mfd: dbx500: Provide a more accurate smp_twd clock

The local timer clock is based on ARM subsystem clock. This patch
obtains a more exact value of that clock by reading PRCMU registers.
Using this increases the accuracy of the local timer events.
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rickard Andersson <rickard.andersson@stericsson.com>
Signed-off-by: Michel Jaouen <michel.jaouen@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/mfd/db8500-prcmu.c

@@ -418,6 +418,9 @@ static struct {
 
 static atomic_t ac_wake_req_state = ATOMIC_INIT(0);
 
+/* Functions definition */
+static void compute_armss_rate(void);
+
 /* Spinlocks */
 static DEFINE_SPINLOCK(prcmu_lock);
 static DEFINE_SPINLOCK(clkout_lock);
@@ -1013,6 +1016,7 @@ int db8500_prcmu_set_arm_opp(u8 opp)
 		(mb1_transfer.ack.arm_opp != opp))
 		r = -EIO;
 
+	compute_armss_rate();
 	mutex_unlock(&mb1_transfer.lock);
 
 	return r;
@@ -1612,6 +1616,7 @@ static unsigned long pll_rate(void __iomem *reg, unsigned long src_rate,
 	if ((branch == PLL_FIX) || ((branch == PLL_DIV) &&
 		(val & PRCM_PLL_FREQ_DIV2EN) &&
 		((reg == PRCM_PLLSOC0_FREQ) ||
+		 (reg == PRCM_PLLARM_FREQ) ||
 		 (reg == PRCM_PLLDDR_FREQ))))
 		div *= 2;
 
@@ -1661,6 +1666,39 @@ static unsigned long clock_rate(u8 clock)
 	else
 		return 0;
 }
+static unsigned long latest_armss_rate;
+static unsigned long armss_rate(void)
+{
+	return latest_armss_rate;
+}
+
+static void compute_armss_rate(void)
+{
+	u32 r;
+	unsigned long rate;
+
+	r = readl(PRCM_ARM_CHGCLKREQ);
+
+	if (r & PRCM_ARM_CHGCLKREQ_PRCM_ARM_CHGCLKREQ) {
+		/* External ARMCLKFIX clock */
+
+		rate = pll_rate(PRCM_PLLDDR_FREQ, ROOT_CLOCK_RATE, PLL_FIX);
+
+		/* Check PRCM_ARM_CHGCLKREQ divider */
+		if (!(r & PRCM_ARM_CHGCLKREQ_PRCM_ARM_DIVSEL))
+			rate /= 2;
+
+		/* Check PRCM_ARMCLKFIX_MGT divider */
+		r = readl(PRCM_ARMCLKFIX_MGT);
+		r &= PRCM_CLK_MGT_CLKPLLDIV_MASK;
+		rate /= r;
+
+	} else {/* ARM PLL */
+		rate = pll_rate(PRCM_PLLARM_FREQ, ROOT_CLOCK_RATE, PLL_DIV);
+	}
+
+	latest_armss_rate = rate;
+}
 
 static unsigned long dsiclk_rate(u8 n)
 {
@@ -1707,6 +1745,8 @@ unsigned long prcmu_clock_rate(u8 clock)
 		return pll_rate(PRCM_PLLSOC0_FREQ, ROOT_CLOCK_RATE, PLL_RAW);
 	else if (clock == PRCMU_PLLSOC1)
 		return pll_rate(PRCM_PLLSOC1_FREQ, ROOT_CLOCK_RATE, PLL_RAW);
+	else if (clock == PRCMU_ARMSS)
+		return armss_rate();
 	else if (clock == PRCMU_PLLDDR)
 		return pll_rate(PRCM_PLLDDR_FREQ, ROOT_CLOCK_RATE, PLL_RAW);
 	else if (clock == PRCMU_PLLDSI)
@@ -2693,6 +2733,7 @@ void __init db8500_prcmu_early_init(void)
 					 handle_simple_irq);
 		set_irq_flags(irq, IRQF_VALID);
 	}
+	compute_armss_rate();
 }
 
 static void __init init_prcm_registers(void)

drivers/mfd/dbx500-prcmu-regs.h

@@ -61,7 +61,8 @@
 #define PRCM_PLLARM_LOCKP_PRCM_PLLARM_LOCKP3	0x2
 
 #define PRCM_ARM_CHGCLKREQ	(_PRCMU_BASE + 0x114)
-#define PRCM_ARM_CHGCLKREQ_PRCM_ARM_CHGCLKREQ	0x1
+#define PRCM_ARM_CHGCLKREQ_PRCM_ARM_CHGCLKREQ	BIT(0)
+#define PRCM_ARM_CHGCLKREQ_PRCM_ARM_DIVSEL	BIT(16)
 
 #define PRCM_PLLARM_ENABLE	(_PRCMU_BASE + 0x98)
 #define PRCM_PLLARM_ENABLE_PRCM_PLLARM_ENABLE	0x1
@@ -140,6 +141,7 @@
 /* PRCMU clock/PLL/reset registers */
 #define PRCM_PLLSOC0_FREQ	   (_PRCMU_BASE + 0x080)
 #define PRCM_PLLSOC1_FREQ	   (_PRCMU_BASE + 0x084)
+#define PRCM_PLLARM_FREQ	   (_PRCMU_BASE + 0x088)
 #define PRCM_PLLDDR_FREQ	   (_PRCMU_BASE + 0x08C)
 #define PRCM_PLL_FREQ_D_SHIFT	0
 #define PRCM_PLL_FREQ_D_MASK	BITS(0, 7)

include/linux/mfd/dbx500-prcmu.h

@@ -136,6 +136,7 @@ enum prcmu_clock {
 	PRCMU_TIMCLK,
 	PRCMU_PLLSOC0,
 	PRCMU_PLLSOC1,
+	PRCMU_ARMSS,
 	PRCMU_PLLDDR,
 	PRCMU_PLLDSI,
 	PRCMU_DSI0CLK,