linux-kernel - [PATCH 4.19 64/67] i2c: uniphier-f: fix violation of tLOW requirement for Fast-mode

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Date:   Thu, 20 Dec 2018 10:19:16 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 64/67] i2c: uniphier-f: fix violation of tLOW requirement for Fast-mode

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@...ionext.com>
Signed-off-by: Wolfram Sang <wsa@...-dreams.de>
Signed-off-by: Sasha Levin <sashal@...nel.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