[PATCH v3 3/4] i2c: rk3x: new method to caculate i2c clocks
Andy Shevchenko
andy.shevchenko at gmail.com
Thu Jan 14 05:29:30 PST 2016
On Thu, Jan 14, 2016 at 2:31 PM, David Wu <david.wu at rock-chips.com> wrote:
> There was an timing issue about "repeated start" time at the I2C
> controller of version0, controller appears to drop SDA at .875x (7/8)
> programmed clk high. The rule(.875x) isn't enough to meet tSU;STA
> requirements on 100k's Standard-mode. To resolve this issue,
> data_upd_st, start_setup_cnt and stop_setup_cnt configs for I2C
> timing information are added, new rules are designed to calculate
> the timing information at new v1.
> --- a/drivers/i2c/busses/i2c-rk3x.c
> +++ b/drivers/i2c/busses/i2c-rk3x.c
> @@ -58,10 +58,15 @@ enum {
> #define REG_CON_LASTACK BIT(5) /* 1: send NACK after last received byte */
> #define REG_CON_ACTACK BIT(6) /* 1: stop if NACK is received */
>
> +#define REG_CON_SDA_CNT(cnt) ((cnt) << 8)
> +#define REG_CON_STA_CNT(cnt) ((cnt) << 12)
> +#define REG_CON_STO_CNT(cnt) ((cnt) << 14)
> +
> #define VERSION_MASK GENMASK(31, 16)
> #define VERSION_SHIFT 16
>
> #define RK3X_I2C_V0 0x0
> +#define RK3X_I2C_V1 0x1
>
> /* REG_MRXADDR bits */
> #define REG_MRXADDR_VALID(x) BIT(24 + (x)) /* [x*8+7:x*8] of MRX[R]ADDR valid */
> @@ -99,10 +104,16 @@ struct rk3x_i2c_soc_data {
> * struct rk3x_priv_i2c_timings - rk3x I2C timing information
> * @div_low: Divider output for low
> * @div_high: Divider output for high
> + * @thd_sda_count: SDA update point config used to adjust sda setup/hold time
> + * @tsu_sta_count: Start setup config for setup start time and hold start time
> + * @tsu_sto_count: Stop setup config for setup stop time
> */
> struct rk3x_priv_i2c_timings {
> unsigned long div_low;
> unsigned long div_high;
> + unsigned int thd_sda_count;
> + unsigned int tsu_sta_count;
> + unsigned int tsu_sto_count;
> };
And in this (or even separate) patch makes sense to introduce
extension structure, which is struct rk3x_priv_i2c_timings.
> struct rk3x_i2c_ops {
> @@ -154,6 +165,13 @@ static inline u32 i2c_readl(struct rk3x_i2c *i2c, unsigned int offset)
> return readl(i2c->regs + offset);
> }
>
> +static inline u32 rk3x_i2c_get_con_count(struct rk3x_i2c *i2c)
> +{
> + return REG_CON_SDA_CNT(i2c->t_priv.thd_sda_count) |
> + REG_CON_STA_CNT(i2c->t_priv.tsu_sta_count) |
> + REG_CON_STO_CNT(i2c->t_priv.tsu_sto_count);
> +}
> +
> /* Reset all interrupt pending bits */
> static inline void rk3x_i2c_clean_ipd(struct rk3x_i2c *i2c)
> {
> @@ -165,13 +183,13 @@ static inline void rk3x_i2c_clean_ipd(struct rk3x_i2c *i2c)
> */
> static void rk3x_i2c_start(struct rk3x_i2c *i2c)
> {
> - u32 val;
> + u32 val = rk3x_i2c_get_con_count(i2c);
>
> rk3x_i2c_clean_ipd(i2c);
> i2c_writel(i2c, REG_INT_START, REG_IEN);
>
> /* enable adapter with correct mode, send START condition */
> - val = REG_CON_EN | REG_CON_MOD(i2c->mode) | REG_CON_START;
> + val = val | REG_CON_EN | REG_CON_MOD(i2c->mode) | REG_CON_START;
>
> /* if we want to react to NACK, set ACTACK bit */
> if (!(i2c->msg->flags & I2C_M_IGNORE_NAK))
> @@ -212,7 +230,7 @@ static void rk3x_i2c_stop(struct rk3x_i2c *i2c, int error)
> * get the intended effect by resetting its internal state
> * and issuing an ordinary START.
> */
> - i2c_writel(i2c, 0, REG_CON);
> + i2c_writel(i2c, rk3x_i2c_get_con_count(i2c), REG_CON);
>
> /* signal that we are finished with the current msg */
> wake_up(&i2c->wait);
> @@ -630,6 +648,211 @@ static int rk3x_i2c_v0_calc_clock(unsigned long clk_rate,
> return ret;
> }
>
> +/**
> + * Calculate timing clock info values for desired SCL frequency
> + *
> + * @clk_rate: I2C input clock rate
> + * @t_input: Known I2C timing information
> + * @t_output: Caculated rk3x private timing information that would
> + * be written into regs
> + * Returns: 0 on success, -EINVAL if the goal SCL rate is too slow. In that case
> + * a best-effort divider value is returned in divs. If the target rate is
> + * too high, we silently use the highest possible rate.
