linux-kernel - Re: [PATCH 4/4] clk: si5351: Reset PLL after rate change

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Message-ID: <20150430184932.GB22000@deathray>
Date:	Thu, 30 Apr 2015 13:49:32 -0500
From:	Michael Welling <mwelling@...e.org>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Cc:	Mike Turquette <mturquette@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Jean-Francois Moine <moinejf@...e.fr>,
	Russell King <rmk+linux@....linux.org.uk>,
	devicetree@...r.kernel.org, linux-clk@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] clk: si5351: Reset PLL after rate change

On Thu, Apr 30, 2015 at 07:45:54PM +0200, Sebastian Hesselbarth wrote:
> When changing PLL rate significantly, PLLs have to be reset. Add a function
> to perform and check for successful PLL reset.
> 
> Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
> ---
> Cc: Mike Turquette <mturquette@...aro.org>
> Cc: Stephen Boyd <sboyd@...eaurora.org>
> Cc: Jean-Francois Moine <moinejf@...e.fr>
> Cc: Michael Welling <mwelling@...e.org>
> Cc: Russell King <rmk+linux@....linux.org.uk>
> Cc: devicetree@...r.kernel.org
> Cc: linux-clk@...r.kernel.org
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  drivers/clk/clk-si5351.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/drivers/clk/clk-si5351.c b/drivers/clk/clk-si5351.c
> index beeb57bbb04c..9b97c134e3c1 100644
> --- a/drivers/clk/clk-si5351.c
> +++ b/drivers/clk/clk-si5351.c
> @@ -366,6 +366,32 @@ static const struct clk_ops si5351_vxco_ops = {
>   *         = (MSNx_P1*MSNx_P3 + MSNx_P2 + 512*MSNx_P3)/(128*MSNx_P3)
>   *
>   */
> +static int si5351_pll_reset(struct si5351_hw_data *hwdata)
> +{
> +	unsigned long timeout;
> +	u8 mask = (hwdata->num == 0) ?
> +		SI5351_STATUS_LOL_A : SI5351_STATUS_LOL_B;
> +
> +	si5351_reg_write(hwdata->drvdata, SI5351_PLL_RESET,
> +			 (hwdata->num == 0) ? SI5351_PLL_RESET_A :
> +			 SI5351_PLL_RESET_B);
> +	timeout = jiffies + msecs_to_jiffies(100);
> +	do {
> +		if ((si5351_reg_read(hwdata->drvdata, SI5351_DEVICE_STATUS) &
> +		     mask) == 0)
> +			break;
> +		if (time_after(jiffies, timeout)) {
> +			dev_err(&hwdata->drvdata->client->dev,
> +				"timeout waiting for pll %d reset\n",
> +				hwdata->num);
> +			return -EBUSY;
> +		};
> +		udelay(250);
> +	} while (true);
> +
> +	return 0;
> +}
> +
>  static int _si5351_pll_reparent(struct si5351_driver_data *drvdata,
>  				int num, enum si5351_pll_src parent)
>  {
> @@ -519,6 +545,9 @@ static int si5351_pll_set_rate(struct clk_hw *hw, unsigned long rate,
>  		SI5351_CLK_INTEGER_MODE,
>  		(hwdata->params.p2 == 0) ? SI5351_CLK_INTEGER_MODE : 0);
>  
> +	/* reset pll after rate change */
> +	si5351_pll_reset(hwdata);
> +

What is the point of having a return code if it is not being used?

>  	dev_dbg(&hwdata->drvdata->client->dev,
>  		"%s - %s: p1 = %lu, p2 = %lu, p3 = %lu, parent_rate = %lu, rate = %lu\n",
>  		__func__, __clk_get_name(hwdata->hw.clk),
> -- 
> 2.1.0
> 
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