Hello Eddie, On Wed, May 20, 2015 at 10:40:11AM +0800, Eddie Huang wrote: > On Mon, 2015-05-18 at 20:43 +0200, Uwe Kleine-König wrote: > > On Tue, May 19, 2015 at 12:40:08AM +0800, Eddie Huang wrote: > > > +/* calculate i2c port speed */ > > It would be nice to summarize the clock frequency settings here. > > Something like: > > > > /* > > * The input clock is divided by the value specified in the > > * device tree as clock-div. The actual bus speed is then > > * derived from this frequency by the following formula: > > * .... > > > > This would make it possible to verify your calculations below. > > The comment will be: > /* > * khz: I2C bus clock > * hclk: The input clock is divided by the value specified in the > * device tree as clock-div and which one of the two clocks you're writing about is hclk now? I assume the divided one. > * div = (sample_cnt + 1) * (step_cnt + 1) > * khz = (hclk / 2) / div khz for the 2nd time. > * > * The calculation is to get div value that let result of > * ((hclk / 2) / div) most approach and less than khz > */ I imagined something more hardware related. A list of register (or register bit fields) that influence the frequency and a formula i2c_freq = parent_clk / clock-div * (...) (It seems to be a bit more complicated here as there are two registers involved that are set differently depending on the target frequency.) > > > +static int mtk_i2c_set_speed(struct mtk_i2c *i2c, unsigned int clk_src_in_hz) clk_src_in_hz is the module's input rate already divided by clock-div. This clock-div value is fixed in hardware and unchangeable, right? Maybe give that divided clock a nice name? The target frequency is i2c->speed_hz, so among the possible frequencies we want to pick the highest one that is still less than or equal i2c->speed_hz, right? > > > + /* Set the hign speed mode register */ I just notice s/hign/high/ here. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ | -- 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
