drivers/i2c/designware: Use safe defaults for SCL parameters
Inspired by discussion in CB:22822.
If I2C bus step response has not been measured, assume the layout to
have been designed with a minimal capacitance and SCL rise and fall
times of 0 ns. The calculations will add the required amount of
reference clocks for the host to drive SCL high or low, such that the
maximum bus frequency specification is met.
Change-Id: Icbafae22c83ffbc16c179fb5412fb4fd6b70813a
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52723
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/drivers/i2c/designware/dw_i2c.c b/src/drivers/i2c/designware/dw_i2c.c
index c0212c3..2e2d20d 100644
--- a/src/drivers/i2c/designware/dw_i2c.c
+++ b/src/drivers/i2c/designware/dw_i2c.c
@@ -621,7 +621,6 @@
{
const int ic_clk = CONFIG_DRIVERS_I2C_DESIGNWARE_CLOCK_MHZ;
struct dw_i2c_regs *regs;
- uint16_t hcnt_min, lcnt_min;
int i;
regs = (struct dw_i2c_regs *)dw_i2c_addr;
@@ -637,35 +636,8 @@
return 0;
}
- /* If rise time is set use the time calculation. */
- if (bcfg->rise_time_ns)
- return dw_i2c_gen_config_rise_fall_time(regs, speed, bcfg,
- ic_clk, config);
-
- if (speed >= I2C_SPEED_HIGH) {
- /* High speed */
- hcnt_min = MIN_HS_SCL_HIGHTIME;
- lcnt_min = MIN_HS_SCL_LOWTIME;
- } else if (speed >= I2C_SPEED_FAST_PLUS) {
- /* Fast-Plus speed */
- hcnt_min = MIN_FP_SCL_HIGHTIME;
- lcnt_min = MIN_FP_SCL_LOWTIME;
- } else if (speed >= I2C_SPEED_FAST) {
- /* Fast speed */
- hcnt_min = MIN_FS_SCL_HIGHTIME;
- lcnt_min = MIN_FS_SCL_LOWTIME;
- } else {
- /* Standard speed */
- hcnt_min = MIN_SS_SCL_HIGHTIME;
- lcnt_min = MIN_SS_SCL_LOWTIME;
- }
-
- config->speed = speed;
- config->scl_hcnt = ic_clk * hcnt_min / KHz;
- config->scl_lcnt = ic_clk * lcnt_min / KHz;
- config->sda_hold = ic_clk * DEFAULT_SDA_HOLD_TIME / KHz;
-
- return 0;
+ /* Use the time calculation. */
+ return dw_i2c_gen_config_rise_fall_time(regs, speed, bcfg, ic_clk, config);
}
static int dw_i2c_set_speed(unsigned int bus, enum i2c_speed speed,