linux-kernel - [PATCH 3.16 222/328] i2c: xiic: Make the start and the byte count write atomic

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Message-ID: <lsq.1544392233.506931919@decadent.org.uk>
Date:   Sun, 09 Dec 2018 21:50:33 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Shubhrajyoti Datta" <shubhrajyoti.datta@...inx.com>,
        "Wolfram Sang" <wsa@...-dreams.de>,
        "Michal Simek" <michal.simek@...inx.com>
Subject: [PATCH 3.16 222/328] i2c: xiic: Make the start and the byte count
 write atomic

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Shubhrajyoti Datta <shubhrajyoti.datta@...inx.com>

commit ae7304c3ea28a3ba47a7a8312c76c654ef24967e upstream.

Disable interrupts while configuring the transfer and enable them back.

We have below as the programming sequence
1. start and slave address
2. byte count and stop

In some customer platform there was a lot of interrupts between 1 and 2
and after slave address (around 7 clock cyles) if 2 is not executed
then the transaction is nacked.

To fix this case make the 2 writes atomic.

Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@...inx.com>
Signed-off-by: Michal Simek <michal.simek@...inx.com>
[wsa: added a newline for better readability]
Signed-off-by: Wolfram Sang <wsa@...-dreams.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/i2c/busses/i2c-xiic.c | 4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/i2c/busses/i2c-xiic.c
+++ b/drivers/i2c/busses/i2c-xiic.c
@@ -504,6 +504,7 @@ static void xiic_start_recv(struct xiic_
 {
 	u8 rx_watermark;
 	struct i2c_msg *msg = i2c->rx_msg = i2c->tx_msg;
+	unsigned long flags;
 
 	/* Clear and enable Rx full interrupt. */
 	xiic_irq_clr_en(i2c, XIIC_INTR_RX_FULL_MASK | XIIC_INTR_TX_ERROR_MASK);
@@ -519,6 +520,7 @@ static void xiic_start_recv(struct xiic_
 		rx_watermark = IIC_RX_FIFO_DEPTH;
 	xiic_setreg8(i2c, XIIC_RFD_REG_OFFSET, rx_watermark - 1);
 
+	local_irq_save(flags);
 	if (!(msg->flags & I2C_M_NOSTART))
 		/* write the address */
 		xiic_setreg16(i2c, XIIC_DTR_REG_OFFSET,
@@ -529,6 +531,8 @@ static void xiic_start_recv(struct xiic_
 
 	xiic_setreg16(i2c, XIIC_DTR_REG_OFFSET,
 		msg->len | ((i2c->nmsgs == 1) ? XIIC_TX_DYN_STOP_MASK : 0));
+	local_irq_restore(flags);
+
 	if (i2c->nmsgs == 1)
 		/* very last, enable bus not busy as well */
 		xiic_irq_clr_en(i2c, XIIC_INTR_BNB_MASK);