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

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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>
This commit is contained in:
Masahiro Yamada 2018-12-06 12:55:27 +09:00 committed by Wolfram Sang
parent cd8843f541
commit 8469636ab5
1 changed files with 7 additions and 1 deletions
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8
drivers/i2c/busses/i2c-uniphier.c
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@ -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);
}