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Subject[PATCH 4.14 68/72] i2c: uniphier: fix violation of tLOW requirement for Fast-mode
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 8469636ab5d8c77645b953746c10fda6983a8830 ]

Currently, the clock duty is set as tLOW/tHIGH = 1/1. For Fast-mode,
tLOW is set to 1.25 us while the I2C spec requires tLOW >= 1.3 us.

tLOW/tHIGH = 5/4 would meet both Standard-mode and Fast-mode:
Standard-mode: tLOW = 5.56 us, tHIGH = 4.44 us
Fast-mode: tLOW = 1.39 us, tHIGH = 1.11 us

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/i2c/busses/i2c-uniphier.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-uniphier.c b/drivers/i2c/busses/i2c-uniphier.c
index 454f914ae66d..c488e558aef7 100644
--- a/drivers/i2c/busses/i2c-uniphier.c
+++ b/drivers/i2c/busses/i2c-uniphier.c
@@ -320,7 +320,13 @@ static void uniphier_i2c_hw_init(struct uniphier_i2c_priv *priv)

uniphier_i2c_reset(priv, true);

- writel((cyc / 2 << 16) | cyc, priv->membase + UNIPHIER_I2C_CLK);
+ /*
+ * Bit30-16: clock cycles of tLOW.
+ * Standard-mode: tLOW = 4.7 us, tHIGH = 4.0 us
+ * Fast-mode: tLOW = 1.3 us, tHIGH = 0.6 us
+ * "tLow/tHIGH = 5/4" meets both.
+ */
+ writel((cyc * 5 / 9 << 16) | cyc, priv->membase + UNIPHIER_I2C_CLK);

uniphier_i2c_reset(priv, false);
}
--
2.19.1


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