[PATCH] clk: imx: add fractional-N pll support to pllv4

[Anson Huang]

The pllv4 supports fractional-N function, the formula is:

PLL output freq = input * (mult + num/denom),

This patch adds fractional-N function support, including
clock round rate, calculate rate and set rate, with this
patch, the clock rate of APLL in clock tree is more accurate
than before:

Without fraction:
apll_pre_sel                      1        1        1    24000000          0     0  50000
   apll_pre_div                   1        1        2    24000000          0     0  50000
      apll                        1        1        2   528000000          0     0  50000
         apll_pfd3                0        0        0   792000000          0     0  50000
         apll_pfd2                0        0        0   339428571          0     0  50000
         apll_pfd1                0        0        0   352000000          0     0  50000
            usdhc0                0        0        0   352000000          0     0  50000
         apll_pfd0                1        1        1   352000000          0     0  50000

With fraction:
apll_pre_sel                      1        1        1    24000000          0     0  50000
   apll_pre_div                   1        1        2    24000000          0     0  50000
      apll                        1        1        2   529200000          0     0  50000
         apll_pfd3                0        0        0   793800000          0     0  50000
         apll_pfd2                0        0        0   340200000          0     0  50000
         apll_pfd1                0        0        0   352800000          0     0  50000
            usdhc0                0        0        0   352800000          0     0  50000
         apll_pfd0                1        1        1   352800000          0     0  50000

Signed-off-by: Anson Huang <Anson.Huang@xxxxxxx>
---
 drivers/clk/imx/clk-pllv4.c | 68 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 60 insertions(+), 8 deletions(-)

diff --git a/drivers/clk/imx/clk-pllv4.c b/drivers/clk/imx/clk-pllv4.c
index d38bc9f..4ced5ca 100644
--- a/drivers/clk/imx/clk-pllv4.c
+++ b/drivers/clk/imx/clk-pllv4.c
@@ -64,13 +64,18 @@ static unsigned long clk_pllv4_recalc_rate(struct clk_hw *hw,
 					   unsigned long parent_rate)
 {
 	struct clk_pllv4 *pll = to_clk_pllv4(hw);
-	u32 div;
+	u32 mult = readl_relaxed(pll->base + PLL_CFG_OFFSET);
+	u32 mfn = readl_relaxed(pll->base + PLL_NUM_OFFSET);
+	u32 mfd = readl_relaxed(pll->base + PLL_DENOM_OFFSET);
+	u64 temp64 = parent_rate;
 
-	div = readl_relaxed(pll->base + PLL_CFG_OFFSET);
-	div &= BM_PLL_MULT;
-	div >>= BP_PLL_MULT;
+	mult &= BM_PLL_MULT;
+	mult >>= BP_PLL_MULT;
 
-	return parent_rate * div;
+	temp64 *= mfn;
+	do_div(temp64, mfd);
+
+	return (parent_rate * mult) + (u32)temp64;
 }
 
 static long clk_pllv4_round_rate(struct clk_hw *hw, unsigned long rate,
@@ -78,14 +83,47 @@ static long clk_pllv4_round_rate(struct clk_hw *hw, unsigned long rate,
 {
 	unsigned long parent_rate = *prate;
 	unsigned long round_rate, i;
+	bool found = false;
+	u32 mfn, mfd = 1000000;
+	u32 max_mfd = 0x3FFFFFFF;
+	u64 temp64;
 
 	for (i = 0; i < ARRAY_SIZE(pllv4_mult_table); i++) {
 		round_rate = parent_rate * pllv4_mult_table[i];
-		if (rate >= round_rate)
-			return round_rate;
+		if (rate >= round_rate) {
+			found = true;
+			break;
+		}
+	}
+
+	if (!found) {
+		pr_warn("%s: unable to round rate %lu, parent rate %lu\n",
+			clk_hw_get_name(hw), rate, parent_rate);
+		return 0;
 	}
 
-	return round_rate;
+	if (parent_rate <= max_mfd)
+		mfd = parent_rate;
+
+	temp64 = (u64)(rate - round_rate);
+	temp64 *= mfd;
+	do_div(temp64, parent_rate);
+	mfn = temp64;
+
+	/*
+	 * NOTE: The value of numerator must always be configured to be
+	 * less than the value of the denominator. If we can't get a proper
+	 * pair of mfn/mfd, we simply return the round_rate without using
+	 * the frac part.
+	 */
+	if (mfn >= mfd)
+		return round_rate;
+
+	temp64 = (u64)parent_rate;
+	temp64 *= mfn;
+	do_div(temp64, mfd);
+
+	return round_rate + (u32)temp64;
 }
 
 static bool clk_pllv4_is_valid_mult(unsigned int mult)
@@ -106,17 +144,31 @@ static int clk_pllv4_set_rate(struct clk_hw *hw, unsigned long rate,
 {
 	struct clk_pllv4 *pll = to_clk_pllv4(hw);
 	u32 val, mult;
+	u32 mfn, mfd = 1000000;
+	u32 max_mfd = 0x3FFFFFFF;
+	u64 temp64;
 
 	mult = rate / parent_rate;
 
 	if (!clk_pllv4_is_valid_mult(mult))
 		return -EINVAL;
 
+	if (parent_rate <= max_mfd)
+		mfd = parent_rate;
+
+	temp64 = (u64)(rate - mult * parent_rate);
+	temp64 *= mfd;
+	do_div(temp64, parent_rate);
+	mfn = temp64;
+
 	val = readl_relaxed(pll->base + PLL_CFG_OFFSET);
 	val &= ~BM_PLL_MULT;
 	val |= mult << BP_PLL_MULT;
 	writel_relaxed(val, pll->base + PLL_CFG_OFFSET);
 
+	writel_relaxed(mfn, pll->base + PLL_NUM_OFFSET);
+	writel_relaxed(mfd, pll->base + PLL_DENOM_OFFSET);
+
 	return 0;
 }
 
-- 
2.7.4