On Tue, May 19, 2015 at 05:12:56PM +0100, Russell King wrote:

All ARMv5 and older CPUs invalidate their caches in the early assembly
setup function, prior to enabling the MMU.  This is because the L1
cache should not contain any data relevant to the execution of the
kernel at this point; all data should have been flushed out to memory.

This requirement should also be true for ARMv6 and ARMv7 CPUs - indeed,
these typically do not search their caches when caching is disabled (as
it needs to be when the MMU is disabled) so this change should be safe.

ARMv7 allows there to be CPUs which search their caches while caching is
disabled, and it's permitted that the cache is uninitialised at boot;
for these, the architecture reference manual requires that an
implementation specific code sequence is used immediately after reset
to ensure that the cache is placed into a sane state.  Such
functionality is definitely outside the remit of the Linux kernel, and
must be done by the SoC's firmware before _any_ CPU gets to the Linux
kernel.

Changing the data cache clean+invalidate to a mere invalidate allows us
to get rid of a lot of platform specific hacks around this issue for
their secondary CPU bringup paths - some of which were buggy.

Signed-off-by: Russell King <redacted>
---

[...]

 arch/arm/mach-tegra/Makefile          |  2 +-
 arch/arm/mach-tegra/headsmp.S         | 12 ------------
 arch/arm/mach-tegra/reset.c           |  2 +-
 arch/arm/mach-tegra/reset.h           |  1 -

[...]

Russell,

I saw a couple of conflicts trying to apply this to v4.1-rc1..v4.1-rc4
or any of recent linux-next versions. I ended up applying this on top of
your for-next branch and tested using that. The conflicts seem very
minor and a test merge of Tegra's for-next branch resolved this fine. A
test merge of next-20150520 shows one conflict in mach-socfpga/core.h,
but it's a trivial one to resolve.

Anyway, the patch seems to work fine on TrimSlice (Tegra20), Beaver
(Tegra30), Dalmore (Tegra114) and Jetson TK1 (Tegra124). Tested on
Paul's boot farm:

Tested-by: Thierry Reding <redacted>
Acked-by: Thierry Reding <redacted>

Paul, thanks for setting up the boot test infrastructure, this saved me
a lot of time.

Thierry
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