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clk: fractional-divider: add handle to frac numerator is not to be greater than 4

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We know that under the condition of even frequency division,
if the numeratoris greater than 4, the duty cycle may not be
equal to 50%.

In the case, weneed to keep the original numerator(<4) and
denominator.

Change-Id: I8cd08199df4e3d27d5697ce80370224a6f267e26
Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>
This commit is contained in:
Xing Zheng
2019-12-27 21:31:23 +08:00
committed by Elaine Zhang
parent f8de58c732
commit d00bfccedf
1 changed files with 10 additions and 1 deletions
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11
drivers/clk/clk-fractional-divider.c
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@@ -112,9 +112,18 @@ static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate,
* which will lead to a large deviation in the result.
* Therefore, it is required that the numerator must
* be greater than 4.
*
* Note that there are some exceptions here:
* If there is an even frac div, we need to keep the original
* numerator(<4) and denominator. Otherwise, it may cause the
* issue that the duty ratio is not 50%.
*/
if (m < 4 && m != 0) {
val = DIV_ROUND_UP(4, m);
if (n % 2 == 0)
val = 1;
else
val = DIV_ROUND_UP(4, m);
n *= val;
m *= val;
if (n > fd->nmask) {