5.4-stable review patch. If anyone has any objections, please let me know.
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From: Geert Uytterhoeven geert+renesas@glider.be
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.173228474... Signed-off-by: Andi Shyti andi.shyti@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/i2c/busses/i2c-riic.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/i2c/busses/i2c-riic.c +++ b/drivers/i2c/busses/i2c-riic.c @@ -323,7 +323,7 @@ static int riic_init_hw(struct riic_dev if (brl <= (0x1F + 3)) break;
- total_ticks /= 2; + total_ticks = DIV_ROUND_UP(total_ticks, 2); rate /= 2; }