From da321133b53caf7889ed3ca1dabe4cc368db2604 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Uwe=20Kleine-K=C3=B6nig?= Date: Sat, 21 Feb 2015 11:40:23 +0100 Subject: [PATCH] clk: divider: fix calculation of maximal parent rate for a given divider MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The rate provided at the output of a clk-divider is calculated as: DIV_ROUND_UP(parent_rate, div) since commit b11d282dbea2 (clk: divider: fix rate calculation for fractional rates). So to yield a rate not bigger than r parent_rate must be <= r * div. The effect of choosing a parent rate that is too big as was done before this patch results in wrongly ruling out good dividers. Note that this is not a complete fix as __clk_round_rate might return a value >= its 2nd parameter. Also for dividers with CLK_DIVIDER_ROUND_CLOSEST set the calculation is not accurate. But this fixes the test case by Sascha Hauer that uses a chain of three dividers under a fixed clock. Fixes: b11d282dbea2 (clk: divider: fix rate calculation for fractional rates) Suggested-by: Sascha Hauer Signed-off-by: Uwe Kleine-König Acked-by: Sascha Hauer Signed-off-by: Michael Turquette --- drivers/clk/clk-divider.c | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-) diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c index eff8a862eb08..a1a029092c8d 100644 --- a/drivers/clk/clk-divider.c +++ b/drivers/clk/clk-divider.c @@ -144,12 +144,6 @@ static unsigned long clk_divider_recalc_rate(struct clk_hw *hw, divider->flags); } -/* - * The reverse of DIV_ROUND_UP: The maximum number which - * divided by m is r - */ -#define MULT_ROUND_UP(r, m) ((r) * (m) + (m) - 1) - static bool _is_valid_table_div(const struct clk_div_table *table, unsigned int div) { @@ -313,7 +307,7 @@ static int clk_divider_bestdiv(struct clk_hw *hw, unsigned long rate, return i; } parent_rate = __clk_round_rate(__clk_get_parent(hw->clk), - MULT_ROUND_UP(rate, i)); + rate * i); now = DIV_ROUND_UP(parent_rate, i); if (_is_best_div(rate, now, best, flags)) { bestdiv = i; -- 2.20.1