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Subject[PATCH 4.19 64/67] i2c: uniphier-f: fix violation of tLOW requirement for Fast-mode
Date
4.19-stable review patch.  If anyone has any objections, please let me know.

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

[ Upstream commit ece27a337d42a3197935711997f2880f0957ed7e ]

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-f.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-uniphier-f.c b/drivers/i2c/busses/i2c-uniphier-f.c
index a403e8579b65..bc26ec822e26 100644
--- a/drivers/i2c/busses/i2c-uniphier-f.c
+++ b/drivers/i2c/busses/i2c-uniphier-f.c
@@ -470,9 +470,26 @@ static void uniphier_fi2c_hw_init(struct uniphier_fi2c_priv *priv)

uniphier_fi2c_reset(priv);

+ /*
+ * Standard-mode: tLOW + tHIGH = 10 us
+ * Fast-mode: tLOW + tHIGH = 2.5 us
+ */
writel(cyc, priv->membase + UNIPHIER_FI2C_CYC);
- writel(cyc / 2, priv->membase + UNIPHIER_FI2C_LCTL);
+ /*
+ * Standard-mode: tLOW = 4.7 us, tHIGH = 4.0 us, tBUF = 4.7 us
+ * Fast-mode: tLOW = 1.3 us, tHIGH = 0.6 us, tBUF = 1.3 us
+ * "tLow/tHIGH = 5/4" meets both.
+ */
+ writel(cyc * 5 / 9, priv->membase + UNIPHIER_FI2C_LCTL);
+ /*
+ * Standard-mode: tHD;STA = 4.0 us, tSU;STA = 4.7 us, tSU;STO = 4.0 us
+ * Fast-mode: tHD;STA = 0.6 us, tSU;STA = 0.6 us, tSU;STO = 0.6 us
+ */
writel(cyc / 2, priv->membase + UNIPHIER_FI2C_SSUT);
+ /*
+ * Standard-mode: tSU;DAT = 250 ns
+ * Fast-mode: tSU;DAT = 100 ns
+ */
writel(cyc / 16, priv->membase + UNIPHIER_FI2C_DSUT);

uniphier_fi2c_prepare_operation(priv);
--
2.19.1


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