diff options
Diffstat (limited to 'drivers/i2c/busses/i2c-rk3x.c')
| -rw-r--r-- | drivers/i2c/busses/i2c-rk3x.c | 99 |
1 files changed, 75 insertions, 24 deletions
diff --git a/drivers/i2c/busses/i2c-rk3x.c b/drivers/i2c/busses/i2c-rk3x.c index 9246284..5f96b1b 100644 --- a/drivers/i2c/busses/i2c-rk3x.c +++ b/drivers/i2c/busses/i2c-rk3x.c @@ -102,6 +102,9 @@ struct rk3x_i2c { /* Settings */ unsigned int scl_frequency; + unsigned int scl_rise_ns; + unsigned int scl_fall_ns; + unsigned int sda_fall_ns; /* Synchronization & notification */ spinlock_t lock; @@ -435,6 +438,9 @@ out: * * @clk_rate: I2C input clock rate * @scl_rate: Desired SCL rate + * @scl_rise_ns: How many ns it takes for SCL to rise. + * @scl_fall_ns: How many ns it takes for SCL to fall. + * @sda_fall_ns: How many ns it takes for SDA to fall. * @div_low: Divider output for low * @div_high: Divider output for high * @@ -443,11 +449,16 @@ out: * too high, we silently use the highest possible rate. */ static int rk3x_i2c_calc_divs(unsigned long clk_rate, unsigned long scl_rate, + unsigned long scl_rise_ns, + unsigned long scl_fall_ns, + unsigned long sda_fall_ns, unsigned long *div_low, unsigned long *div_high) { - unsigned long min_low_ns, min_high_ns; - unsigned long max_data_hold_ns; + unsigned long spec_min_low_ns, spec_min_high_ns; + unsigned long spec_setup_start, spec_max_data_hold_ns; unsigned long data_hold_buffer_ns; + + unsigned long min_low_ns, min_high_ns; unsigned long max_low_ns, min_total_ns; unsigned long clk_rate_khz, scl_rate_khz; @@ -469,29 +480,50 @@ static int rk3x_i2c_calc_divs(unsigned long clk_rate, unsigned long scl_rate, 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 + * 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. + * max_low_ns: The maximum number of ns we can hold low to meet + * I2C specification. * - * Note: max_low_ns should be (max data hold time * 2 - buffer) + * Note: max_low_ns should be (maximum 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 <= 100000) { - min_low_ns = 4700; - min_high_ns = 4000; - max_data_hold_ns = 3450; + /* Standard-mode */ + spec_min_low_ns = 4700; + spec_setup_start = 4700; + spec_min_high_ns = 4000; + spec_max_data_hold_ns = 3450; data_hold_buffer_ns = 50; } else { - min_low_ns = 1300; - min_high_ns = 600; - max_data_hold_ns = 900; + /* Fast-mode */ + spec_min_low_ns = 1300; + spec_setup_start = 600; + spec_min_high_ns = 600; + spec_max_data_hold_ns = 900; data_hold_buffer_ns = 50; } - max_low_ns = max_data_hold_ns * 2 - data_hold_buffer_ns; + min_high_ns = scl_rise_ns + spec_min_high_ns; + + /* + * Timings for repeated start: + * - controller appears to drop SDA at .875x (7/8) programmed clk high. + * - controller appears to keep SCL high for 2x programmed clk high. + * + * We need to account for those rules in picking our "high" time so + * we meet tSU;STA and tHD;STA times. + */ + min_high_ns = max(min_high_ns, + DIV_ROUND_UP((scl_rise_ns + spec_setup_start) * 1000, 875)); + min_high_ns = max(min_high_ns, + DIV_ROUND_UP((scl_rise_ns + spec_setup_start + + sda_fall_ns + spec_min_high_ns), 2)); + + min_low_ns = scl_fall_ns + spec_min_low_ns; + max_low_ns = spec_max_data_hold_ns * 2 - data_hold_buffer_ns; min_total_ns = min_low_ns + min_high_ns; /* Adjust to avoid overflow */ @@ -510,8 +542,8 @@ static int rk3x_i2c_calc_divs(unsigned long clk_rate, unsigned long scl_rate, 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. + * 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. */ max_low_div = clk_rate_khz * max_low_ns / (8 * 1000000); @@ -544,7 +576,7 @@ static int rk3x_i2c_calc_divs(unsigned long clk_rate, unsigned long scl_rate, ideal_low_div = DIV_ROUND_UP(clk_rate_khz * min_low_ns, scl_rate_khz * 8 * min_total_ns); - /* Don't allow it to go over the max */ + /* Don't allow it to go over the maximum */ if (ideal_low_div > max_low_div) ideal_low_div = max_low_div; @@ -588,9 +620,9 @@ static void rk3x_i2c_adapt_div(struct rk3x_i2c *i2c, unsigned long clk_rate) u64 t_low_ns, t_high_ns; int ret; - ret = rk3x_i2c_calc_divs(clk_rate, i2c->scl_frequency, &div_low, - &div_high); - + ret = rk3x_i2c_calc_divs(clk_rate, i2c->scl_frequency, i2c->scl_rise_ns, + i2c->scl_fall_ns, i2c->sda_fall_ns, + &div_low, &div_high); WARN_ONCE(ret != 0, "Could not reach SCL freq %u", i2c->scl_frequency); clk_enable(i2c->clk); @@ -633,9 +665,10 @@ static int rk3x_i2c_clk_notifier_cb(struct notifier_block *nb, unsigned long switch (event) { case PRE_RATE_CHANGE: if (rk3x_i2c_calc_divs(ndata->new_rate, i2c->scl_frequency, - &div_low, &div_high) != 0) { + i2c->scl_rise_ns, i2c->scl_fall_ns, + i2c->sda_fall_ns, + &div_low, &div_high) != 0) return NOTIFY_STOP; - } /* scale up */ if (ndata->new_rate > ndata->old_rate) @@ -859,6 +892,24 @@ static int rk3x_i2c_probe(struct platform_device *pdev) i2c->scl_frequency = DEFAULT_SCL_RATE; } + /* + * Read rise and fall time from device tree. If not available use + * the default maximum timing from the specification. + */ + if (of_property_read_u32(pdev->dev.of_node, "i2c-scl-rising-time-ns", + &i2c->scl_rise_ns)) { + if (i2c->scl_frequency <= 100000) + i2c->scl_rise_ns = 1000; + else + i2c->scl_rise_ns = 300; + } + if (of_property_read_u32(pdev->dev.of_node, "i2c-scl-falling-time-ns", + &i2c->scl_fall_ns)) + i2c->scl_fall_ns = 300; + if (of_property_read_u32(pdev->dev.of_node, "i2c-sda-falling-time-ns", + &i2c->scl_fall_ns)) + i2c->sda_fall_ns = i2c->scl_fall_ns; + strlcpy(i2c->adap.name, "rk3x-i2c", sizeof(i2c->adap.name)); i2c->adap.owner = THIS_MODULE; i2c->adap.algo = &rk3x_i2c_algorithm; |
