Re: [PATCH v5] i2c: rk3x: adjust the LOW divison based on characteristics of SCL
Hi Addy,
On Monday 13 October 2014 at 10:44:04, Addy Ke wrote:
> As show in I2C specification:
> - Standard-mode: the minimum HIGH period of the scl clock is 4.0us
> the minimum LOW period of the scl clock is 4.7us
> - Fast-mode: the minimum HIGH period of the scl clock is 0.6us
> the minimum LOW period of the scl clock is 1.3us
>
> I have measured i2c SCL waveforms in fast-mode by oscilloscope
> on rk3288-pinky board. the LOW period of the scl clock is 1.3us.
> It is so critical that we must adjust LOW division to increase
> the LOW period of the scl clock.
>
> Thanks Doug for the suggestion about division formulas.
>
> Tested-by: Heiko Stuebner
> Reviewed-by: Doug Anderson
> Tested-by: Doug Anderson
> Signed-off-by: Addy Ke
> ---
> Changes in v2:
> - remove Fast-mode plus and HS-mode
> - use new formulas suggested by Doug
> Changes in V3:
> - use new formulas (sep 30) suggested by Doug
> Changes in V4:
> - fix some wrong style
> - WARN_ONCE if min_low_div > max_low_div
> Changes in V5:
> - round up for i2c_rate and round down for scl_rate, suggested by Max
> - place a WARN_ON if scl_rate < 1000, suggested by Max
> - add div_high and div_low overflow protection, suggested by Max
>
> drivers/i2c/busses/i2c-rk3x.c | 161
> +++--- 1 file changed, 152
> insertions(+), 9 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-rk3x.c b/drivers/i2c/busses/i2c-rk3x.c
> index b41d979..a30a4fb 100644
> --- a/drivers/i2c/busses/i2c-rk3x.c
> +++ b/drivers/i2c/busses/i2c-rk3x.c
> @@ -24,6 +24,7 @@
> #include
> #include
> #include
> +#include
>
>
> /* Register Map */
> @@ -428,18 +429,158 @@ out:
> return IRQ_HANDLED;
> }
>
> -static void rk3x_i2c_set_scl_rate(struct rk3x_i2c *i2c, unsigned long
> scl_rate) +static int rk3x_i2c_calc_divs(unsigned long i2c_rate, unsigned
> long scl_rate, + unsigned long *div_low, unsigned
> long
*div_high)
> {
> - unsigned long i2c_rate = clk_get_rate(i2c->clk);
> - unsigned int div;
> + unsigned long min_low_ns, min_high_ns;
> + unsigned long max_data_hold_ns;
> + unsigned long data_hold_buffer_ns;
> + unsigned long max_low_ns, min_total_ns;
> +
> + unsigned long i2c_rate_khz, scl_rate_khz;
> +
> + unsigned long min_low_div, min_high_div;
> + unsigned long max_low_div;
> +
> + unsigned long min_div_for_hold, min_total_div;
> + unsigned long extra_div, extra_low_div, ideal_low_div;
> +
> + /* Only support standard-mode and fast-mode */
> + if (WARN_ON(scl_rate > 40))
> + scl_rate = 40;
> +
> + /* prevent scl_rate_khz from becoming 0 */
> + if (WARN_ON(scl_rate < 1000))
> + scl_rate = 1000;
> +
> + /*
> + * min_low_ns: The minimum number of ns we need to hold low
> + * to meet i2c spec
> + * min_high_ns: The minimum number of ns we need to hold high
> + * to meet i2c spec
> + * max_low_ns: The maximum number of ns we can hold low
> + * to meet i2c spec
> + *
> + * Note: max_low_ns should be (max data hold time * 2 - buffer)
> + * This is because the i2c host on Rockchip holds the data line
> + * for half the low time.
> + */
> + if (scl_rate <= 10) {
> + min_low_ns = 4700;
> + min_high_ns = 4000;
> + max_data_hold_ns = 3450;
> + data_hold_buffer_ns = 50;
> + } else {
> + min_low_ns = 1300;
> + min_high_ns = 600;
> + max_data_hold_ns = 900;
> + data_hold_buffer_ns = 50;
> + }
> + max_low_ns = max_data_hold_ns * 2 - data_hold_buffer_ns;
> + min_total_ns = min_low_ns + min_high_ns;
> +
> + /* Adjust to avoid overflow */
> + i2c_rate_khz = DIV_ROUND_UP(i2c_rate, 1000);
> + scl_rate_khz = scl_rate / 1000;
>
> - /* set DIV = DIVH = DIVL
> - * SCL rate = (clk rate) / (8 * (DIVH + 1 + DIVL + 1))
> - * = (clk rate) / (16 * (DIV + 1))
> + /*
> + * We need the total div to be >= this number
> + * so we don't clock too fast.
> + */
> + min_total_div = DIV_ROUND_UP(i2c_rate_khz, scl_rate_khz * 8);
> +
> + /* These are the min dividers needed for min hold times. */
> + min_low_div = DIV_ROUND_UP(i2c_rate_khz * min_low_ns, 8 * 100);
> + min_high_div = DIV_ROUND_UP(i2c_rate_khz * min_high_ns, 8 * 100);
> + min_div_for_hold = (min_low_div + min_high_div);
> +
> + /*
> + * This is the maximum divider so we don't go over the max.
> + * We don't round up here (we round down) since this is a max.
