On Fri, May 16, 2014 at 05:32:10PM +0200, Maxime COQUELIN wrote:
> The i2c timing values specified in the driver are the minimun
> values defined in the I2C specifications.
> The I2C specification does not specify any default or maximum values.
>
> Some I2C devices are out of spec, and might not work properly with minimum
> values.
Can you give names here? Would be interesting to know since a few
drivers implement the minimum timings.
> This patch adds a 10% margin on all the timings.
Is there a safety margin or do the devices start to work exactly at 10%?
>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@xxxxxx>
> ---
> drivers/i2c/busses/i2c-st.c | 24 ++++++++++++------------
> 1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-st.c b/drivers/i2c/busses/i2c-st.c
> index 8720161..09142f1 100644
> --- a/drivers/i2c/busses/i2c-st.c
> +++ b/drivers/i2c/busses/i2c-st.c
> @@ -210,21 +210,21 @@ static inline void st_i2c_clr_bits(void __iomem *reg, u32 mask)
> static struct st_i2c_timings i2c_timings[] = {
That needs a comment about the margin, otherwise people will wonder
where these values come from.
> [I2C_MODE_STANDARD] = {
> .rate = 100000,
> - .rep_start_hold = 4000,
> - .rep_start_setup = 4700,
> - .start_hold = 4000,
> - .data_setup_time = 250,
> - .stop_setup_time = 4000,
> - .bus_free_time = 4700,
> + .rep_start_hold = 4400,
> + .rep_start_setup = 5170,
> + .start_hold = 4400,
> + .data_setup_time = 275,
> + .stop_setup_time = 4400,
> + .bus_free_time = 5170,
> },
> [I2C_MODE_FAST] = {
> .rate = 400000,
> - .rep_start_hold = 600,
> - .rep_start_setup = 600,
> - .start_hold = 600,
> - .data_setup_time = 100,
> - .stop_setup_time = 600,
> - .bus_free_time = 1300,
> + .rep_start_hold = 660,
> + .rep_start_setup = 660,
> + .start_hold = 660,
> + .data_setup_time = 110,
> + .stop_setup_time = 660,
> + .bus_free_time = 1430,
> },
> };
>
> --
> 1.9.1
>
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