[V2,1/4] clk: imx: pll14xx: avoid glitch when set rate

Commit Message

Peng Fan Aug. 26, 2019, 9:42 a.m. UTC

From: Peng Fan <[e-mail]>

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: 8646d4dcc7fb ("clk: imx: Add PLLs driver for imx8mm soc")
Reviewed-by: Leonard Crestez <[e-mail]>
Signed-off-by: Peng Fan <[e-mail]>
---

V2:
  Avoid glitch when prepare
  update commit log

 drivers/clk/imx/clk-pll14xx.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

Comments

Stephen Boyd Sept. 6, 2019, 5:21 p.m. UTC | #1

Quoting Peng Fan (2019-08-26 02:42:14)
> From: Peng Fan <[e-mail]>
> 
> 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: 8646d4dcc7fb ("clk: imx: Add PLLs driver for imx8mm soc")
> Reviewed-by: Leonard Crestez <[e-mail]>
> Signed-off-by: Peng Fan <[e-mail]>
> ---

Please make cover letters for multi-patch series.

Peng Fan Sept. 9, 2019, 3:40 a.m. UTC | #2

Hi Stephen,

> Subject: Re: [PATCH V2 1/4] clk: imx: pll14xx: avoid glitch when set rate
> 
> Quoting Peng Fan (2019-08-26 02:42:14)
> > From: Peng Fan <[e-mail]>
> >
> > 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: 8646d4dcc7fb ("clk: imx: Add PLLs driver for imx8mm soc")
> > Reviewed-by: Leonard Crestez <[e-mail]>
> > Signed-off-by: Peng Fan <[e-mail]>
> > ---
> 
> Please make cover letters for multi-patch series.

Just sent out v3 to include cover-letter, no other changes.

Thanks,
Peng.

Patch

diff --git a/drivers/clk/imx/clk-pll14xx.c b/drivers/clk/imx/clk-pll14xx.c
index b7213023b238..656f48b002dd 100644
--- a/drivers/clk/imx/clk-pll14xx.c
+++ b/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)