Messages in this thread | | | From | Eric Miao <> | Date | Wed, 15 Jun 2011 16:34:31 +0800 | Subject | Re: [PATCH] i2c: imx: choose the better clock divider |
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Sorry forgot to include Ben.
Ben, any ideas?
On Tue, Jun 14, 2011 at 3:17 PM, Eric Miao <eric.miao@linaro.org> wrote: > 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@linaro.org> > Signed-off-by: Eric Miao <eric.miao@linaro.org> > --- > 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 > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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