ARM: shmobile: rcar-gen2: Stop compiling headsmp-apmu on !SMP

As of commit cad160ed0a94927e ("ARM: shmobile: Convert file to use
cntvoff"), there's no non-SMP code left in headsmp-apmu.S.

Hence build the file for SMP only, and drop the no longer needed check
for CONFIG_SMP inside the file.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

ARM: shmobile: convert to SPDX identifier

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

ARM: shmobile: Convert file to use cntvoff

Now that a common function is available for CNTVOFF's
initialization, let's convert shmobile-apmu code to use
this function.

Signed-off-by: Mylène Josserand <mylene.josserand@bootlin.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>

ARM: shmobile: rcar-gen2: fix non-SMP build

A bugfix for the SMP case broke the build for the UP case:

arch/arm/mach-shmobile/headsmp-apmu.o: In function `shmobile_boot_apmu':
(.text+0x34): undefined reference to `secondary_startup'

The assembler file mixes code that is used for SMP with code
that we also need on a single-CPU build, so I'm leaving it
always enabled in the Makefile, but enclose the SMP code
in an #ifdef.

Fixes: fd45a136ff6 ("ARM: shmobile: rcar-gen2: Make sure CNTVOFF is initialized on CA7/15")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

ARM: shmobile: rcar-gen2: Make sure CNTVOFF is initialized on CA7/15

On Cortex-A7, the arch timer CNTVOFF register is uninitialized.
Ideally it should be initialized by the boot loader, but it isn't.

For the boot CPU, CNTVOFF is initialized by Linux since commit
9ce3fa6816c2fb59 ("ARM: shmobile: rcar-gen2: Add CA7 arch_timer
initialization for r8a7794").
For secondary CPU cores, no such initialization is done.

Hence when enabling SMP on r8a7794, the kernel log is spammed with:

WARNING: Underflow in clocksource 'arch_sys_counter' observed, time update ignored.
Please report this, consider using a different clocksource, if possible.
Your kernel is probably still fine.

As Marc Zyngier pointed out that Cortex-A15 and Cortex-A7 are similar with
respect to CNTVOFF, we have been very lucky this just worked on R-Car
Gen2 SoCs with Cortex-A15 cores.

To fix this:
- Move the existing inline asm code to initialize CNTVOFF to an
assembler source file (adding comments and replacing hardcoded
constants by definitions in the process), so it can be reused,
- Perform the initialization of CNTVOFF on the boot CPU (Cortex-A15 or
Cortex-A7) on all R-Car Gen2 and RZ/G1 parts,
- Wrap the standard secondary_startup() routine inside a routine which
initializes CNTVOFF.

Based on patches by Hisashi Nakamura in the BSP.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>