On Mon, 2020-05-18 at 17:44 +0200, Geert Uytterhoeven wrote:
> 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?
>
(1000000000 * (sample_cnt + 1)) / clk_src value is a 32-bit, (1000000000
* (sample_cnt + 1)) will over 32-bit if sample_cnt is 7.
I think 1000000000 and clk_src is too big, maybe I can reduce then with
be divided all by 1000.
example:
unsigned int sample_ns;
unsigned int clk_src_khz = clk_src / 1000;
if(clk_src_khz)
sample_ns = (1000000 * (sample_cnt + 1)) / clk_src_khz;
else
return -EINVAL;
> > + 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
