Re: [PATCH 1/2] clk: fractional-divider: allow overriding of approximation

[Elaine Zhang <zhangqing@rock-chips.com>]

hi,heiko:

This a good solution.And I tested it on RK SOCs.It's work well.

On 08/02/2017 12:21 AM, Heiko Stuebner wrote:
> From: Elaine Zhang <zhangqing@rock-chips.com>
>
> Fractional dividers may have special requirements concerning numerator
> and denominator selection that differ from just getting the best
> approximation.
>
> For example on Rockchip socs the denominator must be at least 20 times
> larger than the numerator to generate precise clock frequencies.
>
> Therefore add the ability to provide custom approximation functions.
>
> Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>
> ---
>   drivers/clk/clk-fractional-divider.c | 28 ++++++++++++++++++++--------
>   include/linux/clk-provider.h         |  3 +++
>   2 files changed, 23 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c
> index aab904618eb6..fdf625fb10fa 100644
> --- a/drivers/clk/clk-fractional-divider.c
> +++ b/drivers/clk/clk-fractional-divider.c
> @@ -49,16 +49,12 @@ static unsigned long clk_fd_recalc_rate(struct clk_hw *hw,
>   	return ret;
>   }
>
> -static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,
> -			      unsigned long *parent_rate)
> +static void clk_fd_general_approximation(struct clk_hw *hw, unsigned long rate,
> +					 unsigned long *parent_rate,
> +					 unsigned long *m, unsigned long *n)
>   {
>   	struct clk_fractional_divider *fd = to_clk_fd(hw);
>   	unsigned long scale;
> -	unsigned long m, n;
> -	u64 ret;
> -
> -	if (!rate || rate >= *parent_rate)
> -		return *parent_rate;
>
>   	/*
>   	 * Get rate closer to *parent_rate to guarantee there is no overflow
> @@ -71,7 +67,23 @@ static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,
>
>   	rational_best_approximation(rate, *parent_rate,
>   			GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
> -			&m, &n);
> +			m, n);
> +}
> +
> +static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,
> +			      unsigned long *parent_rate)
> +{
> +	struct clk_fractional_divider *fd = to_clk_fd(hw);
> +	unsigned long m, n;
> +	u64 ret;
> +
> +	if (!rate || rate >= *parent_rate)
> +		return *parent_rate;
> +
> +	if (fd->approximation)
> +		fd->approximation(hw, rate, parent_rate, &m, &n);
> +	else
> +		clk_fd_general_approximation(hw, rate, parent_rate, &m, &n);
>
>   	ret = (u64)*parent_rate * m;
>   	do_div(ret, n);
> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> index c59c62571e4f..1fc113fbf955 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -565,6 +565,9 @@ struct clk_fractional_divider {
>   	u8		nwidth;
>   	u32		nmask;
>   	u8		flags;
> +	void		(*approximation)(struct clk_hw *hw,
> +				unsigned long rate, unsigned long *parent_rate,
> +				unsigned long *m, unsigned long *n);
>   	spinlock_t	*lock;
>   };
>
>
Tested-by: Elaine Zhang <zhangqing@rock-chips.com>