[U-Boot] [PATCH v2] i2c: mvtwsi: Fix problem with baud rate calculation

[Hans de Goede]

Hi,

On 18-03-15 09:30, Stefan Roese wrote:
> The current implementation for baudrate calculation is incorrect.
> This part from the formula:
>
> "2 ^ (n + 1)" is not equivalent to (1 << n) but to (2 << n)!
>
> This patch fixes this and moves this calculation to a function instead of using a macro.
> This new function is taken from the Linux kernel.
>
> This was detected and tested on the Marvell Armada A38x DB-88F6820-GP eval board.
>
> Signed-off-by: Stefan Roese <sr at denx.de>
> Cc: Prafulla Wadaskar <prafulla at marvell.com>
> Cc: Luka Perkov <luka.perkov at sartura.hr>
> Cc: Hans de Goede <hdegoede at redhat.com>
> Cc: Ian Campbell <ijc at hellion.org.uk>
> Cc: Heiko Schocher <hs at denx.de>
> ---
> v2:
> - Still use the old formula for SUNXI, as this was checked
>    by Hans with Allwinner to be the correct formula. This means
>    that the Linux baudrate is incorrect for SUNXI I2C though.
>


Thanks for the v2. This looks good to me:

Acked-by: Hans de Goede <hdegoede at redhat.com>

Regards,

Hans

>   drivers/i2c/mvtwsi.c | 17 +++++++++--------
>   1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/i2c/mvtwsi.c b/drivers/i2c/mvtwsi.c
> index 9b2ca1e..6f6edd5 100644
> --- a/drivers/i2c/mvtwsi.c
> +++ b/drivers/i2c/mvtwsi.c
> @@ -228,13 +228,14 @@ static int twsi_stop(int status)
>   	return status;
>   }
>
> -/*
> - * Ugly formula to convert m and n values to a frequency comes from
> - * TWSI specifications
> - */
> -
> -#define TWSI_FREQUENCY(m, n) \
> -	(CONFIG_SYS_TCLK / (10 * (m + 1) * (1 << n)))
> +static unsigned int twsi_calc_freq(const int n, const int m)
> +{
> +#ifdef CONFIG_SUNXI
> +	return CONFIG_SYS_TCLK / (10 * (m + 1) * (1 << n));
> +#else
> +	return CONFIG_SYS_TCLK / (10 * (m + 1) * (2 << n));
> +#endif
> +}
>
>   /*
>    * Reset controller.
> @@ -266,7 +267,7 @@ static unsigned int twsi_i2c_set_bus_speed(struct i2c_adapter *adap,
>   	/* compute m, n setting for highest speed not above requested speed */
>   	for (n = 0; n < 8; n++) {
>   		for (m = 0; m < 16; m++) {
> -			tmp_speed = TWSI_FREQUENCY(m, n);
> +			tmp_speed = twsi_calc_freq(n, m);
>   			if ((tmp_speed <= requested_speed)
>   			 && (tmp_speed > highest_speed)) {
>   				highest_speed = tmp_speed;
>