linux-kernel - Re: [PATCH 2/2] clk: si5351: Powerdown output when clock rate is 0.

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Message-ID: <5188D26B.6020000@gmail.com>
Date:	Tue, 07 May 2013 12:07:39 +0200
From:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
To:	Marek Belisko <marek.belisko@...il.com>
CC:	mturquette@...aro.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, daniel@...que.org,
	Marek Belisko <marek.belisko@...eamunlimited.com>
Subject: Re: [PATCH 2/2] clk: si5351: Powerdown output when clock rate is
 0.

On 05/07/2013 10:14 AM, Marek Belisko wrote:
> When rate is 0 powerdown clock output.
>
> Signed-off-by: Marek Belisko<marek.belisko@...eamunlimited.com>
> ---
>   drivers/clk/clk-si5351.c |   32 +++++++++++++++++++-------------
>   1 file changed, 19 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/clk/clk-si5351.c b/drivers/clk/clk-si5351.c
> index a8fc0f4..e254e76 100644
> --- a/drivers/clk/clk-si5351.c
> +++ b/drivers/clk/clk-si5351.c
> @@ -1042,20 +1042,22 @@ static int si5351_clkout_set_rate(struct clk_hw *hw, unsigned long rate,
>   	struct si5351_hw_data *hwdata =
>   		container_of(hw, struct si5351_hw_data, hw);
>   	unsigned long new_rate, new_err, err;
> -	unsigned char rdiv;
> +	unsigned char rdiv, pdn = 0;
>
>   	/* round to closed rdiv */
>   	rdiv = SI5351_OUTPUT_CLK_DIV_1;
> -	new_rate = parent_rate;
> -	err = abs(new_rate - rate);
> -	do {
> -		new_rate>>= 1;
> -		new_err = abs(new_rate - rate);
> -		if (new_err>  err || rdiv == SI5351_OUTPUT_CLK_DIV_128)
> -			break;
> -		rdiv++;
> -		err = new_err;
> -	} while (1);
> +	if (rate) {
> +		new_rate = parent_rate;

Marek,

initalizing pdn to SI5351_CLK_POWERDOWN and skip (with goto) to 
powerup/down call on zero rate will save us a level of indention here.

> +		err = abs(new_rate - rate);
> +		do {
> +			new_rate>>= 1;
> +			new_err = abs(new_rate - rate);
> +			if (new_err>  err || rdiv == SI5351_OUTPUT_CLK_DIV_128)
> +				break;
> +			rdiv++;
> +			err = new_err;
> +		} while (1);

of course, pdn should be set to 0 here.

> +	}
>
>   	/* write output divider */
>   	switch (hwdata->num) {
> @@ -1075,9 +1077,13 @@ static int si5351_clkout_set_rate(struct clk_hw *hw, unsigned long rate,
>   				rdiv<<  SI5351_OUTPUT_CLK_DIV_SHIFT);
>   	}
>
> -	/* powerup clkout */
> +	/* when rate is 0 powerdown output */
> +	if (rate == 0)
> +		pdn = SI5351_CLK_POWERDOWN;
> +
> +	/* powerup/down clkout */
>   	si5351_set_bits(hwdata->drvdata, SI5351_CLK0_CTRL + hwdata->num,
> -			SI5351_CLK_POWERDOWN, 0);
> +			SI5351_CLK_POWERDOWN, pdn);
>
>   	dev_dbg(&hwdata->drvdata->client->dev,
>   		"%s - %s: rdiv = %u, parent_rate = %lu, rate = %lu\n",

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