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[MIPS] Request for the 'mips_cache_lock()' removal 

The initial intension of having mips_cache_lock() was to use the cache
as memory for temporary stack use so that a C environment can be set up
as early as possible.

But now mips_cache_lock() follow lowlevel_init(). We've already have the
real memory initilaized at this point, therefore we could/should use it.
No reason to lock at all.

Other problems:

Cache locking is not consistent across MIPS implementaions. Some imple-
mentations don't support locking at all. The style of locking varies -
some support per line locking, others per way, etc. Some parts use bits
in status registers instead of cache ops. Current mips_cache_lock() is
not necessarily general-purpose.

And this is worthy of special mention; once U-Boot/MIPS locks the lines,
they are never get unlocked, so the code relies on whatever gets loaded
after U-Boot to re-initialize the cache and clear the locks. We're sup-
posed to have CFG_INIT_RAM_LOCK and unlock_ram_in_cache() implemented,
but leave the situation as it is for a long time.

For these reasons, I proposed the removal of mips_cache_lock() from the
global start-up code.

This patch adds CFG_INIT_RAM_LOCK_MIPS to make existing users aware that
*things have changed*. If he wants the same behavior as before, he needs
to have CFG_INIT_RAM_LOCK_MIPS in his config file.

If we don't have any regression report through several releases, then
we'll remove codes entirely.

Signed-off-by: Shinya Kuribayashi <skuribay@ruby.dti.ne.jp>
Acked-by: Andrew Dyer <amdyer@gmail.com>
This commit is contained in:
Shinya Kuribayashi 2008-03-25 11:39:29 +09:00
parent 0d48926c87
commit e1390801a3
2 changed files with 4 additions and 0 deletions
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2
cpu/mips/cache.S
View File

@ -238,6 +238,7 @@ dcache_disable:
.end dcache_disable
#ifdef CFG_INIT_RAM_LOCK_MIPS
/*******************************************************************************
*
* mips_cache_lock - lock RAM area pointed to by a0 in cache.
@ -263,3 +264,4 @@ mips_cache_lock:
j ra
.end mips_cache_lock
#endif /* CFG_INIT_RAM_LOCK_MIPS */

2
cpu/mips/start.S
View File

@ -267,10 +267,12 @@ reset:
/* Set up temporary stack.
*/
#ifdef CFG_INIT_RAM_LOCK_MIPS
li a0, CFG_INIT_SP_OFFSET
la t9, mips_cache_lock
jalr t9
nop
#endif
li t0, CFG_SDRAM_BASE + CFG_INIT_SP_OFFSET
la sp, 0(t0)