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From:   Manikanta Guntupalli <manikanta.guntupalli@xilinx.com>
To:     <michal.simek@xilinx.com>, <michal.simek@amd.com>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-i2c@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
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CC:     Raviteja Narayanam <raviteja.narayanam@xilinx.com>,
        Manikanta Guntupalli <manikanta.guntupalli@xilinx.com>
Subject: [PATCH 03/12] i2c: xiic: Fix Rx and Tx paths in standard mode repeated start
Date:   Fri, 24 Jun 2022 17:35:18 +0530
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From: Raviteja Narayanam <raviteja.narayanam@xilinx.com>

When a combined message request comes from user space, the
controller has to initiate repeated start sequence. In standard
mode, this repeated start sequence is corrupted if there is still
data in the Tx FIFO.

So, always make sure that all the bytes are completely transmitted
out of the FIFO by waiting for TXEMPTY, if the previous message is
of Tx type.

Signed-off-by: Raviteja Narayanam <raviteja.narayanam@xilinx.com>
Signed-off-by: Manikanta Guntupalli <manikanta.guntupalli@xilinx.com>
---
 drivers/i2c/busses/i2c-xiic.c | 54 +++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
index c8b68176427c..2d5214f1ba03 100644
--- a/drivers/i2c/busses/i2c-xiic.c
+++ b/drivers/i2c/busses/i2c-xiic.c
@@ -62,6 +62,7 @@ enum xiic_endian {
  * @singlemaster: Indicates bus is single master
  * @dynamic: Mode of controller
  * @repeated_start: Repeated start operation
+ * @prev_msg_tx: Previous message is Tx
  */
 struct xiic_i2c {
 	struct device *dev;
@@ -80,6 +81,7 @@ struct xiic_i2c {
 	bool singlemaster;
 	bool dynamic;
 	bool repeated_start;
+	bool prev_msg_tx;
 };
 
 #define XIIC_MSB_OFFSET 0
@@ -282,6 +284,24 @@ static int xiic_clear_rx_fifo(struct xiic_i2c *i2c)
 	return 0;
 }
 
+static int xiic_wait_tx_empty(struct xiic_i2c *i2c)
+{
+	u8 isr;
+	unsigned long timeout;
+
+	timeout = jiffies + XIIC_I2C_TIMEOUT;
+	for (isr = xiic_getreg32(i2c, XIIC_IISR_OFFSET);
+		!(isr & XIIC_INTR_TX_EMPTY_MASK);
+			isr = xiic_getreg32(i2c, XIIC_IISR_OFFSET)) {
+		if (time_after(jiffies, timeout)) {
+			dev_err(i2c->dev, "Timeout waiting at Tx empty\n");
+			return -ETIMEDOUT;
+		}
+	}
+
+	return 0;
+}
+
 static int xiic_reinit(struct xiic_i2c *i2c)
 {
 	int ret;
@@ -731,6 +751,20 @@ static void xiic_start_recv(struct xiic_i2c *i2c)
 		xiic_setreg16(i2c, XIIC_DTR_REG_OFFSET, val);
 		local_irq_restore(flags);
 	} else {
+		/*
+		 * If previous message is Tx, make sure that Tx FIFO is empty
+		 * before starting a new transfer as the repeated start in
+		 * standard mode can corrupt the transaction if there are
+		 * still bytes to be transmitted in FIFO
+		 */
+		if (i2c->prev_msg_tx) {
+			int status;
+
+			status = xiic_wait_tx_empty(i2c);
+			if (status)
+				return;
+		}
+
 		cr = xiic_getreg8(i2c, XIIC_CR_REG_OFFSET);
 
 		/* Set Receive fifo depth */
@@ -784,6 +818,8 @@ static void xiic_start_recv(struct xiic_i2c *i2c)
 
 	/* Enable interrupts */
 	xiic_setreg32(i2c, XIIC_DGIER_OFFSET, XIIC_GINTR_ENABLE_MASK);
+
+	i2c->prev_msg_tx = false;
 }
 
 static void xiic_start_send(struct xiic_i2c *i2c)
@@ -820,6 +856,20 @@ static void xiic_start_send(struct xiic_i2c *i2c)
 
 		xiic_fill_tx_fifo(i2c);
 	} else {
+		/*
+		 * If previous message is Tx, make sure that Tx FIFO is empty
+		 * before starting a new transfer as the repeated start in
+		 * standard mode can corrupt the transaction if there are
+		 * still bytes to be transmitted in FIFO
+		 */
+		if (i2c->prev_msg_tx) {
+			int status;
+
+			status = xiic_wait_tx_empty(i2c);
+			if (status)
+				return;
+		}
+
 		/* Check if RSTA should be set */
 		cr = xiic_getreg8(i2c, XIIC_CR_REG_OFFSET);
 		if (cr & XIIC_CR_MSMS_MASK) {
@@ -853,6 +903,7 @@ static void xiic_start_send(struct xiic_i2c *i2c)
 				XIIC_INTR_TX_ERROR_MASK |
 				XIIC_INTR_BNB_MASK);
 	}
+	i2c->prev_msg_tx = true;
 }
 
 static void __xiic_start_xfer(struct xiic_i2c *i2c)
@@ -916,6 +967,9 @@ static int xiic_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 	/* Decide standard mode or Dynamic mode */
 	i2c->dynamic = true;
 
+	/* Initialize prev message type */
+	i2c->prev_msg_tx = false;
+
 	/* Enter standard mode only when read length is > 255 bytes */
 	for (count = 0; count < i2c->nmsgs; count++) {
 		if ((i2c->tx_msg[count].flags & I2C_M_RD) &&
-- 
2.25.1