This is a note to let you know that I've just added the patch titled
clk: divider: fix calculation of maximal parent rate for a given divider
to the 3.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
clk-divider-fix-calculation-of-maximal-parent-rate-for-a-given-divider.patch
and it can be found in the queue-3.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From da321133b53caf7889ed3ca1dabe4cc368db2604 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <u.kleine-koenig@xxxxxxxxxxxxxx>
Date: Sat, 21 Feb 2015 11:40:23 +0100
Subject: clk: divider: fix calculation of maximal parent rate for a given divider
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From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <u.kleine-koenig@xxxxxxxxxxxxxx>
commit da321133b53caf7889ed3ca1dabe4cc368db2604 upstream.
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@xxxxxxxxxxxxxx>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Acked-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
Signed-off-by: Michael Turquette <mturquette@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/clk/clk-divider.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)
--- a/drivers/clk/clk-divider.c
+++ b/drivers/clk/clk-divider.c
@@ -129,12 +129,6 @@ static unsigned long clk_divider_recalc_
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)
{
@@ -304,7 +298,7 @@ static int clk_divider_bestdiv(struct cl
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;
Patches currently in stable-queue which might be from u.kleine-koenig@xxxxxxxxxxxxxx are
queue-3.19/clk-divider-fix-selection-of-divider-when-rounding-to-closest.patch
queue-3.19/clk-divider-fix-calculation-of-maximal-parent-rate-for-a-given-divider.patch
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