linux-kernel - [PATCH 3/4] i2c: uniphier: fix violation of tLOW requirement for Fast-mode

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Message-Id: <1544068528-27657-4-git-send-email-yamada.masahiro@socionext.com>
Date:   Thu,  6 Dec 2018 12:55:27 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     linux-i2c@...r.kernel.org
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/4] i2c: uniphier: fix violation of tLOW requirement for Fast-mode

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@...ionext.com>
---

 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 454f914..c488e55 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);
 }
-- 
2.7.4