linux-kernel - [PATCH 2/3] i2c:imx: Add an extra read at the end of an I2C slave read

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Date:   Mon,  4 Oct 2021 19:32:15 -0500
From:   minyard@....org
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Pengutronix Kernel Team <kernel@...gutronix.de>,
        linux-i2c@...r.kernel.org,
        Andrew Manley <andrew.manley@...lingtech.com>,
        linux-kernel@...r.kernel.org, Corey Minyard <cminyard@...sta.com>,
        Corey Minyard <minyard@....org>
Subject: [PATCH 2/3] i2c:imx: Add an extra read at the end of an I2C slave read

From: Corey Minyard <cminyard@...sta.com>

The I2C slave interface expects that the driver will read ahead one
byte.  The IMX driver/device doesn't do this, but simulate it so that
read operations get their index set correctly.

Signed-off-by: Corey Minyard <minyard@....org>
Tested-by: Andrew Manley <andrew.manley@...lingtech.com>
Reviewed-by: Andrew Manley <andrew.manley@...lingtech.com>
---
 drivers/i2c/busses/i2c-imx.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index 97369fe48b30..26a04dc0590b 100644
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -769,6 +769,15 @@ static irqreturn_t i2c_imx_slave_handle(struct imx_i2c_struct *i2c_imx,
 		ctl &= ~I2CR_MTX;
 		imx_i2c_write_reg(ctl, i2c_imx, IMX_I2C_I2CR);
 		imx_i2c_read_reg(i2c_imx, IMX_I2C_I2DR);
+
+		/*
+		 * The i2c slave interface requires one extra dummy
+		 * read at the end to keep things in line.  See the
+		 * I2C slave docs for details.
+		 */
+		i2c_imx_slave_event(i2c_imx,
+				    I2C_SLAVE_READ_PROCESSED, &value);
+
 		i2c_imx_slave_finish_op(i2c_imx);
 		return IRQ_HANDLED;
 	}
-- 
2.25.1