresses such that they
> can't me ioremapped through kseg1.
Hmm, wouldn't a temporary large page and a wired TLB entry be an easier
solution? Somebody designing these SoCs must have taken such an approach
into account when deciding to put I/O devices outside the space that's
directly accessible through unmapped spaces, so I'd expect them all to be
reachable in a single page of the largest size supported by a given
implementation. Especially as not all software is expected to implement
fully-featured page management. This entry would of course be no longer
available after the final paging setup (TLBs tend to be too small for
entries to be wasted).
> I think the CONFIG_64 stuff needs to removed since we don't need it. The
> patch was tested on a MIPS32 CPU only. Some of the significant changes:
Well, MIPS64 has XPHYS, so there is no need for going through paging for
ioremap() at all.
> - trap_init() became early_trap_init() since too much stuff happens
> there that is needed to support early ioremap. The old trap_init() is
> now empty.
That just provides a strong suggestion considering an alternative
approach, such as one proposed above is not a bad idea -- this changes the
order subsystems are initialized for the MIPS platform, which makes it
different from all the others and therefore problematic.
> - added plat_setup_late() call. All ports would need to add that call,
> or at least a placeholder. Early ioremap is possible only at that point.
> However, most of the code in each plat_setup() can be moved to
> plat_setup_late()
Which means it should rather be a function pointer initialized somewhere
earlier, possibly in plat_setup() and then:
static void __init null_plat_setup_late(void) { }
void (*plat_setup_late)(void) __initdata = null_plat_setup_late;
[...]
plat_setup_late()
or:
void (*plat_setup_late)(void);
[...]
if (plat_setup_late)
plat_setup_late()
or something like that.
Maciej
