lkml.org 
[lkml]   [2015]   [Feb]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 1/3] clk: divider: fix calculation of maximal parent rate for a given divider
Date
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 <s.hauer@pengutronix.de>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
---
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 531d5a48e69f..fbd9e8270791 100644
--- a/drivers/clk/clk-divider.c
+++ b/drivers/clk/clk-divider.c
@@ -129,12 +129,6 @@ static unsigned long clk_divider_recalc_rate(struct clk_hw *hw,
return DIV_ROUND_UP(parent_rate, div);
}

-/*
- * 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)
{
@@ -300,7 +294,7 @@ 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(divider, rate, now, best)) {
bestdiv = i;
--
2.1.4


\
 
 \ /
  Last update: 2015-02-21 12:01    [W:0.347 / U:0.280 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site