> + * The following formulas are v1's method to calculate clock.
> + *
> + * l = divl + 1;
> + * h = divh + 1;
> + * s = data_upd_st + 1;
> + * u = start_setup_cnt + 1;
> + * p = stop_setup_cnt + 1;
> + * T = Tclk_i2c;
> +
> + * tHigh = 8 * h * T;
> + * tLow = 8 * l * T;
> +
> + * tHD;sda = (l * s + 1) * T;
> + * tSU;sda = [(8 - s) * l + 1] * T;
> + * tI2C = 8 * (l + h) * T;
> +
> + * tSU;sta = (8h * u + 1) * T;
> + * tHD;sta = [8h * (u + 1) - 1] * T;
> + * tSU;sto = (8h * p + 1) * T;
> + */
> +static int rk3x_i2c_v1_calc_clock(unsigned long clk_rate,
> + struct i2c_timings *t_input,
> + struct rk3x_priv_i2c_timings *t_output)
> +{
I see some similarities with existing code for v0. Can be refactored?
> + unsigned long spec_min_low_ns, spec_min_high_ns;
> + unsigned long spec_min_setup_start_ns, spec_min_stop_setup_ns;
> + unsigned long spec_min_data_setup_ns, spec_max_data_hold_ns;
> +
> + unsigned long min_low_ns, min_high_ns, min_total_ns;
> + unsigned long min_setup_start_ns, min_setup_data_ns;
> + unsigned long min_stop_setup_ns, max_hold_data_ns;
> +
> + unsigned long clk_rate_khz, scl_rate_khz;
> +
> + unsigned long min_low_div, min_high_div;
> +
> + unsigned long min_div_for_hold, min_total_div;
> + unsigned long extra_div, extra_low_div;
> + unsigned long data_hd_cnt;
> +
> + int ret = 0;
> +
> + /* Support standard-mode and fast-mode */
> + if (WARN_ON(t_input->bus_freq_hz > 400000))
> + t_input->bus_freq_hz = 400000;
> +
> + /* prevent scl_rate_khz from becoming 0 */
> + if (WARN_ON(t_input->bus_freq_hz < 1000))
> + t_input->bus_freq_hz = 1000;
> +
> + /*
> + * min_low_ns: The minimum number of ns we need to hold low to
> + * meet I2C specification, should include fall time.
> + * min_high_ns: The minimum number of ns we need to hold high to
> + * meet I2C specification, should include rise time.
> + */
> + if (t_input->bus_freq_hz <= 100000) {
> + spec_min_low_ns = 4700;
> + spec_min_high_ns = 4000;
> +
> + spec_min_setup_start_ns = 4700;
> + spec_min_stop_setup_ns = 4000;
> +
> + spec_min_data_setup_ns = 250;
> + spec_max_data_hold_ns = 3450;
> + } else if (t_input->bus_freq_hz <= 400000) {
> + spec_min_low_ns = 1300;
> + spec_min_high_ns = 600;
> +
> + spec_min_setup_start_ns = 600;
> + spec_min_stop_setup_ns = 600;
> +
> + spec_min_data_setup_ns = 100;
> + spec_max_data_hold_ns = 900;
> + }
> +
> + /* caculate min-divh and min-divl */
> + clk_rate_khz = DIV_ROUND_UP(clk_rate, 1000);
> + scl_rate_khz = t_input->bus_freq_hz / 1000;
> + min_total_div = DIV_ROUND_UP(clk_rate_khz, scl_rate_khz * 8);
> +
> + min_high_ns = t_input->scl_rise_ns + spec_min_high_ns;
> + min_high_div = DIV_ROUND_UP(clk_rate_khz * min_high_ns, 8 * 1000000);
> +
> + min_low_ns = t_input->scl_fall_ns + spec_min_low_ns;
> + min_low_div = DIV_ROUND_UP(clk_rate_khz * min_low_ns, 8 * 1000000);
> +
> + /* Final divh and divl must be greater than 0, otherwise the
> + * hardware would not output the i2c clk.
> + */
> + if (min_high_div <= 1)
> + min_high_div = 2;
> + if (min_low_div <= 1)
> + min_low_div = 2;
> +
> + /* These are the min dividers needed for min hold times. */
> + min_div_for_hold = (min_low_div + min_high_div);
> + min_total_ns = min_low_ns + min_high_ns;
> +
> + /*
> + * This is the maximum divider so we don't go over the maximum.
> + * We don't round up here (we round down) since this is a maximum.
> + */
> + if (min_div_for_hold >= min_total_div) {
> + /*
> + * Time needed to meet hold requirements is important.
> + * Just use that.
> + */
> + t_output->div_low = min_low_div;
> + t_output->div_high = min_high_div;
> + } else {
> + /*
> + * We've got to distribute some time among the low and high
> + * so we don't run too fast.
