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Commit ec52e462 authored by Elaine Zhang's avatar Elaine Zhang Committed by Heiko Stuebner
Browse files

clk: fractional-divider: allow overriding of approximation 



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: default avatarElaine Zhang <zhangqing@rock-chips.com>
Acked-by: default avatarStephen Boyd <sboyd@codeaurora.org>
Signed-off-by: default avatarHeiko Stuebner <heiko@sntech.de>
parent 33461405

drivers/clk/clk-fractional-divider.c

+20 −8
Original line number Diff line number Diff line
@@ -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);

include/linux/clk-provider.h

+3 −0
Original line number Diff line number Diff line
@@ -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;

};