i2c: riic: Always round-up when calculating bus period

commit de6b43798d9043a7c749a0428dbb02d5fff156e5 upstream.

Currently, the RIIC driver may run the I2C bus faster than requested,
which may cause subtle failures.  E.g. Biju reported a measured bus
speed of 450 kHz instead of the expected maximum of 400 kHz on RZ/G2L.

The initial calculation of the bus period uses DIV_ROUND_UP(), to make
sure the actual bus speed never becomes faster than the requested bus
speed.  However, the subsequent division-by-two steps do not use
round-up, which may lead to a too-small period, hence a too-fast and
possible out-of-spec bus speed.  E.g. on RZ/Five, requesting a bus speed
of 100 resp. 400 kHz will yield too-fast target bus speeds of 100806
resp. 403226 Hz instead of 97656 resp. 390625 Hz.

Fix this by using DIV_ROUND_UP() in the subsequent divisions, too.

Tested on RZ/A1H, RZ/A2M, and RZ/Five.

Fixes: d982d66514192cdb ("i2c: riic: remove clock and frequency restrictions")
Reported-by: Biju Das <biju.das.jz@bp.renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: <stable@vger.kernel.org> # v4.15+
Link: https://lore.kernel.org/r/c59aea77998dfea1b4456c4b33b55ab216fcbf5e.1732284746.git.geert+renesas@glider.be
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/i2c/busses/i2c-riic.c

@@ -323,7 +323,7 @@ static int riic_init_hw(struct riic_dev *riic, struct i2c_timings *t)
 		if (brl <= (0x1F + 3))
 			break;
 
-		total_ticks /= 2;
+		total_ticks = DIV_ROUND_UP(total_ticks, 2);
 		rate /= 2;
 	}