>*/
> - div = DIV_ROUND_UP(i2c_rate, scl_rate * 16) - 1;
> + max_low_div = i2c_rate_khz * max_low_ns / (8 * 100);
> +
> + if (min_low_div > max_low_div) {
> + WARN_ONCE(true,
> + "Conflicting, min_low_div %lu, max_low_div %lu\
[PATCH v5] i2c: rk3x: adjust the LOW divison based on characteristics of SCL
As show in I2C specification:
- Standard-mode: the minimum HIGH period of the scl clock is 4.0us
the minimum LOW period of the scl clock is 4.7us
- Fast-mode: the minimum HIGH period of the scl clock is 0.6us
the minimum LOW period of the scl clock is 1.3us
I have measured i2c SCL waveforms in fast-mode by oscilloscope
on rk3288-pinky board. the LOW period of the scl clock is 1.3us.
It is so critical that we must adjust LOW division to increase
the LOW period of the scl clock.
Thanks Doug for the suggestion about division formulas.
Tested-by: Heiko Stuebner
Reviewed-by: Doug Anderson
Tested-by: Doug Anderson
Signed-off-by: Addy Ke
---
Changes in v2:
- remove Fast-mode plus and HS-mode
- use new formulas suggested by Doug
Changes in V3:
- use new formulas (sep 30) suggested by Doug
Changes in V4:
- fix some wrong style
- WARN_ONCE if min_low_div > max_low_div
Changes in V5:
- round up for i2c_rate and round down for scl_rate, suggested by Max
- place a WARN_ON if scl_rate < 1000, suggested by Max
- add div_high and div_low overflow protection, suggested by Max
drivers/i2c/busses/i2c-rk3x.c | 161 +++---
1 file changed, 152 insertions(+), 9 deletions(-)
diff --git a/drivers/i2c/busses/i2c-rk3x.c b/drivers/i2c/busses/i2c-rk3x.c
index b41d979..a30a4fb 100644
--- a/drivers/i2c/busses/i2c-rk3x.c
+++ b/drivers/i2c/busses/i2c-rk3x.c
@@ -24,6 +24,7 @@
#include
#include
#include
+#include
/* Register Map */
@@ -428,18 +429,158 @@ out:
return IRQ_HANDLED;
}
-static void rk3x_i2c_set_scl_rate(struct rk3x_i2c *i2c, unsigned long scl_rate)
+static int rk3x_i2c_calc_divs(unsigned long i2c_rate, unsigned long scl_rate,
+ unsigned long *div_low, unsigned long *div_high)
{
- unsigned long i2c_rate = clk_get_rate(i2c->clk);
- unsigned int div;
+ unsigned long min_low_ns, min_high_ns;
+ unsigned long max_data_hold_ns;
+ unsigned long data_hold_buffer_ns;
+ unsigned long max_low_ns, min_total_ns;
+
+ unsigned long i2c_rate_khz, scl_rate_khz;
+
+ unsigned long min_low_div, min_high_div;
+ unsigned long max_low_div;
+
+ unsigned long min_div_for_hold, min_total_div;
+ unsigned long extra_div, extra_low_div, ideal_low_div;
+
+ /* Only support standard-mode and fast-mode */
+ if (WARN_ON(scl_rate > 40))
+ scl_rate = 40;
+
+ /* prevent scl_rate_khz from becoming 0 */
+ if (WARN_ON(scl_rate < 1000))
+ scl_rate = 1000;
+
+ /*
+* min_low_ns: The minimum number of ns we need to hold low
+* to meet i2c spec
+* min_high_ns: The minimum number of ns we need to hold high
+* to meet i2c spec
+* max_low_ns: The maximum number of ns we can hold low
+* to meet i2c spec
+*
+* Note: max_low_ns should be (max data hold time * 2 - buffer)
+* This is because the i2c host on Rockchip holds the data line
+* for half the low time.
+*/
+ if (scl_rate <= 10) {
+ min_low_ns = 4700;
+ min_high_ns = 4000;
+ max_data_hold_ns = 3450;
+ data_hold_buffer_ns = 50;
+ } else {
+ min_low_ns = 1300;
+ min_high_ns = 600;
+ max_data_hold_ns = 900;
+ data_hold_buffer_ns = 50;
+ }
+ max_low_ns = max_data_hold_ns * 2 - data_hold_buffer_ns;
+ min_total_ns = min_low_ns + min_high_ns;
+
+ /* Adjust to avoid overflow */
+ i2c_rate_khz = DIV_ROUND_UP(i2c_rate, 1000);
+ scl_rate_khz = scl_rate / 1000;
- /* set DIV = DIVH = DIVL
-* SCL rate = (clk rate) / (8 * (DIVH + 1 + DIVL + 1))
-* = (clk rate) / (16 * (DIV + 1))
+ /*
+* We need the total div to be >= this number
+* so we don't clock too fast.
+*/
+ min_total_div = DIV_ROUND_UP(i2c_rate_khz, scl_rate_khz * 8);
+
+ /* These are the min dividers needed for min hold times. */
+ min_low_div = DIV_ROUND_UP(i2c_rate_khz * min_low_ns, 8 * 100);
+ min_high_div = DIV_ROUND_UP(i2c_rate_khz * min_high_ns, 8 * 100);
+ min_div_for_hold = (min_low_div + min_high_div);
+
+ /*
+* This is the maximum divider so we don't go over the max.
+* We don't round up here (we round down) since this is a max.
*/
- div = DIV_ROUND_UP(i2c_rate, scl_rate * 16) - 1;
+ max_low_div = i2c_rate_khz * max_low_ns / (8 * 100);
+
+ if (min_low_div > max_low_div) {
+ WARN_ONCE(true,
+ "Conflicting, min_low_div %lu, max_low_div %lu\n",
+ min_low_div, max_low_div);
+ max_low_div = min_low_div;
+ }
+
+ if (min_div_for_hold > min_total_div) {
+ /*
+
