Commit 47280af8 authored by Wolfram Sang's avatar Wolfram Sang Committed by Wolfram Sang
Browse files

i2c: rcar: calculate divider instead of brute-forcing it 



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: default avatarWolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: default avatarGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: default avatarWolfram Sang <wsa@kernel.org>
parent d7285790

drivers/i2c/busses/i2c-rcar.c

+8 −16
Original line number Diff line number Diff line
@@ -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",