Hi Angelo,
On Fri, Sep 1, 2017 at 12:38 AM, Angelo Dureghello <angelo@xxxxxxxx> wrote:
Hi Greg and all,
did some additional study and tests.
Actually i cannot find any simpler patch, i just adjusted it a
bit. I believe this patch will work on your cpu with 0-based
memoryas well.
I attach it for your comments.
I think your issue is caused by arch/m68k/include/asm/page_offset.h:
#if defined(CONFIG_RAMBASE)
#define PAGE_OFFSET_RAW CONFIG_RAMBASE
#elif defined(CONFIG_SUN3)
#define PAGE_OFFSET_RAW 0x0E000000
#else
#define PAGE_OFFSET_RAW 0x00000000
#endif
and arch/m68k/Kconfig.machine:
if !MMU || COLDFIRE
config RAMBASE
hex "Address of the base of RAM"
default "0"
So on MC680[2346]0 with MMU (and ignoring Sun-3, which is special),
PAGE_OFFSET == PAGE_OFFSET_RAW == 0.
On Greg's zero-based Coldfire with MMU, CONFIG_RAMBASE is zero, and thus
PAGE_OFFSET is also zero.
On your board CONFIG_RAMBASE is non-zero, hence PAGE_OFFSET is also non-zero,
and thus you have to compensate for that, cfr. your second patch.
Does it work if you force PAGE_OFFSET_RAW to zero?
If yes, we either need:
--- a/arch/m68k/include/asm/page_offset.h
+++ b/arch/m68k/include/asm/page_offset.h
@@ -1,6 +1,6 @@
/* This handles the memory map.. */
-#if defined(CONFIG_RAMBASE)
+#if !defined(CONFIG_MMU)
#define PAGE_OFFSET_RAW CONFIG_RAMBASE
#elif defined(CONFIG_SUN3)
#define PAGE_OFFSET_RAW 0x0E000000
or
--- a/arch/m68k/Kconfig.machine
+++ b/arch/m68k/Kconfig.machine
@@ -325,6 +325,7 @@ comment "RAM configuration"
config RAMBASE
hex "Address of the base of RAM"
+ depends on MMU
default "0"
help
Define the address that RAM starts at. On many platforms this is
@@ -334,6 +335,7 @@ config RAMBASE
config RAMSIZE
hex "Size of RAM (in bytes), or 0 for automatic"
+ depends on MMU
default "0x400000"
help
Define the size of the system RAM. If you select 0 then the
depending on whether anything else in the Coldfire code needs RAMBASE.
Mainly what is not clear is what is the "m68k_fixup" needed.
I am interested eventually to know where the idea of that fixup
come from. The fixup seems should be module-related only, but
actually is called from each __pa() and __va(), so i am bit
conufsed, it seems also a kind of fixup (assembly replacement
at runtime) that i don't find in other archs.
commit fbe9c9612930e0604dc99ef2da7e063fa3278817
Author: Roman Zippel <zippel@xxxxxxxxxxxxxx>
Date: Thu May 31 00:40:50 2007 -0700
m68k: runtime patching infrastructure
Add the basic infrastructure to allow runtime patching of kernel and modules
to optimize a few functions with parameters, which are only calculated once
during bootup and are otherwise constant. Use this for the
conversion between
virtual and physical addresses.
So it's a micro-optimization for virt/phys conversions, to avoid the extra
load of the offset to add/subtract.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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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