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

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Date:   Fri, 19 Mar 2021 05:15:14 +0000
From:   Aisheng Dong <aisheng.dong@....com>
To:     Clark Wang <xiaoning.wang@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>
CC:     "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        "sumit.semwal@...aro.org" <sumit.semwal@...aro.org>,
        "christian.koenig@....com" <christian.koenig@....com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 09/11] i2c: imx-lpi2c: fix i2c timing issue

> From: Clark Wang <xiaoning.wang@....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@....com>
> Signed-off-by: Clark Wang <xiaoning.wang@....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?

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