clk: imx: pll14xx: avoid glitch when set rate

According to PLL1443XA and PLL1416X spec,
"When BYPASS is 0 and RESETB is changed from 0 to 1, FOUT starts to
output unstable clock until lock time passes. PLL1416X/PLL1443XA may
generate a glitch at FOUT."

So set BYPASS when RESETB is changed from 0 to 1 to avoid glitch.
In the end of set rate, BYPASS will be cleared.

When prepare clock, also need to take care to avoid glitch. So
we also follow Spec to set BYPASS before RESETB changed from 0 to 1.
And add a check if the RESETB is already 0, directly return 0;

Fixes: 8646d4dcc7 ("clk: imx: Add PLLs driver for imx8mm soc")
Reviewed-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lkml.kernel.org/r/1568043491-20680-2-git-send-email-peng.fan@nxp.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/imx/clk-pll14xx.c

@@ -191,6 +191,10 @@ static int clk_pll1416x_set_rate(struct clk_hw *hw, unsigned long drate,
 	tmp &= ~RST_MASK;
 	writel_relaxed(tmp, pll->base);
 
+	/* Enable BYPASS */
+	tmp |= BYPASS_MASK;
+	writel(tmp, pll->base);
+
 	div_val = (rate->mdiv << MDIV_SHIFT) | (rate->pdiv << PDIV_SHIFT) |
 		(rate->sdiv << SDIV_SHIFT);
 	writel_relaxed(div_val, pll->base + 0x4);
@@ -250,6 +254,10 @@ static int clk_pll1443x_set_rate(struct clk_hw *hw, unsigned long drate,
 	tmp &= ~RST_MASK;
 	writel_relaxed(tmp, pll->base);
 
+	/* Enable BYPASS */
+	tmp |= BYPASS_MASK;
+	writel_relaxed(tmp, pll->base);
+
 	div_val = (rate->mdiv << MDIV_SHIFT) | (rate->pdiv << PDIV_SHIFT) |
 		(rate->sdiv << SDIV_SHIFT);
 	writel_relaxed(div_val, pll->base + 0x4);
@@ -283,16 +291,28 @@ static int clk_pll14xx_prepare(struct clk_hw *hw)
 {
 	struct clk_pll14xx *pll = to_clk_pll14xx(hw);
 	u32 val;
+	int ret;
 
 	/*
 	 * RESETB = 1 from 0, PLL starts its normal
 	 * operation after lock time
 	 */
 	val = readl_relaxed(pll->base + GNRL_CTL);
+	if (val & RST_MASK)
+		return 0;
+	val |= BYPASS_MASK;
+	writel_relaxed(val, pll->base + GNRL_CTL);
 	val |= RST_MASK;
 	writel_relaxed(val, pll->base + GNRL_CTL);
 
-	return clk_pll14xx_wait_lock(pll);
+	ret = clk_pll14xx_wait_lock(pll);
+	if (ret)
+		return ret;
+
+	val &= ~BYPASS_MASK;
+	writel_relaxed(val, pll->base + GNRL_CTL);
+
+	return 0;
 }
 
 static int clk_pll14xx_is_prepared(struct clk_hw *hw)