From de6b43798d9043a7c749a0428dbb02d5fff156e5 Mon Sep 17 00:00:00 2001 From: Geert Uytterhoeven Date: Fri, 22 Nov 2024 15:14:35 +0100 Subject: [PATCH] i2c: riic: Always round-up when calculating bus period 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 Signed-off-by: Geert Uytterhoeven Cc: # v4.15+ Link: https://lore.kernel.org/r/c59aea77998dfea1b4456c4b33b55ab216fcbf5e.1732284746.git.geert+renesas@glider.be Signed-off-by: Andi Shyti --- drivers/i2c/busses/i2c-riic.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/i2c/busses/i2c-riic.c b/drivers/i2c/busses/i2c-riic.c index c218f73c3650..9264adc97ca9 100644 --- a/drivers/i2c/busses/i2c-riic.c +++ b/drivers/i2c/busses/i2c-riic.c @@ -352,7 +352,7 @@ static int riic_init_hw(struct riic_dev *riic) if (brl <= (0x1F + 3)) break; - total_ticks /= 2; + total_ticks = DIV_ROUND_UP(total_ticks, 2); rate /= 2; } -- 2.25.1