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 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html