> + * We'll try to split things up by the scale of min_low_div and
> + * min_high_div, biasing slightly towards having a higher div
> + * for low (spend more time low).
> + */
> + extra_div = min_total_div - min_div_for_hold;
> + extra_low_div = DIV_ROUND_UP(min_low_div * extra_div,
> + min_div_for_hold);
> +
> + t_output->div_low = min_low_div + extra_low_div;
> + t_output->div_high = min_high_div + (extra_div - extra_low_div);
> + }
> +
> + /*
> + * calculate sda data hold count by the rules, thd_sda_count:3
> + * is a appropriate value to reduce calculated times.
> + * tHD;sda = (l * s + 1) * T
> + * tSU;sda = ((8 - s) * l + 1) * T
> + */
> + for (data_hd_cnt = 3; data_hd_cnt >= 0; data_hd_cnt--) {
> + max_hold_data_ns = DIV_ROUND_UP((data_hd_cnt
> + * (t_output->div_low) + 1)
> + * 1000000, clk_rate_khz);
> + min_setup_data_ns = DIV_ROUND_UP(((8 - data_hd_cnt)
> + * (t_output->div_low) + 1)
> + * 1000000, clk_rate_khz);
> + if ((max_hold_data_ns < spec_max_data_hold_ns) &&
> + (min_setup_data_ns > spec_min_data_setup_ns)) {
> + t_output->thd_sda_count = data_hd_cnt;
> + break;
> + }
> + }
> +
> + /*
> + * calculate start setup count, and we aren't care tHD;STA.
> + * If the start setup count meets the rule of tSU;sta, it also
> + * meets the rule of tHD;STA.
> + * tSU;sta = (8h * u + 1) * T
> + * tHD;sta = [8h * (u + 1) - 1] * T
> + */
> + min_setup_start_ns = t_input->scl_rise_ns + spec_min_setup_start_ns;
> + t_output->tsu_sta_count = DIV_ROUND_UP(clk_rate_khz * min_setup_start_ns
> + - 1000000, 8 * 1000000 * (t_output->div_high));
> +
> + /*
> + * calculate start setup count by the rule:
> + * tSU;sto =(8h * p + 1) * T
> + */
> + min_stop_setup_ns = t_input->scl_rise_ns + spec_min_stop_setup_ns;
> + t_output->tsu_sto_count = DIV_ROUND_UP(clk_rate_khz * min_stop_setup_ns
> + - 1000000, 8 * 1000000 * (t_output->div_high));
> +
> + /*
> + * Adjust to the fact that the hardware has an implicit "+1".
> + * NOTE: Above calculations always produce div_low > 0 and div_high > 0.
> + */
> + t_output->div_low -= 1;
> + t_output->div_high -= 1;
> +
> + /* Maximum divider supported by hw is 0xffff */
> + if (t_output->div_low > 0xffff) {
> + t_output->div_low = 0xffff;
> + ret = -EINVAL;
> + }
> +
> + if (t_output->div_high > 0xffff) {
> + t_output->div_high = 0xffff;
> + ret = -EINVAL;
> + }
> +
> + /*
> + * Adjust to the fact that the hardware has an implicit "+1".
> + * NOTE: Above calculations always produce thd_sda_count > 0,
> + * tsu_sta_count > 0 and tsu_sta_count > 0.
> + */
> + t_output->thd_sda_count -= 1;
> + t_output->tsu_sta_count -= 1;
> + t_output->tsu_sto_count -= 1;
> +
> + return ret;
> +}
> +
> static void rk3x_i2c_adapt_div(struct rk3x_i2c *i2c, unsigned long clk_rate)
> {
> u64 t_low_ns, t_high_ns;
> @@ -829,7 +1052,8 @@ static int rk3x_i2c_xfer(struct i2c_adapter *adap,
>
> /* Force a STOP condition without interrupt */
> i2c_writel(i2c, 0, REG_IEN);
> - i2c_writel(i2c, REG_CON_EN | REG_CON_STOP, REG_CON);
> + i2c_writel(i2c, rk3x_i2c_get_con_count(i2c) |
> + REG_CON_EN | REG_CON_STOP, REG_CON);
>
> i2c->state = STATE_IDLE;
>
> @@ -969,7 +1193,9 @@ static int rk3x_i2c_probe(struct platform_device *pdev)
> platform_set_drvdata(pdev, i2c);
>
> version = (readl(i2c->regs + REG_CON) & VERSION_MASK) >> VERSION_SHIFT;
> - if (version == RK3X_I2C_V0)
> + if (version == RK3X_I2C_V1)
> + i2c->ops.calc_clock = rk3x_i2c_v1_calc_clock;
> + else
> i2c->ops.calc_clock = rk3x_i2c_v0_calc_clock;
Perhaps time to use switch-case:
switch ((value & MASK) >> SHIFT) {
case V1:
v1();
break;
case V0:
default:
v0();
break;
}
--
With Best Regards,
Andy Shevchenko
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