rockchip: enable timer7 on rk3288 platforms for broken bootloaders

timer7 supplies the architected timer and thus as has to run when
the system clocksource and clockevents drivers are registered.

While it should be the responsibility of the bootloader to do this,
older uboot variants for the rk3288 did not do this.

Therefore add a snippet for those, enabling the timer early in the
kernel.

arch/arm/mach-rockchip/rockchip.c

@@ -24,6 +24,36 @@
 #include <asm/hardware/cache-l2x0.h>
 #include "core.h"
 
+#include <linux/clocksource.h>
+#include <linux/clk-provider.h>
+
+static void __init rockchip_timer_init(void)
+{
+	of_clk_init(NULL);
+
+	if (of_machine_is_compatible("rockchip,rk3288")) {
+		void __iomem *reg_base;
+
+		/* enable timer7 for core */
+		pr_warn("rockchip: enabling rk3288-timer7 workaround\n");
+		reg_base = ioremap(0xFF810000, 0x4000);
+		if (reg_base) {
+			writel_relaxed(0, reg_base + 0x30);
+			dsb();
+			writel_relaxed(0xFFFFFFFF, reg_base + 0x20);
+			writel_relaxed(0xFFFFFFFF, reg_base + 0x24);
+			dsb();
+			writel_relaxed(1, reg_base + 0x30);
+			dsb();
+			iounmap(reg_base);
+		} else {
+			pr_err("rockchip: could not map timer7 registers\n");
+		}
+	}
+
+	clocksource_of_init();
+}
+
 static void __init rockchip_dt_init(void)
 {
 	of_platform_populate(NULL, of_default_bus_match_table, NULL, NULL);
@@ -42,6 +72,8 @@ static const char * const rockchip_board_dt_compat[] = {
 DT_MACHINE_START(ROCKCHIP_DT, "Rockchip Cortex-A9 (Device Tree)")
 	.l2c_aux_val	= 0,
 	.l2c_aux_mask	= ~0,
+	.init_time	= rockchip_timer_init,
+	.init_machine	= rockchip_dt_init,
 	.dt_compat	= rockchip_board_dt_compat,
 	.init_machine	= rockchip_dt_init,
 MACHINE_END