> -----Original Message----- > From: Aaro Koskinen [mailto:aaro.koskinen@xxxxxxxxx] > Subject: Re: [PATCH]i2c-omap: pass scll, sclh through board file for Errata > i585 > > Hi, > > balajitk@xxxxxx wrote: > > From: Balaji T K <balajitk@xxxxxx> > > > > Errata ID: i535 - I2C1 to 3 SCL low period is shorter in FS mode > > Due to IO cell influence, I2C1 to 3 SCL low period can be shorter than > expected. > > As a result, I2C AC timing (SCL minimum low period) in FS mode may not meet > > the timing configured by software. > > > > I2C1 to 3, SCL low period is programmable and proper adjustments > > to the SCLL/HSSCLL values can avoid the issue. > > > > This patch provides flexibility to control tLOW, tHIGH for different boards. > > scll, sclh values are to be provide in board data > > for differents modes (standard, fast and high speed mode) > > as the scl rate (I2C bus speed) can be changed by bootargs. > > This patch is very much needed, because these values are highly board > specific. > At the moment we are forced to patch the i2c bus driver when finetuning the > I2C > timings for a certain board, which is ugly. > > However, I have comment one about the implementation: > <snip> > I think it would be simpler if we move these calcuations into a function. > E.g. something like: > If the custom function is also to fine the scl low and scl high values. How about passing the Tlow to T, Thigh to T ratio. T = 1/100Khz , 1/400Khz , 1/HS speed to make things simpler. > if (dev->speed > 400) { > /* HS mode */ > pdata->set_scl(internal_clk, 400, &fsscll, &fssclh); > pdata->set_scl(fclk_rate, dev->speed, &hsscll, &hssclh); > } else { > /* Fast & standard mode */ > pdata->set_scl(internal_clk, dev->speed, &fsscll, &fssclh); > } > > Then the default function would be something like: > > static void omap_i2c_default_scl(unsigned clk, unsigned speed, u16 *scll, u16 > *sclh) > { > if (speed > 100) { > /* Fast & HS modes */ > unsigned scl = clk / speed; > > *scll = scl - (scl / 3) - 7; > *sclh = (scl / 3) - 5; > } else { > /* Standard mode */ > *scll = clk / (speed * 2) - 7; > *scll = clk / (speed * 2) - 5; > } > } > > And the platform data would just provide a board-specific function if needed. > > A. -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
