Re: [PATCH 04/12] i2c: meson: use full 12 bits for clock divider

[Jerome Brunet <jbrunet@baylibre.com>]

On Wed, 2017-03-08 at 07:44 +0100, Heiner Kallweit wrote:
> The clock divider has 12 bits, splitted into a 10 bit field and a
> 2 bit field. The extra 2 bits aren't used currently.
> 
> Change this to use the full 12 bits and warn if the requested
> frequency is too low.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> ---
>  drivers/i2c/busses/i2c-meson.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-meson.c b/drivers/i2c/busses/i2c-meson.c
> index 5e243efa..a5764be5 100644
> --- a/drivers/i2c/busses/i2c-meson.c
> +++ b/drivers/i2c/busses/i2c-meson.c
> @@ -35,7 +35,9 @@
>  #define REG_CTRL_STATUS		BIT(2)
>  #define REG_CTRL_ERROR		BIT(3)
>  #define REG_CTRL_CLKDIV_SHIFT	12
> -#define REG_CTRL_CLKDIV_MASK	((BIT(10) - 1) << REG_CTRL_CLKDIV_SHIFT)
> +#define REG_CTRL_CLKDIV_MASK	GENMASK(21, 12)
> +#define REG_CTRL_CLKDIVEXT_SHIFT 28
> +#define REG_CTRL_CLKDIVEXT_MASK	GENMASK(29, 28)
>  
>  #define I2C_TIMEOUT_MS		500
>  
> @@ -136,8 +138,15 @@ static void meson_i2c_set_clk_div(struct meson_i2c *i2c)
>  	unsigned int div;
>  
>  	div = DIV_ROUND_UP(clk_rate, i2c->timings.bus_freq_hz * 4);
> +
> +	/* clock divider has 12 bits */
> +	WARN_ON(div >= (1 << 12));
> +
>  	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIV_MASK,
> -			   div << REG_CTRL_CLKDIV_SHIFT);
> +			   (div & GENMASK(9, 0)) << REG_CTRL_CLKDIV_SHIFT);
> +
> +	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIVEXT_MASK,
> +			   (div >> 10) << REG_CTRL_CLKDIVEXT_SHIFT);
>  
>  	dev_dbg(i2c->dev, "%s: clk %lu, freq %u, div %u\n", __func__,
>  		clk_rate, i2c->timings.bus_freq_hz, div);

Acked-by: Jerome Brunet <jbrunet@baylibre.com>