The AT91 PLL rate configuration is done by configuring a multiplier/divider
pair.
The previous calculation was over-complicated (and apparently buggy).
Simplify the implementation and add some comments to explain what is done
here.
Signed-off-by: Boris BREZILLON <boris.brezil...@free-electrons.com>
Reported-by: Gaël PORTAY <gael.por...@gmail.com>
---
drivers/clk/at91/clk-pll.c | 147 ++++++++++++++++++++++++---------------------
1 file changed, 77 insertions(+), 70 deletions(-)
diff --git a/drivers/clk/at91/clk-pll.c b/drivers/clk/at91/clk-pll.c
index 7b453b9..a1adcf1 100644
--- a/drivers/clk/at91/clk-pll.c
+++ b/drivers/clk/at91/clk-pll.c
@@ -15,6 +15,7 @@
#include <linux/of_address.h>
#include <linux/of_irq.h>
#include <linux/io.h>
+#include <linux/kernel.h>
#include <linux/wait.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
@@ -29,6 +30,9 @@
#define PLL_DIV(reg) ((reg) & PLL_DIV_MASK)
#define PLL_MUL(reg, layout) (((reg) >> (layout)->mul_shift) & \
(layout)->mul_mask)
+#define PLL_MUL_MIN 2
+#define PLL_MUL_MASK(layout) ((layout)->mul_mask)
+#define PLL_MUL_MAX(layout) (PLL_MUL_MASK(layout) + 1)
#define PLL_ICPR_SHIFT(id) ((id) * 16)
#define PLL_ICPR_MASK(id) (0xffff << PLL_ICPR_SHIFT(id))
#define PLL_MAX_COUNT 0x3f
@@ -163,99 +167,102 @@ static long clk_pll_get_best_div_mul(struct clk_pll
*pll, unsigned long rate,
unsigned long parent_rate,
u32 *div, u32 *mul,
u32 *index) {
- unsigned long maxrate;
- unsigned long minrate;
- unsigned long divrate;
- unsigned long bestdiv = 1;
- unsigned long bestmul;
- unsigned long tmpdiv;
- unsigned long roundup;
- unsigned long rounddown;
- unsigned long remainder;
- unsigned long bestremainder;
- unsigned long maxmul;
- unsigned long maxdiv;
- unsigned long mindiv;
- int i = 0;
const struct clk_pll_layout *layout = pll->layout;
const struct clk_pll_characteristics *characteristics =
pll->characteristics;
+ unsigned long bestremainder = ULONG_MAX;
+ unsigned long maxdiv, mindiv, tmpdiv;
+ long bestrate = -ERANGE;
+ unsigned long bestdiv;
+ unsigned long bestmul;
+ int i = 0;
- /* Minimum divider = 1 */
- /* Maximum multiplier = max_mul */
- maxmul = layout->mul_mask + 1;
- maxrate = (parent_rate * maxmul) / 1;
-
- /* Maximum divider = max_div */
- /* Minimum multiplier = 2 */
- maxdiv = PLL_DIV_MAX;
- minrate = (parent_rate * 2) / maxdiv;
-
+ /* Check if parent_rate is a valid input rate */
if (parent_rate < characteristics->input.min ||
- parent_rate < characteristics->input.max)
- return -ERANGE;
-
- if (parent_rate < minrate || parent_rate > maxrate)
+ parent_rate > characteristics->input.max)
return -ERANGE;
- for (i = 0; i < characteristics->num_output; i++) {
- if (parent_rate >= characteristics->output[i].min &&
- parent_rate <= characteristics->output[i].max)
- break;
- }
-
- if (i >= characteristics->num_output)
- return -ERANGE;
-
- bestmul = rate / parent_rate;
- rounddown = parent_rate % rate;
- roundup = rate - rounddown;
- bestremainder = roundup < rounddown ? roundup : rounddown;
-
- if (!bestremainder) {
- if (div)
- *div = bestdiv;
- if (mul)
- *mul = bestmul;
- if (index)
- *index = i;
- return rate;
- }
-
- maxdiv = 255 / (bestmul + 1);
- if (parent_rate / maxdiv < characteristics->input.min)
- maxdiv = parent_rate / characteristics->input.min;
- mindiv = parent_rate / characteristics->input.max;
- if (parent_rate % characteristics->input.max)
- mindiv++;
-
- for (tmpdiv = mindiv; tmpdiv < maxdiv; tmpdiv++) {
- divrate = parent_rate / tmpdiv;
-
- rounddown = rate % divrate;
- roundup = divrate - rounddown;
- remainder = roundup < rounddown ? roundup : rounddown;
-
+ /*
+ * Calculate minimum divider based on the minimum multiplier, the
+ * parent_rate and the requested rate.
+ * Should always be 2 according to the input and output characteristics
+ * of the PLL blocks.
+ */
+ mindiv = (parent_rate * PLL_MUL_MIN) / rate;
+ if (!mindiv)
+ mindiv = 1;
+
+ /*
+ * Calculate the maximum divider which is limited by PLL register
+ * layout (limited by the MUL or DIV field size).
+ */
+ maxdiv = DIV_ROUND_UP(parent_rate * PLL_MUL_MAX(layout), rate);
+ if (maxdiv > PLL_DIV_MAX)
+ maxdiv = PLL_DIV_MAX;
+
+ /*
+ * Iterate over the acceptable divider values to find the best
+ * divider/multiplier pair (the one that generates the closest
+ * rate to the requested one).
+ */
+ for (tmpdiv = mindiv; tmpdiv <= maxdiv; tmpdiv++) {
+ unsigned long remainder;
+ unsigned long tmprate;
+ unsigned long tmpmul;
+
+ /*
+ * Calculate the multiplier associated with the current
+ * divider that provide the closest rate to the requested one.
+ */
+ tmpmul = DIV_ROUND_CLOSEST(rate, parent_rate / tmpdiv);
+ tmprate = (parent_rate / tmpdiv) * tmpmul;
+ if (tmprate > rate)
+ remainder = tmprate - rate;
+ else
+ remainder = rate - tmprate;
+
+ /*
+ * Compare the remainder with the best remainder found until
+ * now and elect a new best multiplier/divider pair if the
+ * current remainder is smaller than the best one.
+ */
if (remainder < bestremainder) {
bestremainder = remainder;
- bestmul = rate / divrate;
bestdiv = tmpdiv;
+ bestmul = tmpmul;
+ bestrate = tmprate;
}
+ /*
+ * We've found a perfect match!
+ * Stop searching now and use this multiplier/divider pair.
+ */
if (!remainder)
break;
}
- rate = (parent_rate / bestdiv) * bestmul;
+ /* We haven't found any multiplier/divider pair => return -ERANGE */
+ if (bestrate < 0)
+ return bestrate;
+
+ /* Check if bestrate is a valid output rate */
+ for (i = 0; i < characteristics->num_output; i++) {
+ if (bestrate >= characteristics->output[i].min &&
+ bestrate <= characteristics->output[i].max)
+ break;
+ }
+
+ if (i >= characteristics->num_output)
+ return -ERANGE;
if (div)
*div = bestdiv;
if (mul)
- *mul = bestmul;
+ *mul = bestmul - 1;
if (index)
*index = i;
- return rate;
+ return bestrate;
}
static long clk_pll_round_rate(struct clk_hw *hw, unsigned long rate,
--
1.9.1
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