On 2014/1/22 21:27, Russell King - ARM Linux wrote:

On Wed, Jan 22, 2014 at 07:25:15PM +0800, Wang Nan wrote:

quoted

ARM's kdump is actually corrupted (at least for omap4460), mainly because of
cache problem: flush_icache_range can't reliably ensure the copied data
correctly goes into RAM.

Quite right too.  You're mistake here is thinking that flush_icache_range()
should push it to RAM.  That's incorrect.

flush_icache_range() is there to deal with such things as loadable modules
and self modifying code, where the MMU is not being turned off.  Hence, it
only flushes to the point of coherency between the I and D caches, and
any further levels of cache between that point and memory are not touched.
Why should it touch any more levels - it's not the function's purpose.

quoted

After mmu turned off and jump to the trampoline, kexec always failed due
to random undef instructions.

We already have code in the kernel which deals with shutting the MMU off.
An instance of how this can be done is illustrated in the soft_restart()
code path, and kexec already uses this.

One of the first things soft_restart() does is turn off the outer cache -
which OMAP4 does have, but this can only be done if there is a single CPU
running.  If there's multiple CPUs running, then the outer cache can't be
disabled, and that's the most likely cause of the problem you're seeing.

You are right, commit b25f3e1c (OMAP4/highbank: Flush L2 cache before disabling)
solves my problem, it flushes outer cache before disabling. I have tested it in
UP and SMP situations and it works (actually, omap4 has not ready to support kexec
in SMP case, I insert an empty cpu_kill() to make it work), so the first 2
patches are unneeded.

What about the 3rd one (ARM: allow kernel to be loaded in middle of phymem)?