ARM: 6376/1: plat-nomadik: MTU: Change prescaler limit and comment updates

The prescaler 16 is now used only when the timer runs at 32 MHz
or more. Some comment updates as well.

Acked-by: Alessandro Rubini <rubini@unipv.it>
Signed-off-by: Jonas Aaberg <jonas.aberg@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 10 insertions, 7 deletions

diff --git a/arch/arm/plat-nomadik/timer.c b/arch/arm/plat-nomadik/timer.c
index d673888af18e..aedf9c1d645e 100644
--- a/arch/arm/plat-nomadik/timer.c
+++ b/arch/arm/plat-nomadik/timer.c
@@ -1,5 +1,5 @@
 /*
- *  linux/arch/arm/mach-nomadik/timer.c
+ *  linux/arch/arm/plat-nomadik/timer.c
  *
  * Copyright (C) 2008 STMicroelectronics
  * Copyright (C) 2010 Alessandro Rubini
@@ -75,7 +75,7 @@ static void nmdk_clkevt_mode(enum clock_event_mode mode,
                 cr = readl(mtu_base + MTU_CR(1));
                 writel(0, mtu_base + MTU_LR(1));
                 writel(cr | MTU_CRn_ENA, mtu_base + MTU_CR(1));
-                writel(0x2, mtu_base + MTU_IMSC);
+                writel(1 << 1, mtu_base + MTU_IMSC);
                 break;
         case CLOCK_EVT_MODE_SHUTDOWN:
         case CLOCK_EVT_MODE_UNUSED:
@@ -131,7 +131,7 @@ void __init nmdk_timer_init(void)
 {
         unsigned long rate;
         struct clk *clk0;
-        u32 cr;
+        u32 cr = MTU_CRn_32BITS;
 
         clk0 = clk_get_sys("mtu0", NULL);
         BUG_ON(IS_ERR(clk0));
@@ -139,12 +139,15 @@ void __init nmdk_timer_init(void)
         clk_enable(clk0);
 
         /*
-         * Tick rate is 2.4MHz for Nomadik and 110MHz for ux500:
-         * use a divide-by-16 counter if it's more than 16MHz
+         * Tick rate is 2.4MHz for Nomadik and 2.4Mhz, 100MHz or 133 MHz
+         * for ux500.
+         * Use a divide-by-16 counter if the tick rate is more than 32MHz.
+         * At 32 MHz, the timer (with 32 bit counter) can be programmed
+         * to wake-up at a max 127s a head in time. Dividing a 2.4 MHz timer
+         * with 16 gives too low timer resolution.
          */
-        cr = MTU_CRn_32BITS;;
         rate = clk_get_rate(clk0);
-        if (rate > 16 << 20) {
+        if (rate > 32000000) {
                 rate /= 16;
                 cr |= MTU_CRn_PRESCALE_16;
         } else {