| Message ID | 1448578757-12613-6-git-send-email-wsa@the-dreams.de (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Simon Horman |
| Headers | show |
On Thu, Nov 26, 2015 at 11:59 PM, Wolfram Sang <wsa@the-dreams.de> wrote: > --- a/drivers/i2c/busses/i2c-rcar.c > +++ b/drivers/i2c/busses/i2c-rcar.c > @@ -211,12 +214,12 @@ static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv, struct i2c_timin > * it is impossible to calculate large scale > * number on u32. separate it > * > - * F[(ticf + tr + intd) * ick] > - * = F[(35 + 200 + 50)ns * ick] > - * = F[285 * ick / 1000000000] > - * = F[(ick / 1000000) * 285 / 1000] > + * F[(ticf + tr + intd) * ick] with sum = (ticf + tr + intd) > + * = F[sum * ick / 1000000000] > + * = F[(ick / 1000000) * sum / 1000] > */ > - round = (ick + 500000) / 1000000 * 285; > + sum = t->scl_fall_ns + t->scl_rise_ns + t->scl_int_delay_ns; > + round = (ick + 500000) / 1000000 * sum; If you're sure it cannot overflow, doing the "* sum" before the division improves accuracy. > round = (round + 500) / 1000; You can use DIV_ROUND_CLOSEST everywhere, e.g. round = DIV_ROUND_CLOSEST(round, 1000) Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org 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 -- To unsubscribe from this list: send the line "unsubscribe linux-sh" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi Geert, > > - round = (ick + 500000) / 1000000 * 285; > > + sum = t->scl_fall_ns + t->scl_rise_ns + t->scl_int_delay_ns; > > + round = (ick + 500000) / 1000000 * sum; > > If you're sure it cannot overflow, doing the "* sum" before the division > improves accuracy. Thanks for the input. In this patch, however, I intentionally did not change the formula but only replaced the constants with the now user supplied values. Everything else should be a separate patch IMO.
diff --git a/Documentation/devicetree/bindings/i2c/i2c-rcar.txt b/Documentation/devicetree/bindings/i2c/i2c-rcar.txt index ea406eb20fa5ad..95e97223a71c83 100644 --- a/Documentation/devicetree/bindings/i2c/i2c-rcar.txt +++ b/Documentation/devicetree/bindings/i2c/i2c-rcar.txt @@ -20,6 +20,10 @@ Optional properties: propoerty indicates the default frequency 100 kHz. - clocks: clock specifier. +- i2c-scl-falling-time-ns: see i2c.txt +- i2c-scl-internal-delay-ns: see i2c.txt +- i2c-scl-rising-time-ns: see i2c.txt + Examples : i2c0: i2c@e6508000 { diff --git a/drivers/i2c/busses/i2c-rcar.c b/drivers/i2c/busses/i2c-rcar.c index 453ce10132025d..9465a23bcc91a5 100644 --- a/drivers/i2c/busses/i2c-rcar.c +++ b/drivers/i2c/busses/i2c-rcar.c @@ -164,12 +164,15 @@ static int rcar_i2c_bus_barrier(struct rcar_i2c_priv *priv) static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv, struct i2c_timings *t) { - u32 scgd, cdf, round, ick, scl, cdf_width; + u32 scgd, cdf, round, ick, sum, scl, cdf_width; unsigned long rate; struct device *dev = rcar_i2c_priv_to_dev(priv); /* Fall back to previously used values if not supplied */ t->bus_freq = t->bus_freq ?: 100000; + t->scl_fall_ns = t->scl_fall_ns ?: 35; + t->scl_rise_ns = t->scl_rise_ns ?: 200; + t->scl_int_delay_ns = t->scl_int_delay_ns ?: 50; switch (priv->devtype) { case I2C_RCAR_GEN1: @@ -193,9 +196,9 @@ static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv, struct i2c_timin * SCL = ick / (20 + SCGD * 8 + F[(ticf + tr + intd) * ick]) * * ick : I2C internal clock < 20 MHz - * ticf : I2C SCL falling time = 35 ns here - * tr : I2C SCL rising time = 200 ns here - * intd : LSI internal delay = 50 ns here + * ticf : I2C SCL falling time + * tr : I2C SCL rising time + * intd : LSI internal delay * clkp : peripheral_clk * F[] : integer up-valuation */ @@ -211,12 +214,12 @@ static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv, struct i2c_timin * it is impossible to calculate large scale * number on u32. separate it * - * F[(ticf + tr + intd) * ick] - * = F[(35 + 200 + 50)ns * ick] - * = F[285 * ick / 1000000000] - * = F[(ick / 1000000) * 285 / 1000] + * F[(ticf + tr + intd) * ick] with sum = (ticf + tr + intd) + * = F[sum * ick / 1000000000] + * = F[(ick / 1000000) * sum / 1000] */ - round = (ick + 500000) / 1000000 * 285; + sum = t->scl_fall_ns + t->scl_rise_ns + t->scl_int_delay_ns; + round = (ick + 500000) / 1000000 * sum; round = (round + 500) / 1000; /*