i2c: uniphier: fix violation of tLOW requirement for Fast-mode

[ 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>

diff --git a/drivers/i2c/busses/i2c-uniphier.c b/drivers/i2c/busses/i2c-uniphier.c
index 454f914..c488e55 100644 (file)
--- 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);
 }