linux-kernel - Re: [PATCH v3 1/4] clk: bcm2835: add a round up ability to the clock divisor

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Message-ID: <878u55d8zn.fsf@eliezer.anholt.net>
Date:	Mon, 07 Dec 2015 17:28:28 -0800
From:	Eric Anholt <eric@...olt.net>
To:	Remi Pommarel <repk@...plefau.lt>,
	Stephen Warren <swarren@...dotorg.org>,
	Lee Jones <lee@...nel.org>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Rob Herring <robh+dt@...nel.org>
Cc:	linux-rpi-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
	linux-kernel@...r.kernel.org, Remi Pommarel <repk@...plefau.lt>
Subject: Re: [PATCH v3 1/4] clk: bcm2835: add a round up ability to the clock divisor

Remi Pommarel <repk@...plefau.lt> writes:

> Make bcm2835_clock_choose_div to optionally round up the chosen MASH divisor
> so that the resulting average rate will not be higher than the requested one.
>
> Signed-off-by: Remi Pommarel <repk@...plefau.lt>
> ---
>  drivers/clk/bcm/clk-bcm2835.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
> index 39bf582..9e881ee 100644
> --- a/drivers/clk/bcm/clk-bcm2835.c
> +++ b/drivers/clk/bcm/clk-bcm2835.c
> @@ -1148,22 +1148,24 @@ static int bcm2835_clock_is_on(struct clk_hw *hw)
>  
>  static u32 bcm2835_clock_choose_div(struct clk_hw *hw,
>  				    unsigned long rate,
> -				    unsigned long parent_rate)
> +				    unsigned long parent_rate,
> +				    bool round_up)
>  {
>  	struct bcm2835_clock *clock = bcm2835_clock_from_hw(hw);
>  	const struct bcm2835_clock_data *data = clock->data;
> -	u32 unused_frac_mask = GENMASK(CM_DIV_FRAC_BITS - data->frac_bits, 0);
> +	u32 unused_frac_mask =
> +		GENMASK(CM_DIV_FRAC_BITS - data->frac_bits, 0) >> 1;
>  	u64 temp = (u64)parent_rate << CM_DIV_FRAC_BITS;
> +	u64 rem;
>  	u32 div;
>  
> -	do_div(temp, rate);
> +	rem = do_div(temp, rate);
>  	div = temp;
>  
> -	/* Round and mask off the unused bits */
> -	if (unused_frac_mask != 0) {
> -		div += unused_frac_mask >> 1;
> -		div &= ~unused_frac_mask;
> -	}
> +	/* Round up and mask off the unused bits */
> +	if (round_up && ((div & unused_frac_mask) != 0 || rem != 0))
> +		div += unused_frac_mask + 1;
> +	div &= ~unused_frac_mask;
>  
>  	/* Clamp to the limits. */
>  	div = max(div, unused_frac_mask + 1);
> @@ -1202,7 +1204,7 @@ static long bcm2835_clock_round_rate(struct clk_hw *hw,
>  				     unsigned long *parent_rate)
>  {
>  	struct bcm2835_clock *clock = bcm2835_clock_from_hw(hw);
> -	u32 div = bcm2835_clock_choose_div(hw, rate, *parent_rate);
> +	u32 div = bcm2835_clock_choose_div(hw, rate, *parent_rate, false);
>  
>  	return bcm2835_clock_rate_from_divisor(clock, *parent_rate, div);
>  }
> @@ -1271,7 +1273,7 @@ static int bcm2835_clock_set_rate(struct clk_hw *hw,
>  	struct bcm2835_clock *clock = bcm2835_clock_from_hw(hw);
>  	struct bcm2835_cprman *cprman = clock->cprman;
>  	const struct bcm2835_clock_data *data = clock->data;
> -	u32 div = bcm2835_clock_choose_div(hw, rate, parent_rate);
> +	u32 div = bcm2835_clock_choose_div(hw, rate, parent_rate, false);

I think you meant ", true" on one of these.  With that fixed,

Reviewed-by: Eric Anholt <eric@...olt.net>

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