The original algorithm doesn't perform very well in some cases, e.g.
When the source clock of the I2C controller is 66MHz, and the
requested rate is 100KHz, it gives a divider of 768 instead of
the better 640.
Choose a better clock divider so the final clock rate is closer to
the requested one by comparing the rate distances calculated by
two adjacent dividers.
Cc: Richard Zhao <richard.zhao@xxxxxxxxxx>
Signed-off-by: Eric Miao <eric.miao@xxxxxxxxxx>
---
drivers/i2c/busses/i2c-imx.c | 46 ++++++++++++++++++++++++++++-------------
1 files changed, 31 insertions(+), 15 deletions(-)
diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index 4c2a62b..cd640ff 100644
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -112,6 +112,8 @@ static u16 __initdata i2c_clk_div[50][2] = {
{ 3072, 0x1E }, { 3840, 0x1F }
};
+#define I2C_CLK_DIV_NUM ARRAY_SIZE(i2c_clk_div)
+
struct imx_i2c_struct {
struct i2c_adapter adapter;
struct resource *res;
@@ -240,22 +242,37 @@ static void i2c_imx_stop(struct imx_i2c_struct *i2c_imx)
clk_disable(i2c_imx->clk);
}
-static void __init i2c_imx_set_clk(struct imx_i2c_struct *i2c_imx,
- unsigned int rate)
+/* find the index into i2c_clk_div[] array, compare with the two
+ * dividers found, return the one with smaller error
+ */
+static int find_div(unsigned long i2c_clk_rate, unsigned long rate)
{
- unsigned int i2c_clk_rate;
- unsigned int div;
+ unsigned long div, delta_l, delta_h;
int i;
- /* Divider value calculation */
- i2c_clk_rate = clk_get_rate(i2c_imx->clk);
div = (i2c_clk_rate + rate - 1) / rate;
+
if (div < i2c_clk_div[0][0])
- i = 0;
- else if (div > i2c_clk_div[ARRAY_SIZE(i2c_clk_div) - 1][0])
- i = ARRAY_SIZE(i2c_clk_div) - 1;
- else
- for (i = 0; i2c_clk_div[i][0] < div; i++);
+ return 0;
+
+ if (div > i2c_clk_div[I2C_CLK_DIV_NUM - 1][0])
+ return I2C_CLK_DIV_NUM;
+
+ for (i = 0; i < I2C_CLK_DIV_NUM; i++)
+ if (i2c_clk_div[i][0] > div)
+ break;
+
+ delta_h = (i2c_clk_rate / i2c_clk_div[i - 1][0]) - rate;
+ delta_l = rate - (i2c_clk_rate / i2c_clk_div[i][0]);
+
+ return (delta_l < delta_h) ? i : i - 1;
+}
+
+static void __init i2c_imx_set_clk(struct imx_i2c_struct *i2c_imx,
+ unsigned int rate)
+{
+ unsigned long i2c_clk_rate = clk_get_rate(i2c_imx->clk);
+ int i = find_div(i2c_clk_rate, rate);
/* Store divider value */
i2c_imx->ifdr = i2c_clk_div[i][1];
@@ -271,10 +288,9 @@ static void __init i2c_imx_set_clk(struct imx_i2c_struct *i2c_imx,
/* dev_dbg() can't be used, because adapter is not yet registered */
#ifdef CONFIG_I2C_DEBUG_BUS
- printk(KERN_DEBUG "I2C: <%s> I2C_CLK=%d, REQ DIV=%d\n",
- __func__, i2c_clk_rate, div);
- printk(KERN_DEBUG "I2C: <%s> IFDR[IC]=0x%x, REAL DIV=%d\n",
- __func__, i2c_clk_div[i][1], i2c_clk_div[i][0]);
+ pr_debug("<%s> I2C_CLK=%ld, REQ RATE=%d, DIV=%d, IFDR[IC]=0x%x\n",
+ __func__, i2c_clk_rate, rate,
+ i2c_clk_div[i][0], i2c_clk_div[i][1]);
#endif
}
--
1.7.4.1
--
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