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.
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@xxxxxxxxx>
---
Measurements after applying "[PATCH 1/3] ARM: dts: renesas: r8a73a4: Fix
external clocks and clock rate"[1]. Before, the clock rates were even
4% higher.
Notes:
- fast_clock_dt_config is now unused, so I guess we should drop it,
and rename v2_freq_calc_dt_config to fast_clock_dt_config?
- The formulas in the documentation for R-Mobile A1 do not include the
"-1" and "-5", presumably this is for rounding?
- The formulas in the documentation for SH-Mobile AG5 include
the "-1" and "-5" in the example for 400 kHz, but not in the example
for 100 kHz.
- The SH-Mobile AG5 documentation suggests to use an L/H ratio of 5/3
instead of 5/4 for 400 kHz, which means the old formula is better
for 400 kHz?
- Remaining users of the old formula are sh7343, sh7366, and sh772[234].
At least for sh772[234], the "Transfer Rate" formula in the
documentation is the same as for R-Mobile A1. Hence probably we
should switch the default_dt_config and the default fallback to the
"v2" formula, too?
- I am still a bit puzzled, as the "v2" formula introduced in commit
4ecfb9d3b229fff5 ("i2c: sh_mobile: add new frequency calculation for
later SoC") is basically what the driver did before commit
23a612916a51cc37 ("i2c: i2c-sh_mobile: optimize ICCH/ICCL values
according to I2C bus speed")?
[1] https://lore.kernel.org/r/1692bc8cd465d62168cbf110522ad62a7af3f606.1705315614.git.geert+renesas@xxxxxxxxx
---
drivers/i2c/busses/i2c-sh_mobile.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/i2c/busses/i2c-sh_mobile.c b/drivers/i2c/busses/i2c-sh_mobile.c
index 5adbe62cf6212865..9e2e12d482d8e640 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 = {
@@ -797,7 +797,7 @@ 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-r8a73a4", .data = &v2_freq_calc_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 },
@@ -807,7 +807,7 @@ static const struct of_device_id sh_mobile_i2c_dt_ids[] = {
{ .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-sh73a0", .data = &fast_clock_dt_config },
+ { .compatible = "renesas,iic-sh73a0", .data = &v2_freq_calc_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,rmobile-iic", .data = &default_dt_config },
--
2.34.1
