arm: socfpga: misc: Fix warm reset

Write necessary magic value into the Warm Boot from ON-Chip RAM
group Enable register to enable Warm reset support. Instead of
doing this in the reset_cpu() function, we do it in arch early
init to avoid breaking old kernel code which expects this magic
value to be already written into this register.

This magic is originally excavated from common/spl/spl.c in the
u-boot port from altera, where this value was written just before
the SPL jumped to actual U-Boot in the RAM.

Signed-off-by: Marek Vasut <marex@denx.de>

arch/arm/mach-socfpga/misc.c

@@ -194,6 +194,16 @@ static uint32_t iswgrp_handoff[8];
 int arch_early_init_r(void)
 {
 	int i;
+
+	/*
+	 * Write magic value into magic register to unlock support for
+	 * issuing warm reset. The ancient kernel code expects this
+	 * value to be written into the register by the bootloader, so
+	 * to support that old code, we write it here instead of in the
+	 * reset_cpu() function just before reseting the CPU.
+	 */
+	writel(0xae9efebc, &sysmgr_regs->romcodegrp_warmramgrp_enable);
+
 	for (i = 0; i < 8; i++)	/* Cache initial SW setting regs */
 		iswgrp_handoff[i] = readl(&sysmgr_regs->iswgrp_handoff[i]);