Fix SP804 delay timer on FVP

This patch fixes several issues with the SP804 delay timer on FVP:

* By default, the SP804 dual timer on FVP runs at 32 KHz. In order
  to run the timer at 35 MHz (as specified in the FVP user manual)
  the Overwrite bit in the SP810 control register must be set.

* The CLKMULT and CLKDIV definitions are mixed up:

      delta(us) = delta(ticks) * T(us) = delta(ticks) / f(MHz)

  From the delay function:

      delta_us = (delta * ops->clk_mult) / ops->clk_div;

  Matching both expressions:

      1 / f(MHz) = ops->clk_mult / ops->clk_div

  And consequently:

      f(MHz) = ops->clk_div / ops->clk_mult

  Which, for a 35 MHz timer, translates to:

      ops->clk_div = 35
      ops->clk_mult = 1

* The comment in the delay timer header file has been corrected:
  The ratio of the multiplier and the divider is the clock period
  in microseconds, not the frequency.

Change-Id: Iffd5ce0a5a28fa47c0720c0336d81b678ff8fdf1

include/drivers/delay_timer.h

@@ -38,7 +38,7 @@
  * The driver must be initialized with a structure that provides a
  * function pointer to return the timer value and a clock
  * multiplier/divider. The ratio of the multiplier and the divider is
- * the clock frequency in MHz.
+ * the clock period in microseconds.
  ********************************************************************/
 
 typedef struct timer_ops {

include/plat/arm/board/common/v2m_def.h

@@ -112,6 +112,13 @@
 #define V2M_SP804_TIMER0_BASE		0x1C110000
 #define V2M_SP804_TIMER1_BASE		0x1C120000
 
+/* SP810 controller */
+#define V2M_SP810_BASE			0x1c020000
+#define V2M_SP810_CTRL_TIM0_SEL		(1 << 15)
+#define V2M_SP810_CTRL_TIM1_SEL		(1 << 17)
+#define V2M_SP810_CTRL_TIM2_SEL		(1 << 19)
+#define V2M_SP810_CTRL_TIM3_SEL		(1 << 21)
+
 #define V2M_MAP_FLASH0_RW		MAP_REGION_FLAT(V2M_FLASH0_BASE,\
 						V2M_FLASH0_SIZE,	\
 						MT_DEVICE | MT_RW | MT_SECURE)

plat/arm/board/fvp/fvp_bl2_setup.c

@@ -28,6 +28,7 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <mmio.h>
 #include <plat_arm.h>
 #include <sp804_delay_timer.h>
 #include <v2m_def.h>
@@ -47,6 +48,10 @@ void bl2_platform_setup(void)
 {
 	arm_bl2_platform_setup();
 
+	/* Enable the clock override for SP804 timer 0, which means that no
+	 * clock dividers are applied and the raw (35 MHz) clock will be used */
+	mmio_write_32(V2M_SP810_BASE, FVP_SP810_CTRL_TIM0_OV);
+
 	/* Initialize delay timer driver using SP804 dual timer 0 */
 	sp804_timer_init(V2M_SP804_TIMER0_BASE,
 			SP804_TIMER_CLKMULT, SP804_TIMER_CLKDIV);

plat/arm/board/fvp/fvp_def.h

@@ -96,8 +96,14 @@
 #define PWRC_BASE			0x1c100000
 
 /* FVP SP804 timer frequency is 35 MHz*/
-#define SP804_TIMER_CLKMULT		35
-#define SP804_TIMER_CLKDIV		1
+#define SP804_TIMER_CLKMULT		1
+#define SP804_TIMER_CLKDIV		35
+
+/* SP810 controller. FVP specific flags */
+#define FVP_SP810_CTRL_TIM0_OV		(1 << 16)
+#define FVP_SP810_CTRL_TIM1_OV		(1 << 18)
+#define FVP_SP810_CTRL_TIM2_OV		(1 << 20)
+#define FVP_SP810_CTRL_TIM3_OV		(1 << 22)
 
 /*******************************************************************************
  * GIC-400 & interrupt handling related constants