[coreboot-gerrit] Change in coreboot[master]: drivers/i2c/designware: Use safe defaults for SCL parameters

[Felix Held (Code Review)]

Felix Held has submitted this change. ( https://review.coreboot.org/c/coreboot/+/52723 )

Change subject: drivers/i2c/designware: Use safe defaults for SCL parameters
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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 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52723
Reviewed-by: Tim Wawrzynczak 
Reviewed-by: Furquan Shaikh 
Reviewed-by: Werner Zeh 
Tested-by: build bot (Jenkins) 
---
M src/drivers/i2c/designware/dw_i2c.c
1 file changed, 2 insertions(+), 30 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Werner Zeh: Looks good to me, approved
  Furquan Shaikh: Looks good to me, but someone else must approve
  Tim Wawrzynczak: Looks good to me, approved

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,