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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>
This commit is contained in:
Kyösti Mälkki 2021-04-28 09:13:21 +03:00 committed by Felix Held
parent 5e1c9a9fd6
commit 2263e9b881
1 changed files with 2 additions and 30 deletions
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32
src/drivers/i2c/designware/dw_i2c.c
View File

@ -621,7 +621,6 @@ int dw_i2c_gen_speed_config(uintptr_t dw_i2c_addr,
{ {
const int ic_clk = CONFIG_DRIVERS_I2C_DESIGNWARE_CLOCK_MHZ; const int ic_clk = CONFIG_DRIVERS_I2C_DESIGNWARE_CLOCK_MHZ;
struct dw_i2c_regs *regs; struct dw_i2c_regs *regs;
uint16_t hcnt_min, lcnt_min;
int i; int i;
regs = (struct dw_i2c_regs *)dw_i2c_addr; regs = (struct dw_i2c_regs *)dw_i2c_addr;
@ -637,35 +636,8 @@ int dw_i2c_gen_speed_config(uintptr_t dw_i2c_addr,
return 0; return 0;
} }
/* If rise time is set use the time calculation. */ /* Use the time calculation. */
if (bcfg->rise_time_ns) return dw_i2c_gen_config_rise_fall_time(regs, speed, bcfg, ic_clk, config);
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;
} }
static int dw_i2c_set_speed(unsigned int bus, enum i2c_speed speed, static int dw_i2c_set_speed(unsigned int bus, enum i2c_speed speed,