Subject: [linux-sunxi] [PATCH] i2c: mv64xxx: The n clockdiv factor is 0 based on sunxi SoCs

From: [email-masked] (Olliver Schinagl)
Date: Sun, 27 Sep 2015 18:05:35 +0200

Hey Hans,

On 27-09-15 16:57, Hans de Goede wrote:
> According to the datasheets to n factor for dividing the tclk is
> 2 to the power n on Allwinner SoCs, not 2 to the power n + 1 as it is
> on other mv64xxx implementations.
Ah!
>
> I've contacted Allwinner about this and they have confirmed that the
> datasheet is correct.
>
> This commit fixes the clk-divider calculations for Allwinner SoCs
> accordingly.
So this explains why all my i2c frequenties are double of what I setup. 
Thanks for taking the time of figuring it out! I'll give it a test 
hopefully soon.

Olliver
>
> Signed-off-by: Hans de Goede <[email-masked]>
> ---
>   drivers/i2c/busses/i2c-mv64xxx.c | 27 ++++++++++++++++++---------
>   1 file changed, 18 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-mv64xxx.c b/drivers/i2c/busses/i2c-mv64xxx.c
> index 30059c1..e75cf6d 100644
> --- a/drivers/i2c/busses/i2c-mv64xxx.c
> +++ b/drivers/i2c/busses/i2c-mv64xxx.c
> @@ -146,6 +146,8 @@ struct mv64xxx_i2c_data {
>   	bool			errata_delay;
>   	struct reset_control	*rstc;
>   	bool			irq_clear_inverted;
> +	/* Clk div is 2 to the power n, not 2 to the power n + 1 */
> +	bool			clk_n_base_0;
>   };
>   
>   static struct mv64xxx_i2c_regs mv64xxx_i2c_regs_mv64xxx = {
> @@ -759,25 +761,29 @@ MODULE_DEVICE_TABLE(of, mv64xxx_i2c_of_match_table);
>   #ifdef CONFIG_OF
>   #ifdef CONFIG_HAVE_CLK
>   static int
> -mv64xxx_calc_freq(const int tclk, const int n, const int m)
> +mv64xxx_calc_freq(struct mv64xxx_i2c_data *drv_data,
> +		  const int tclk, const int n, const int m)
>   {
> -	return tclk / (10 * (m + 1) * (2 << n));
> +	if (drv_data->clk_n_base_0)
> +		return tclk / (10 * (m + 1) * (1 << n));
> +	else
> +		return tclk / (10 * (m + 1) * (2 << n));
>   }
>   
>   static bool
> -mv64xxx_find_baud_factors(const u32 req_freq, const u32 tclk, u32 *best_n,
> -			  u32 *best_m)
> +mv64xxx_find_baud_factors(struct mv64xxx_i2c_data *drv_data,
> +			  const u32 req_freq, const u32 tclk)
>   {
>   	int freq, delta, best_delta = INT_MAX;
>   	int m, n;
>   
>   	for (n = 0; n <= 7; n++)
>   		for (m = 0; m <= 15; m++) {
> -			freq = mv64xxx_calc_freq(tclk, n, m);
> +			freq = mv64xxx_calc_freq(drv_data, tclk, n, m);
>   			delta = req_freq - freq;
>   			if (delta >= 0 && delta < best_delta) {
> -				*best_m = m;
> -				*best_n = n;
> +				drv_data->freq_m = m;
> +				drv_data->freq_n = n;
>   				best_delta = delta;
>   			}
>   			if (best_delta == 0)
> @@ -815,8 +821,11 @@ mv64xxx_of_config(struct mv64xxx_i2c_data *drv_data,
>   	if (of_property_read_u32(np, "clock-frequency", &bus_freq))
>   		bus_freq = 100000; /* 100kHz by default */
>   
> -	if (!mv64xxx_find_baud_factors(bus_freq, tclk,
> -				       &drv_data->freq_n, &drv_data->freq_m)) {
> +	if (of_device_is_compatible(np, "allwinner,sun4i-a10-i2c") ||
> +	    of_device_is_compatible(np, "allwinner,sun6i-a31-i2c"))
> +		drv_data->clk_n_base_0 = true;
> +
> +	if (!mv64xxx_find_baud_factors(drv_data, bus_freq, tclk)) {
>   		rc = -EINVAL;
>   		goto out;
>   	}