Re: [PATCH] i2c: davinci: Fix bus rate calculation on Keystone SoC

[Sekhar Nori <nsekhar-l0cyMroinI0@public.gmane.org>]

On Thursday 18 June 2015 02:23 PM, Alexander Sverdlin wrote:
> According to KeyStone Architecture I2C User Guide,
> 
>                          module clock frequency
> master clock frequency = ----------------------
>                          (ICCL + 6) + (ICCH + 6)
> 
> i.e. "d" in i2c_davinci_calc_clk_dividers() should be fixed and
> not dependent from module clock prescaler PSC on these SoCs.
> 
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin-xNZwKgViW5gAvxtiuMwx3w@public.gmane.org>
> ---
> 
> RFC: If someone from TI has an idea how to improve the coverage of future Keystone
> revisions -- hints/patches are welcome. The current ID check is based on
> Davinci/Keystone datasheets and is at least working on real Keystone II.

+ Murali who works on Keystone devices in TI.

> 
>  drivers/i2c/busses/i2c-davinci.c |   10 ++++++++++
>  1 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c
> index 4a110af..3d78f6a 100644
> --- a/drivers/i2c/busses/i2c-davinci.c
> +++ b/drivers/i2c/busses/i2c-davinci.c
> @@ -60,6 +60,8 @@
>  #define DAVINCI_I2C_IVR_REG	0x28
>  #define DAVINCI_I2C_EMDR_REG	0x2c
>  #define DAVINCI_I2C_PSC_REG	0x30
> +#define DAVINCI_I2C_ICPID1_REG	0x34
> +#define DAVINCI_I2C_ICPID2_REG	0x38
>  #define DAVINCI_I2C_FUNC_REG	0x48
>  #define DAVINCI_I2C_DIR_REG	0x4c
>  #define DAVINCI_I2C_DIN_REG	0x50
> @@ -203,6 +205,9 @@ static void i2c_davinci_calc_clk_dividers(struct davinci_i2c_dev *dev)
>  	 * where if PSC == 0, d = 7,
>  	 *       if PSC == 1, d = 6
>  	 *       if PSC > 1 , d = 5
> +	 *
> +	 * Note:
> +	 * d is always 6 on Keystone I2C controller
>  	 */
> 
>  	/* get minimum of 7 MHz clock, but max of 12 MHz */
> @@ -211,6 +216,11 @@ static void i2c_davinci_calc_clk_dividers(struct davinci_i2c_dev *dev)
>  		psc++;	/* better to run under spec than over */
>  	d = (psc >= 2) ? 5 : 7 - psc;
> 
> +	if (davinci_i2c_read_reg(dev, DAVINCI_I2C_ICPID2_REG) == 0x2206) {
> +		dev_dbg(dev->dev, "Keystone SoC detected\n");
> +		d = 6;
> +	}

I think its better to use a different compatible string for i2c on
keystone devices rather than using a fixed hardcoded IP version.

Thanks,
Sekhar