On Thu, May 14, 2020 at 3:13 PM Qii Wang <qii.wang@xxxxxxxxxxxx> wrote:
> This patch adds a algorithm to calculate some ac-timing parameters
> which can fully meet I2C Spec.
>
> Signed-off-by: Qii Wang <qii.wang@xxxxxxxxxxxx>
> ---
> drivers/i2c/busses/i2c-mt65xx.c | 328 +++++++++++++++++++++++++++++++++-------
> 1 file changed, 277 insertions(+), 51 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-mt65xx.c b/drivers/i2c/busses/i2c-mt65xx.c
> index 0ca6c38a..7020618 100644
> --- a/drivers/i2c/busses/i2c-mt65xx.c
> +++ b/drivers/i2c/busses/i2c-mt65xx.c
> +/*
> + * Check and Calculate i2c ac-timing
> + *
> + * Hardware design:
> + * sample_ns = (1000000000 * (sample_cnt + 1)) / clk_src
> + * xxx_cnt_div = spec->min_xxx_ns / sample_ns
> + *
> + * Sample_ns is rounded down for xxx_cnt_div would be greater
> + * than the smallest spec.
> + * The sda_timing is chosen as the middle value between
> + * the largest and smallest.
> + */
> +static int mtk_i2c_check_ac_timing(struct mtk_i2c *i2c,
> + unsigned int clk_src,
> + unsigned int check_speed,
> + unsigned int step_cnt,
> + unsigned int sample_cnt)
> +{
> + const struct i2c_spec_values *spec;
> + unsigned int su_sta_cnt, low_cnt, high_cnt, max_step_cnt;
> + unsigned int sda_max, sda_min, clk_ns, max_sta_cnt = 0x3f;
> + long long sample_ns = (1000000000 * (sample_cnt + 1)) / clk_src;
So sample_ns is a 64-bit value. Is that really needed?
> + if (!i2c->dev_comp->timing_adjust)
> + return 0;
> +
> + if (i2c->dev_comp->ltiming_adjust)
> + max_sta_cnt = 0x100;
> +
> + spec = mtk_i2c_get_spec(check_speed);
> +
> + if (i2c->dev_comp->ltiming_adjust)
> + clk_ns = 1000000000 / clk_src;
> + else
> + clk_ns = sample_ns / 2;
> +
> + su_sta_cnt = DIV_ROUND_UP(spec->min_su_sta_ns, clk_ns);
> + if (su_sta_cnt > max_sta_cnt)
> + return -1;
> +
> + low_cnt = DIV_ROUND_UP(spec->min_low_ns, sample_ns);
So this is a 32-bit by 64-bit division (indeed, not 64-by-32!)
noreply@xxxxxxxxxxxxxx reports:
ERROR: modpost: "__udivdi3" [drivers/i2c/busses/i2c-mt65xx.ko] undefined!
ERROR: modpost: "__divdi3" [drivers/i2c/busses/i2c-mt65xx.ko] undefined!
for 32-bit builds.
> + max_step_cnt = mtk_i2c_max_step_cnt(check_speed);
> + if ((2 * step_cnt) > low_cnt && low_cnt < max_step_cnt) {
> + if (low_cnt > step_cnt) {
> + high_cnt = 2 * step_cnt - low_cnt;
> + } else {
> + high_cnt = step_cnt;
> + low_cnt = step_cnt;
> + }
> + } else {
> + return -2;
> + }
> +
> + sda_max = spec->max_hd_dat_ns / sample_ns;
> + if (sda_max > low_cnt)
> + sda_max = 0;
> +
> + sda_min = DIV_ROUND_UP(spec->min_su_dat_ns, sample_ns);
One more.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
