[PATCH 1/2] clk: sunxi: rewrite sun9i_a80_get_pll4_factors()

Hans de Goede
2015-01-24T11:56:31Z

The old implementation of sun9i_a80_get_pll4_factors() has several issues,
it checks against 256 / 512 in various places where it should use 255 / 511,
it does the wrong thing for low frequencies which are an even multiple of
6 MHz, e.g. if you ask it for 72 MHz it will result in 144 Mhz, and it does
not take into account that n must be at least 12. Moreover it is quite hard
to read / follow it.

This commit rewrites it to be correct in all cases, and makes it much easier
to follow the code / to read.

Cc: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
drivers/clk/sunxi/clk-sun9i-core.c | 57 +++++++++++++++++++-------------------
1 file changed, 29 insertions(+), 28 deletions(-)

diff --git a/drivers/clk/sunxi/clk-sun9i-core.c b/drivers/clk/sunxi/clk-sun9i-core.c
index 9b5e7a1..d8da77d 100644
--- a/drivers/clk/sunxi/clk-sun9i-core.c
+++ b/drivers/clk/sunxi/clk-sun9i-core.c
@@ -24,50 +24,51 @@

/**
- * sun9i_a80_get_pll4_factors() - calculates n, p, m factors for PLL1
+ * sun9i_a80_get_pll4_factors() - calculates n, p, m factors for PLL4
* PLL4 rate is calculated as follows
* rate = (parent_rate * n >> p) / (m + 1);
- * parent_rate is always 24Mhz
+ * parent_rate is always 24MHz
*
* p and m are named div1 and div2 in Allwinner's SDK
*/

static void sun9i_a80_get_pll4_factors(u32 *freq, u32 parent_rate,
- u8 *n, u8 *k, u8 *m, u8 *p)
+ u8 *n_ret, u8 *k, u8 *m_ret, u8 *p_ret)
{
- int div;
+ int n;
+ int m = 1;
+ int p = 1;

- /* Normalize value to a 6M multiple */
- div = DIV_ROUND_UP(*freq, 6000000);
+ /* Normalize value to a 6 MHz multiple (24 MHz / 4) */
+ n = DIV_ROUND_UP(*freq, 6000000);

- /* divs above 256 cannot be odd */
- if (div > 256)
- div = round_up(div, 2);
+ /* If n is too large switch to steps of 12 MHz */
+ if (n > 255) {
+ m = 0;
+ n = (n + 1) / 2;
+ }
+
+ /* If n is still too large switch to steps of 24 MHz */
+ if (n > 255) {
+ p = 0;
+ n = (n + 1) / 2;
+ }

- /* divs above 512 must be a multiple of 4 */
- if (div > 512)
- div = round_up(div, 4);
+ /* n must be between 12 and 255 */
+ if (n > 255)
+ n = 255;
+ else if (n < 12)
+ n = 12;

- *freq = 6000000 * div;
+ *freq = ((24000000 * n) >> p) / (m + 1);

/* we were called to round the frequency, we can now return */
- if (n == NULL)
+ if (n_ret == NULL)
return;

- /* p will be 1 for divs under 512 */
- if (div < 512)
- *p = 1;
- else
- *p = 0;
-
- /* m will be 1 if div is odd */
- if (div & 1)
- *m = 1;
- else
- *m = 0;
-
- /* calculate a suitable n based on m and p */
- *n = div / (*p + 1) / (*m + 1);
+ *n_ret = n;
+ *m_ret = m;
+ *p_ret = p;
}

static struct clk_factors_config sun9i_a80_pll4_config = {
--
2.1.0