[PATCH v2] i2c: sh_mobile: Switch R-Mobile A1/APE6 and SH-Mobile AG5 to new frequency calculation

[Geert Uytterhoeven <geert+renesas@glider.be>]

Switch the R-Mobile A1, R-Mobile APE6, and SH-Mobile AG5 SoCs to the new
frequency calculation formula, to (a) avoid running the I2C bus too fast,
and (b) bring the low/high ratio closer to the recommended ratio 5/4.

As this makes fast_clock_dt_config and v2_freq_calc_dt_config identical,
merge them into a single fast_clock_dt_config.

Legacy SH users (sh7343, sh7366, and sh772[234]) are left alone, and
still use the old formula.

Measurement results on R-Mobile APE6 and SH-Mobile AG5 (fck=104 MHz,
clks_per_count=2):
  100 kHz: 106 kHz LH=1.12 before, 99.6 kHz L/H=1.22 after
  400 kHz: 384 kHz LH=1.67 before, 392 kHz L/H=1.27 after

Measurement results on R-Mobile A1 (fck=49.5 MHz, clks_per_count=1):
  100 kHz: 106 kHz L/H=1.09 before, 99.6 kHz L/H=1.20 after

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
v2:
  - Merge fast_clock_dt_config and v2_freq_calc_dt_config,
  - Document that legacy SH users are untouched.
---
 drivers/i2c/busses/i2c-sh_mobile.c | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/drivers/i2c/busses/i2c-sh_mobile.c b/drivers/i2c/busses/i2c-sh_mobile.c
index 5adbe62cf6212865..c65ac3d7eadc5b58 100644
--- a/drivers/i2c/busses/i2c-sh_mobile.c
+++ b/drivers/i2c/busses/i2c-sh_mobile.c
@@ -773,7 +773,7 @@ static int sh_mobile_i2c_r8a7740_workaround(struct sh_mobile_i2c_data *pd)
 	iic_wr(pd, ICCR, ICCR_TRS);
 	udelay(10);
 
-	return sh_mobile_i2c_init(pd);
+	return sh_mobile_i2c_v2_init(pd);
 }
 
 static const struct sh_mobile_dt_config default_dt_config = {
@@ -782,11 +782,6 @@ static const struct sh_mobile_dt_config default_dt_config = {
 };
 
 static const struct sh_mobile_dt_config fast_clock_dt_config = {
-	.clks_per_count = 2,
-	.setup = sh_mobile_i2c_init,
-};
-
-static const struct sh_mobile_dt_config v2_freq_calc_dt_config = {
 	.clks_per_count = 2,
 	.setup = sh_mobile_i2c_v2_init,
 };
@@ -799,17 +794,17 @@ static const struct sh_mobile_dt_config r8a7740_dt_config = {
 static const struct of_device_id sh_mobile_i2c_dt_ids[] = {
 	{ .compatible = "renesas,iic-r8a73a4", .data = &fast_clock_dt_config },
 	{ .compatible = "renesas,iic-r8a7740", .data = &r8a7740_dt_config },
-	{ .compatible = "renesas,iic-r8a774c0", .data = &v2_freq_calc_dt_config },
-	{ .compatible = "renesas,iic-r8a7790", .data = &v2_freq_calc_dt_config },
-	{ .compatible = "renesas,iic-r8a7791", .data = &v2_freq_calc_dt_config },
-	{ .compatible = "renesas,iic-r8a7792", .data = &v2_freq_calc_dt_config },
-	{ .compatible = "renesas,iic-r8a7793", .data = &v2_freq_calc_dt_config },
-	{ .compatible = "renesas,iic-r8a7794", .data = &v2_freq_calc_dt_config },
-	{ .compatible = "renesas,iic-r8a7795", .data = &v2_freq_calc_dt_config },
-	{ .compatible = "renesas,iic-r8a77990", .data = &v2_freq_calc_dt_config },
+	{ .compatible = "renesas,iic-r8a774c0", .data = &fast_clock_dt_config },
+	{ .compatible = "renesas,iic-r8a7790", .data = &fast_clock_dt_config },
+	{ .compatible = "renesas,iic-r8a7791", .data = &fast_clock_dt_config },
+	{ .compatible = "renesas,iic-r8a7792", .data = &fast_clock_dt_config },
+	{ .compatible = "renesas,iic-r8a7793", .data = &fast_clock_dt_config },
+	{ .compatible = "renesas,iic-r8a7794", .data = &fast_clock_dt_config },
+	{ .compatible = "renesas,iic-r8a7795", .data = &fast_clock_dt_config },
+	{ .compatible = "renesas,iic-r8a77990", .data = &fast_clock_dt_config },
 	{ .compatible = "renesas,iic-sh73a0", .data = &fast_clock_dt_config },
-	{ .compatible = "renesas,rcar-gen2-iic", .data = &v2_freq_calc_dt_config },
-	{ .compatible = "renesas,rcar-gen3-iic", .data = &v2_freq_calc_dt_config },
+	{ .compatible = "renesas,rcar-gen2-iic", .data = &fast_clock_dt_config },
+	{ .compatible = "renesas,rcar-gen3-iic", .data = &fast_clock_dt_config },
 	{ .compatible = "renesas,rmobile-iic", .data = &default_dt_config },
 	{},
 };
-- 
2.34.1