i2c: xiic: Make the start and the byte count write atomic

BugLink: https://bugs.launchpad.net/bugs/1798539

commit ae7304c3 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@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
[wsa: added a newline for better readability]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/i2c/busses/i2c-xiic.c

@@ -533,6 +533,7 @@ static void xiic_start_recv(struct xiic_i2c *i2c)
 {
 	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);
@@ -548,6 +549,7 @@ static void xiic_start_recv(struct xiic_i2c *i2c)
 		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,
@@ -558,6 +560,8 @@ static void xiic_start_recv(struct xiic_i2c *i2c)
 
 	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);