davinci: support changing the clock rate in clock framework

clk_round_rate, clk_set_rate have been updated to handle dynamic
frequency changes.

The motivation behind the changes is to support dynamic CPU frequency
change.

davinci_set_pllrate() changes the PLL rate of a given PLL. This function
has been presented as a generic function though it has been tested only
on OMAP-L138 EVM. No other currently available DaVinci device will probably
use this function, but any future device specific changes will hopefully be
small enough to get taken care using a cpu_is_xxx() macro.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>

2 files changed, 119 insertions, 3 deletions

diff --git a/arch/arm/mach-davinci/clock.c b/arch/arm/mach-davinci/clock.c
index 6de1e3428f1f..09e0e1c00a59 100644
--- a/arch/arm/mach-davinci/clock.c
+++ b/arch/arm/mach-davinci/clock.c
@@ -19,6 +19,7 @@
 #include <linux/mutex.h>
 #include <linux/platform_device.h>
 #include <linux/io.h>
+#include <linux/delay.h>
 
 #include <mach/hardware.h>
 
@@ -99,17 +100,44 @@ long clk_round_rate(struct clk *clk, unsigned long rate)
         if (clk == NULL || IS_ERR(clk))
                 return -EINVAL;
 
+        if (clk->round_rate)
+                return clk->round_rate(clk, rate);
+
         return clk->rate;
 }
 EXPORT_SYMBOL(clk_round_rate);
 
+/* Propagate rate to children */
+static void propagate_rate(struct clk *root)
+{
+        struct clk *clk;
+
+        list_for_each_entry(clk, &root->children, childnode) {
+                if (clk->recalc)
+                        clk->rate = clk->recalc(clk);
+                propagate_rate(clk);
+        }
+}
+
 int clk_set_rate(struct clk *clk, unsigned long rate)
 {
+        unsigned long flags;
+        int ret = -EINVAL;
+
         if (clk == NULL || IS_ERR(clk))
-                return -EINVAL;
+                return ret;
 
-        /* changing the clk rate is not supported */
-        return -EINVAL;
+        spin_lock_irqsave(&clockfw_lock, flags);
+        if (clk->set_rate)
+                ret = clk->set_rate(clk, rate);
+        if (ret == 0) {
+                if (clk->recalc)
+                        clk->rate = clk->recalc(clk);
+                propagate_rate(clk);
+        }
+        spin_unlock_irqrestore(&clockfw_lock, flags);
+
+        return ret;
 }
 EXPORT_SYMBOL(clk_set_rate);
 
@@ -296,6 +324,86 @@ static unsigned long clk_pllclk_recalc(struct clk *clk)
         return rate;
 }
 
+/**
+ * davinci_set_pllrate - set the output rate of a given PLL.
+ *
+ * Note: Currently tested to work with OMAP-L138 only.
+ *
+ * @pll: pll whose rate needs to be changed.
+ * @prediv: The pre divider value. Passing 0 disables the pre-divider.
+ * @pllm: The multiplier value. Passing 0 leads to multiply-by-one.
+ * @postdiv: The post divider value. Passing 0 disables the post-divider.
+ */
+int davinci_set_pllrate(struct pll_data *pll, unsigned int prediv,
+                                        unsigned int mult, unsigned int postdiv)
+{
+        u32 ctrl;
+        unsigned int locktime;
+
+        if (pll->base == NULL)
+                return -EINVAL;
+
+        /*
+         *  PLL lock time required per OMAP-L138 datasheet is
+         * (2000 * prediv)/sqrt(pllm) OSCIN cycles. We approximate sqrt(pllm)
+         * as 4 and OSCIN cycle as 25 MHz.
+         */
+        if (prediv) {
+                locktime = ((2000 * prediv) / 100);
+                prediv = (prediv - 1) | PLLDIV_EN;
+        } else {
+                locktime = 20;
+        }
+        if (postdiv)
+                postdiv = (postdiv - 1) | PLLDIV_EN;
+        if (mult)
+                mult = mult - 1;
+
+        ctrl = __raw_readl(pll->base + PLLCTL);
+
+        /* Switch the PLL to bypass mode */
+        ctrl &= ~(PLLCTL_PLLENSRC | PLLCTL_PLLEN);
+        __raw_writel(ctrl, pll->base + PLLCTL);
+
+        /*
+         * Wait for 4 OSCIN/CLKIN cycles to ensure that the PLLC has switched
+         * to bypass mode. Delay of 1us ensures we are good for all > 4MHz
+         * OSCIN/CLKIN inputs. Typically the input is ~25MHz.
+         */
+        udelay(1);
+
+        /* Reset and enable PLL */
+        ctrl &= ~(PLLCTL_PLLRST | PLLCTL_PLLDIS);
+        __raw_writel(ctrl, pll->base + PLLCTL);
+
+        if (pll->flags & PLL_HAS_PREDIV)
+                __raw_writel(prediv, pll->base + PREDIV);
+
+        __raw_writel(mult, pll->base + PLLM);
+
+        if (pll->flags & PLL_HAS_POSTDIV)
+                __raw_writel(postdiv, pll->base + POSTDIV);
+
+        /*
+         * Wait for PLL to reset properly, OMAP-L138 datasheet says
+         * 'min' time = 125ns
+         */
+        udelay(1);
+
+        /* Bring PLL out of reset */
+        ctrl |= PLLCTL_PLLRST;
+        __raw_writel(ctrl, pll->base + PLLCTL);
+
+        udelay(locktime);
+
+        /* Remove PLL from bypass mode */
+        ctrl |= PLLCTL_PLLEN;
+        __raw_writel(ctrl, pll->base + PLLCTL);
+
+        return 0;
+}
+EXPORT_SYMBOL(davinci_set_pllrate);
+
 int __init davinci_clk_init(struct davinci_clk *clocks)
   {
         struct davinci_clk *c;
diff --git a/arch/arm/mach-davinci/clock.h b/arch/arm/mach-davinci/clock.h
index 202b9ff27b9d..a75d3f70b351 100644
--- a/arch/arm/mach-davinci/clock.h
+++ b/arch/arm/mach-davinci/clock.h
@@ -22,6 +22,10 @@
 /* PLL/Reset register offsets */
 #define PLLCTL          0x100
 #define PLLCTL_PLLEN    BIT(0)
+#define PLLCTL_PLLPWRDN BIT(1)
+#define PLLCTL_PLLRST   BIT(3)
+#define PLLCTL_PLLDIS   BIT(4)
+#define PLLCTL_PLLENSRC BIT(5)
 #define PLLCTL_CLKMODE  BIT(8)
 
 #define PLLM            0x110
@@ -74,6 +78,8 @@ struct clk {
         struct pll_data         *pll_data;
         u32                     div_reg;
         unsigned long (*recalc) (struct clk *);
+        int (*set_rate) (struct clk *clk, unsigned long rate);
+        int (*round_rate) (struct clk *clk, unsigned long rate);
 };
 
 /* Clock flags */
@@ -97,6 +103,8 @@ struct davinci_clk {
         }
 
 int davinci_clk_init(struct davinci_clk *clocks);
+int davinci_set_pllrate(struct pll_data *pll, unsigned int prediv,
+                                unsigned int mult, unsigned int postdiv);
 
 extern struct platform_device davinci_wdt_device;