From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Miao Subject: Re: [PATCH] i2c: imx: choose the better clock divider Date: Wed, 15 Jun 2011 16:34:31 +0800 Message-ID: References: <1308035825-22410-1-git-send-email-eric.miao@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <1308035825-22410-1-git-send-email-eric.miao-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Ben Dooks Cc: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Jean Delvare , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Eric Miao , Richard Zhao List-Id: linux-i2c@vger.kernel.org Sorry forgot to include Ben. Ben, any ideas? On Tue, Jun 14, 2011 at 3:17 PM, Eric Miao wrote= : > The original algorithm doesn't perform very well in some cases, e.g. > > =C2=A0When the source clock of the I2C controller is 66MHz, and the > =C2=A0requested rate is 100KHz, it gives a divider of 768 instead of > =C2=A0the 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 > Signed-off-by: Eric Miao > --- > =C2=A0drivers/i2c/busses/i2c-imx.c | =C2=A0 46 ++++++++++++++++++++++= ++++++------------- > =C2=A01 files changed, 31 insertions(+), 15 deletions(-) > > diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-im= x.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] =3D { > =C2=A0 =C2=A0 =C2=A0 =C2=A0{ 3072, 0x1E }, { 3840, 0x1F } > =C2=A0}; > > +#define I2C_CLK_DIV_NUM =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0ARRAY_SIZE(i2c_clk_div) > + > =C2=A0struct imx_i2c_struct { > =C2=A0 =C2=A0 =C2=A0 =C2=A0struct i2c_adapter =C2=A0 =C2=A0 =C2=A0ada= pter; > =C2=A0 =C2=A0 =C2=A0 =C2=A0struct resource =C2=A0 =C2=A0 =C2=A0 =C2=A0= *res; > @@ -240,22 +242,37 @@ static void i2c_imx_stop(struct imx_i2c_struct = *i2c_imx) > =C2=A0 =C2=A0 =C2=A0 =C2=A0clk_disable(i2c_imx->clk); > =C2=A0} > > -static void __init i2c_imx_set_clk(struct imx_i2c_struct *i2c_imx, > - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 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) > =C2=A0{ > - =C2=A0 =C2=A0 =C2=A0 unsigned int i2c_clk_rate; > - =C2=A0 =C2=A0 =C2=A0 unsigned int div; > + =C2=A0 =C2=A0 =C2=A0 unsigned long div, delta_l, delta_h; > =C2=A0 =C2=A0 =C2=A0 =C2=A0int i; > > - =C2=A0 =C2=A0 =C2=A0 /* Divider value calculation */ > - =C2=A0 =C2=A0 =C2=A0 i2c_clk_rate =3D clk_get_rate(i2c_imx->clk); > =C2=A0 =C2=A0 =C2=A0 =C2=A0div =3D (i2c_clk_rate + rate - 1) / rate; > + > =C2=A0 =C2=A0 =C2=A0 =C2=A0if (div < i2c_clk_div[0][0]) > - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 i =3D 0; > - =C2=A0 =C2=A0 =C2=A0 else if (div > i2c_clk_div[ARRAY_SIZE(i2c_clk_= div) - 1][0]) > - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 i =3D ARRAY_SIZE(i= 2c_clk_div) - 1; > - =C2=A0 =C2=A0 =C2=A0 else > - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 for (i =3D 0; i2c_= clk_div[i][0] < div; i++); > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 return 0; > + > + =C2=A0 =C2=A0 =C2=A0 if (div > i2c_clk_div[I2C_CLK_DIV_NUM - 1][0]) > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 return I2C_CLK_DIV= _NUM; > + > + =C2=A0 =C2=A0 =C2=A0 for (i =3D 0; i < I2C_CLK_DIV_NUM; i++) > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 if (i2c_clk_div[i]= [0] > div) > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0 break; > + > + =C2=A0 =C2=A0 =C2=A0 delta_h =3D (i2c_clk_rate / i2c_clk_div[i - 1]= [0]) - rate; > + =C2=A0 =C2=A0 =C2=A0 delta_l =3D rate - (i2c_clk_rate / i2c_clk_div= [i][0]); > + > + =C2=A0 =C2=A0 =C2=A0 return (delta_l < delta_h) ? i : i - 1; > +} > + > +static void __init i2c_imx_set_clk(struct imx_i2c_struct *i2c_imx, > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0unsigned int rate) > +{ > + =C2=A0 =C2=A0 =C2=A0 unsigned long i2c_clk_rate =3D clk_get_rate(i2= c_imx->clk); > + =C2=A0 =C2=A0 =C2=A0 int i =3D find_div(i2c_clk_rate, rate); > > =C2=A0 =C2=A0 =C2=A0 =C2=A0/* Store divider value */ > =C2=A0 =C2=A0 =C2=A0 =C2=A0i2c_imx->ifdr =3D i2c_clk_div[i][1]; > @@ -271,10 +288,9 @@ static void __init i2c_imx_set_clk(struct imx_i2= c_struct *i2c_imx, > > =C2=A0 =C2=A0 =C2=A0 =C2=A0/* dev_dbg() can't be used, because adapte= r is not yet registered */ > =C2=A0#ifdef CONFIG_I2C_DEBUG_BUS > - =C2=A0 =C2=A0 =C2=A0 printk(KERN_DEBUG "I2C: <%s> I2C_CLK=3D%d, REQ= DIV=3D%d\n", > - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 __func__, i2c_clk_= rate, div); > - =C2=A0 =C2=A0 =C2=A0 printk(KERN_DEBUG "I2C: <%s> IFDR[IC]=3D0x%x, = REAL DIV=3D%d\n", > - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 __func__, i2c_clk_= div[i][1], i2c_clk_div[i][0]); > + =C2=A0 =C2=A0 =C2=A0 pr_debug("<%s> I2C_CLK=3D%ld, REQ RATE=3D%d, D= IV=3D%d, IFDR[IC]=3D0x%x\n", > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 __func__, i2c_clk_= rate, rate, > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 i2c_clk_div[i][0],= i2c_clk_div[i][1]); > =C2=A0#endif > =C2=A0} > > -- > 1.7.4.1 > >