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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Fabrice Gasnier <fabrice.gasnier@st.com>,
        Pierre-Yves MORDRET <pierre-yves.mordret@st.com>,
        Wolfram Sang <wsa@the-dreams.de>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.19 31/79] i2c: stm32f7: fix first byte to send in slave mode
Date:   Fri,  8 Nov 2019 19:50:11 +0100
Message-Id: <20191108174802.672637977@linuxfoundation.org>
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From: Fabrice Gasnier <fabrice.gasnier@st.com>

[ Upstream commit 02e64276c6dbcc4c5f39844f33d18180832a58f3 ]

The slave-interface documentation [1] states "the bus driver should
transmit the first byte" upon I2C_SLAVE_READ_REQUESTED slave event:
- 'val': backend returns first byte to be sent
The driver currently ignores the 1st byte to send on this event.

[1] https://www.kernel.org/doc/Documentation/i2c/slave-interface

Fixes: 60d609f30de2 ("i2c: i2c-stm32f7: Add slave support")
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Reviewed-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/i2c/busses/i2c-stm32f7.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/i2c/busses/i2c-stm32f7.c b/drivers/i2c/busses/i2c-stm32f7.c
index ac9c9486b834c..48521bc8a4d23 100644
--- a/drivers/i2c/busses/i2c-stm32f7.c
+++ b/drivers/i2c/busses/i2c-stm32f7.c
@@ -1177,6 +1177,8 @@ static void stm32f7_i2c_slave_start(struct stm32f7_i2c_dev *i2c_dev)
 			STM32F7_I2C_CR1_TXIE;
 		stm32f7_i2c_set_bits(base + STM32F7_I2C_CR1, mask);
 
+		/* Write 1st data byte */
+		writel_relaxed(value, base + STM32F7_I2C_TXDR);
 	} else {
 		/* Notify i2c slave that new write transfer is starting */
 		i2c_slave_event(slave, I2C_SLAVE_WRITE_REQUESTED, &value);
-- 
2.20.1