clocksource: convert MXS timrotv2 to 32-bit down counting clocksource

Convert the MXS timrotv2 32-bit down counting clocksource to the
generic clocksource infrastructure.

Cc: Sascha Hauer <[e-mail]>
Acked-by: Shawn Guo <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

arch/arm/Kconfig

···
 	select GENERIC_CLOCKEVENTS
 	select ARCH_REQUIRE_GPIOLIB
 	select CLKDEV_LOOKUP
+	select CLKSRC_MMIO
 	help
 	  Support for Freescale MXS-based family of processors
 

arch/arm/mach-mxs/timer.c

···
 			& 0xffff0000) >> 16);
 }
 
-static cycle_t timrotv2_get_cycles(struct clocksource *cs)
-{
-	return ~__raw_readl(mxs_timrot_base + HW_TIMROT_RUNNING_COUNTn(1));
-}
-
 static int timrotv1_set_next_event(unsigned long evt,
 					struct clock_event_device *dev)
 {
···
 static struct clocksource clocksource_mxs = {
 	.name		= "mxs_timer",
 	.rating		= 200,
-	.read		= timrotv2_get_cycles,
-	.mask		= CLOCKSOURCE_MASK(32),
+	.read		= timrotv1_get_cycles,
+	.mask		= CLOCKSOURCE_MASK(16),
 	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
···
 {
 	unsigned int c = clk_get_rate(timer_clk);
 
-	if (timrot_is_v1()) {
-		clocksource_mxs.read = timrotv1_get_cycles;
-		clocksource_mxs.mask = CLOCKSOURCE_MASK(16);
-	}
-
-	clocksource_register_hz(&clocksource_mxs, c);
+	if (timrot_is_v1())
+		clocksource_register_hz(&clocksource_mxs, c);
+	else
+		clocksource_mmio_init(mxs_timrot_base + HW_TIMROT_RUNNING_COUNTn(1),
+			"mxs_timer", c, 200, 32, clocksource_mmio_readl_down);
 
 	return 0;
 }