Re: [PATCH 4/8] i2c: img-scb: fix LOW and HIGH period values for the SCL clock

[James Hogan <james.hogan@imgtec.com>]

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Hi Sifan,

On 27/07/15 12:47, Sifan Naeem wrote:
> After determining the minimum value for the High period (TCKH) the
> remainder of the internal clock pulses is set as the Low period (TCKL).
> This causes the i2c clock duty cycle to be much less than 50%.
> 
> The fix suggested here, start with TCKH and TCKL at 50% of the internal
> clock pulses and adjusts the TCKH and TCKL values from there if the
> minimum value for TCKL is not met. This will make sure the i2c clock
> duty cycle is at 50% or close 50% whenever possible.
> 
> Fixes: 27bce4 ("i2c: img-scb: Add Imagination Technologies I2C SCB driver")
> Signed-off-by: Sifan Naeem <sifan.naeem@imgtec.com>
> Cc: Stable kernel (v3.19+) <stable@vger.kernel.org>
> ---
>  drivers/i2c/busses/i2c-img-scb.c |   30 +++++++++++++++++-------------
>  1 file changed, 17 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-img-scb.c b/drivers/i2c/busses/i2c-img-scb.c
> index b4f59e1..51a5be8 100644
> --- a/drivers/i2c/busses/i2c-img-scb.c
> +++ b/drivers/i2c/busses/i2c-img-scb.c
> @@ -1178,25 +1178,29 @@ static int img_i2c_init(struct img_i2c *i2c)
>  	    ((bitrate_khz * clk_period) / 2))
>  		int_bitrate++;
>  
> -	/* Setup TCKH value */
> -	tckh = DIV_ROUND_UP(timing.tckh, clk_period);
> +	/*
> +	 * Setup clock duty cycle, start with 50% and adjust TCKH and TCKL
> +	 * values from there if they don't meet minimum timing requirements
> +	 */
> +	 tckh = int_bitrate / 2;
> +	 tckl = int_bitrate - tckh;

too much indentation here.

Otherwise looks good to me.

Acked-by: James Hogan <james.hogan@imgtec.com>

Cheers
James

>  
> -	if (tckh > 0)
> -		data = tckh - 1;
> -	else
> -		data = 0;
> +	/* Adjust TCKH and TCKL values */
> +	data = DIV_ROUND_UP(timing.tckl, clk_period);
>  
> -	img_i2c_writel(i2c, SCB_TIME_TCKH_REG, data);
> +	if (tckl < data) {
> +		tckl = data;
> +		tckh = int_bitrate - tckl;
> +	}
>  
> -	/* Setup TCKL value */
> -	tckl = int_bitrate - tckh;
> +	if (tckh > 0)
> +		--tckh;
>  
>  	if (tckl > 0)
> -		data = tckl - 1;
> -	else
> -		data = 0;
> +		--tckl;
>  
> -	img_i2c_writel(i2c, SCB_TIME_TCKL_REG, data);
> +	img_i2c_writel(i2c, SCB_TIME_TCKH_REG, tckh);
> +	img_i2c_writel(i2c, SCB_TIME_TCKL_REG, tckl);
>  
>  	/* Setup TSDH value */
>  	tsdh = DIV_ROUND_UP(timing.tsdh, clk_period);
> 


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