[PATCH 09/11] i2c: imx-lpi2c: fix i2c timing issue

[Clark Wang]

> -----Original Message-----
> From: Aisheng Dong <aisheng.dong at nxp.com>
> Sent: Friday, March 19, 2021 13:15
> To: Clark Wang <xiaoning.wang at nxp.com>; shawnguo at kernel.org;
> s.hauer at pengutronix.de
> Cc: kernel at pengutronix.de; festevam at gmail.com; dl-linux-imx <linux-
> imx at nxp.com>; sumit.semwal at linaro.org; christian.koenig at amd.com;
> linux-i2c at vger.kernel.org; linux-arm-kernel at lists.infradead.org; linux-
> kernel at vger.kernel.org
> Subject: RE: [PATCH 09/11] i2c: imx-lpi2c: fix i2c timing issue
>
> > From: Clark Wang <xiaoning.wang at nxp.com>
> > Sent: Wednesday, March 17, 2021 2:54 PM
> >
> > The clkhi and clklo ratio was not very precise before that can make
> > the time of START/STOP/HIGH LEVEL out of specification.
> >
> > Therefore, the calculation of these times has been modified in this patch.
> > At the same time, the mode rate definition of i2c is corrected.
> >
> > Reviewed-by: Fugang Duan <fugang.duan at nxp.com>
> > Signed-off-by: Clark Wang <xiaoning.wang at nxp.com>
> > ---
> >  drivers/i2c/busses/i2c-imx-lpi2c.c | 27 ++++++++++++++-------------
> >  1 file changed, 14 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c
> > b/drivers/i2c/busses/i2c-imx-lpi2c.c
> > index 7216a393095d..5dbe85126f24 100644
> > --- a/drivers/i2c/busses/i2c-imx-lpi2c.c
> > +++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
> > @@ -73,17 +73,17 @@
> >  #define MCFGR1_IGNACK	BIT(9)
> >  #define MRDR_RXEMPTY	BIT(14)
> >
> > -#define I2C_CLK_RATIO	2
> > +#define I2C_CLK_RATIO	24 / 59
>
> Where is this ratio coming from?
> Can you describe why use it in commit message?

This ratio is a value obtained after passing the test.
I2C's Tlow should longer than the spec.
For example, in FAST mode, Tlow should be longer than 1.3us.
The previous calculation violated the spec.
So I re-write the calculation of clk_cycle by referring the RM. Then test the 
ratio to let Tlow match the spec by catching the waveform.

Best Regards,
Clark Wang

>
> Regards
> Aisheng
>
> >  #define CHUNK_DATA	256
> >
> >  #define I2C_PM_TIMEOUT		1000 /* ms */
> >
> >  enum lpi2c_imx_mode {
> > -	STANDARD,	/* 100+Kbps */
> > -	FAST,		/* 400+Kbps */
> > -	FAST_PLUS,	/* 1.0+Mbps */
> > -	HS,		/* 3.4+Mbps */
> > -	ULTRA_FAST,	/* 5.0+Mbps */
> > +	STANDARD,	/* <=100Kbps */
> > +	FAST,		/* <=400Kbps */
> > +	FAST_PLUS,	/* <=1.0Mbps */
> > +	HS,		/* <=3.4Mbps */
> > +	ULTRA_FAST,	/* <=5.0Mbps */
> >  };
> >
> >  enum lpi2c_imx_pincfg {
> > @@ -156,13 +156,13 @@ static void lpi2c_imx_set_mode(struct
> > lpi2c_imx_struct *lpi2c_imx)
> >  	unsigned int bitrate = lpi2c_imx->bitrate;
> >  	enum lpi2c_imx_mode mode;
> >
> > -	if (bitrate < I2C_MAX_FAST_MODE_FREQ)
> > +	if (bitrate <= I2C_MAX_STANDARD_MODE_FREQ)
> >  		mode = STANDARD;
> > -	else if (bitrate < I2C_MAX_FAST_MODE_PLUS_FREQ)
> > +	else if (bitrate <= I2C_MAX_FAST_MODE_FREQ)
> >  		mode = FAST;
> > -	else if (bitrate < I2C_MAX_HIGH_SPEED_MODE_FREQ)
> > +	else if (bitrate <= I2C_MAX_FAST_MODE_PLUS_FREQ)
> >  		mode = FAST_PLUS;
> > -	else if (bitrate < I2C_MAX_ULTRA_FAST_MODE_FREQ)
> > +	else if (bitrate <= I2C_MAX_HIGH_SPEED_MODE_FREQ)
> >  		mode = HS;
> >  	else
> >  		mode = ULTRA_FAST;
> > @@ -209,7 +209,8 @@ static void lpi2c_imx_stop(struct lpi2c_imx_struct
> > *lpi2c_imx)
> >  	} while (1);
> >  }
> >
> > -/* CLKLO = I2C_CLK_RATIO * CLKHI, SETHOLD = CLKHI, DATAVD = CLKHI/2
> > */
> > +/* CLKLO = (1 - I2C_CLK_RATIO) * clk_cycle, SETHOLD = CLKHI, DATAVD =
> > CLKHI/2
> > +   CLKHI = I2C_CLK_RATIO * clk_cycle */
> >  static int lpi2c_imx_config(struct lpi2c_imx_struct *lpi2c_imx)  {
> >  	u8 prescale, filt, sethold, clkhi, clklo, datavd; @@ -232,8 +233,8
> > @@ static int lpi2c_imx_config(struct lpi2c_imx_struct *lpi2c_imx)
> >
> >  	for (prescale = 0; prescale <= 7; prescale++) {
> >  		clk_cycle = clk_rate / ((1 << prescale) * lpi2c_imx->bitrate)
> > -			    - 3 - (filt >> 1);
> > -		clkhi = (clk_cycle + I2C_CLK_RATIO) / (I2C_CLK_RATIO + 1);
> > +			    - (2 + filt) / (1 << prescale);
> > +		clkhi = clk_cycle * I2C_CLK_RATIO;
> >  		clklo = clk_cycle - clkhi;
> >  		if (clklo < 64)
> >  			break;
> > --
> > 2.25.1

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