Hi,
Please see my reply below (I skip comments that already reply in another
mail).
On Wed, 2015-05-20 at 10:57 +0200, Uwe Kleine-König wrote:
> Hello,
>
> now that I understood the formula some more comments to the calculation.
>
> On Tue, May 19, 2015 at 12:40:08AM +0800, Eddie Huang wrote:
> > +#define I2C_DEFAUT_SPEED 100000 /* hz */
> DEFAULT?
>
Yes, will fix.
> > +#define MAX_FS_MODE_SPEED 400000
> > +#define MAX_HS_MODE_SPEED 3400000
> > +#define MAX_SAMPLE_CNT_DIV 8
> > +#define MAX_STEP_CNT_DIV 64
> > +#define MAX_HS_STEP_CNT_DIV 8
> > [...]
> > +/* calculate i2c port speed */
> > +static int mtk_i2c_set_speed(struct mtk_i2c *i2c, unsigned int clk_src_in_hz)
> > +{
> add a comment here, that clk_src_in_hz is the parent clock already
> divided by clock-div.
>
We move parent_clk div clock-div in mtk_i2c_set_speed function, I think
this is more clear.
> > + step_div = max_step_cnt;
> > + /* Find the best combination */
> > + khz = i2c->speed_hz / 1000;
> > + hclk = clk_src_in_hz / 1000;
> Why are you dividing here? There shouldn't be an overflow problem and
> you're loosing precision.
OK, will remove div 1000.
>
> > + min_div = ((hclk >> 1) + khz - 1) / khz;
> The shift accounts for the fixed divider 2 in
>
> i2c_bus_freq = parent_clk / (clock-div * 2 * sample_cnt * step_cnt
>
> ? Maybe better call this opt_div instead of min_div?
OK
>
> > + best_mul = MAX_SAMPLE_CNT_DIV * max_step_cnt;
> > +
> > + for (sample_cnt = 1; sample_cnt <= MAX_SAMPLE_CNT_DIV; sample_cnt++) {
> > + step_cnt = (min_div + sample_cnt - 1) / sample_cnt;
> DIV_ROUND_UP
OK
> > +
> > + if (cnt_mul < best_mul) {
> > + best_mul = cnt_mul;
> > + sample_div = sample_cnt;
> > + step_div = step_cnt;
> I'd call these best_sample_cnt and best_step_cnt instead of sample_div
> and step_div.
OK
>
> > + if (best_mul == min_div)
> > + break;
> > + }
> > + }
> > +
> > + sample_cnt = sample_div;
> > + step_cnt = step_div;
> > + sclk = hclk / (2 * sample_cnt * step_cnt);
> > + if (sclk > khz) {
> Can this happen? A better name for "sclk" would be "bus_freq"?
Yes, if i2c->speed_hz is too small, not able to get target_speed using
hardware div.
>
> > + dev_dbg(i2c->dev, "%s mode: unsupported speed (%ldkhz)\n",
> > + (i2c->speed_hz > MAX_HS_MODE_SPEED) ? "HS" : "ST/FT",
> What is ST/FR? I would have expected FS here.
Please skip it.The debug message is too lousy.
>
> > + (long int)khz);
> > + return -EINVAL;
> > + }
> > +
> > + step_cnt--;
> > + sample_cnt--;
> > +
> > + if (i2c->speed_hz > MAX_FS_MODE_SPEED) {
> > + /* Set the hign speed mode register */
> > + i2c->timing_reg = I2C_FS_TIME_INIT_VALUE;
> > + i2c->high_speed_reg = I2C_TIME_DEFAULT_VALUE |
> > + (sample_cnt & I2C_TIMING_SAMPLE_COUNT_MASK) << 12 |
> > + (step_cnt & I2C_TIMING_SAMPLE_COUNT_MASK) << 8;
> > + } else {
> > + i2c->timing_reg =
> > + (sample_cnt & I2C_TIMING_SAMPLE_COUNT_MASK) << 8 |
> > + (step_cnt & I2C_TIMING_STEP_DIV_MASK) << 0;
> > + /* Disable the high speed transaction */
> > + i2c->high_speed_reg = I2C_TIME_CLR_VALUE;
> > + }
> Would it be sensible to write these values directly into hardware here?
No.In some error cases, we want to reinitialize hardware, keep these
values to avoid calculate again.
Eddie
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