[PATCH] ARM: v7 setup function should invalidate L1 cache

On Fri, May 22, 2015 at 9:36 AM, Geert Uytterhoeven
[off-list ref] wrote:

On Tue, May 19, 2015 at 6:12 PM, Russell King
[off-list ref] wrote:

quoted

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>

For various shmobile:
  - sh73a0/kzm9g
  - r8a7740/armadillo
  - r8a73a4/ape6evm
  - r8a7791/koelsch

Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

FWIW, I have the feeling this has a slight influence on boot reliability on
two of my boards:
  - r8a7740/armadillo, which is known to suffer from a cache-related bug in
    its bootloader, seems to have a higher change of booting successfully on
    cold boot,
  - sh73a0/kzm9g, which has known cache-issues with secondary CPU boot up,
    seems to have a lower chance of booting successfully.

No time to spend all week turning this into a statistical significant test
project... The reset button is my friend...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

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