spi/spi-xilinx: Fix spurious IRQ ACK on irq mode

commit 74346841 upstream.

The ACK of an inexistent IRQ can trigger an spurious IRQ that breaks the
txrx logic. This has been observed on axi_quad_spi:3.2 core.

This patch only ACKs IRQs that have not been Acknowledge jet.
Reported-by: Edward Kigwana <ekigwana@scires.com>
Tested-by: Edward Kigwana <ekigwana@scires.com>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/spi/spi-xilinx.c

@@ -249,19 +249,23 @@ static int xilinx_spi_txrx_bufs(struct spi_device *spi, struct spi_transfer *t)
 	xspi->tx_ptr = t->tx_buf;
 	xspi->rx_ptr = t->rx_buf;
 	remaining_words = t->len / xspi->bytes_per_word;
-	reinit_completion(&xspi->done);
 
 	if (xspi->irq >= 0 &&  remaining_words > xspi->buffer_size) {
+		u32 isr;
 		use_irq = true;
-		xspi->write_fn(XSPI_INTR_TX_EMPTY,
-				xspi->regs + XIPIF_V123B_IISR_OFFSET);
-		/* Enable the global IPIF interrupt */
-		xspi->write_fn(XIPIF_V123B_GINTR_ENABLE,
-				xspi->regs + XIPIF_V123B_DGIER_OFFSET);
 		/* Inhibit irq to avoid spurious irqs on tx_empty*/
 		cr = xspi->read_fn(xspi->regs + XSPI_CR_OFFSET);
 		xspi->write_fn(cr | XSPI_CR_TRANS_INHIBIT,
 			       xspi->regs + XSPI_CR_OFFSET);
+		/* ACK old irqs (if any) */
+		isr = xspi->read_fn(xspi->regs + XIPIF_V123B_IISR_OFFSET);
+		if (isr)
+			xspi->write_fn(isr,
+				       xspi->regs + XIPIF_V123B_IISR_OFFSET);
+		/* Enable the global IPIF interrupt */
+		xspi->write_fn(XIPIF_V123B_GINTR_ENABLE,
+				xspi->regs + XIPIF_V123B_DGIER_OFFSET);
+		reinit_completion(&xspi->done);
 	}
 
 	while (remaining_words) {