Instead of trying all values, we can actually compute it as the comment
suggests. It is unclear what the comment means with "involved", it works
nicely.
Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
---
@Geert: I hope the formulas are more clear now?
@Andi: I don't think that replacing 0x3f with a define helps
understanding the code, but I am open for discussion.
drivers/i2c/busses/i2c-rcar.c | 24 ++++++++----------------
1 file changed, 8 insertions(+), 16 deletions(-)
diff --git a/drivers/i2c/busses/i2c-rcar.c b/drivers/i2c/busses/i2c-rcar.c
index 4bf47e35094f..2585092bed52 100644
--- a/drivers/i2c/busses/i2c-rcar.c
+++ b/drivers/i2c/busses/i2c-rcar.c
@@ -303,24 +303,16 @@ static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv)
round = (round + 500) / 1000;
/*
- * SCL = ick / (20 + SCGD * 8 + F[(ticf + tr + intd) * ick])
- *
- * Calculation result (= SCL) should be less than
- * bus_speed for hardware safety
- *
- * We could use something along the lines of
- * div = ick / (bus_speed + 1) + 1;
- * scgd = (div - 20 - round + 7) / 8;
- * scl = ick / (20 + (scgd * 8) + round);
- * (not fully verified) but that would get pretty involved
+ * SCL = ick / (20 + 8 * SCGD + F[(ticf + tr + intd) * ick])
+ * 20 + 8 * SCGD + F[...] = ick / SCL
+ * SCGD = ((ick / SCL) - 20 - F[...]) / 8
+ * Result (= SCL) should be less than bus_speed for hardware safety
*/
- for (scgd = 0; scgd < 0x40; scgd++) {
- scl = ick / (20 + (scgd * 8) + round);
- if (scl <= t.bus_freq_hz)
- break;
- }
+ scgd = DIV_ROUND_UP(ick, t.bus_freq_hz ?: 1);
+ scgd = DIV_ROUND_UP(scgd - 20 - round, 8);
+ scl = ick / (20 + 8 * scgd + round);
- if (scgd == 0x40)
+ if (scgd > 0x3f)
goto err_no_val;
dev_dbg(dev, "clk %u/%u(%lu), round %u, CDF: %u, SCGD: %u\n",
--
2.35.1
