spi: rspi: avoid uninitialized variable access

The newly introduced rspi_pio_transfer_in_or_our() function must
take either a valid 'rx' or 'tx' pointer, and has undefined behavior
if both are NULL, as found by 'gcc -Wmaybe-unintialized':

drivers/spi/spi-rspi.c: In function 'rspi_pio_transfer_in_or_our':
drivers/spi/spi-rspi.c:558:5: error: 'len' may be used uninitialized in this function [-Werror=maybe-uninitialized]

The analysis of the function is correct in principle, but the code
is currently safe because both callers always pass exactly one
of the two pointers.

Looking closer at this function shows that having a combined
method for rx and tx here actually increases the complexity
and the size of the file. This simplifies it again by keeping
the two separate, which then ends up avoiding that warning.

Fixes: 3be09bec42a8 ("spi: rspi: supports 32bytes buffer for DUAL and QUAD")
Signed-off-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-rspi.c

···
 	return 0;
 }
 
-static int rspi_pio_transfer_in_or_our(struct rspi_data *rspi, const u8 *tx,
-				       u8 *rx, unsigned int n)
-{
-	unsigned int i, len;
-	int ret;
-
-	while (n > 0) {
-		if (tx) {
-			len = qspi_set_send_trigger(rspi, n);
-			if (len == QSPI_BUFFER_SIZE) {
-				ret = rspi_wait_for_tx_empty(rspi);
-				if (ret < 0) {
-					dev_err(&rspi->master->dev, "transmit timeout\n");
-					return ret;
-				}
-				for (i = 0; i < len; i++)
-					rspi_write_data(rspi, *tx++);
-			} else {
-				ret = rspi_pio_transfer(rspi, tx, NULL, n);
-				if (ret < 0)
-					return ret;
-			}
-		}
-		if (rx) {
-			len = qspi_set_receive_trigger(rspi, n);
-			if (len == QSPI_BUFFER_SIZE) {
-				ret = rspi_wait_for_rx_full(rspi);
-				if (ret < 0) {
-					dev_err(&rspi->master->dev, "receive timeout\n");
-					return ret;
-				}
-				for (i = 0; i < len; i++)
-					*rx++ = rspi_read_data(rspi);
-			} else {
-				ret = rspi_pio_transfer(rspi, NULL, rx, n);
-				if (ret < 0)
-					return ret;
-				*rx++ = ret;
-			}
-		}
-		n -= len;
-	}
-	return 0;
-}
-
 static void rspi_dma_complete(void *arg)
 {
 	struct rspi_data *rspi = arg;
···
 
 static int qspi_transfer_out(struct rspi_data *rspi, struct spi_transfer *xfer)
 {
+	const u8 *tx = xfer->tx_buf;
+	unsigned int n = xfer->len;
+	unsigned int i, len;
 	int ret;
 
 	if (rspi->master->can_dma && __rspi_can_dma(rspi, xfer)) {
···
 			return ret;
 	}
 
-	ret = rspi_pio_transfer_in_or_our(rspi, xfer->tx_buf, NULL, xfer->len);
-	if (ret < 0)
-		return ret;
+	while (n > 0) {
+		len = qspi_set_send_trigger(rspi, n);
+		if (len == QSPI_BUFFER_SIZE) {
+			ret = rspi_wait_for_tx_empty(rspi);
+			if (ret < 0) {
+				dev_err(&rspi->master->dev, "transmit timeout\n");
+				return ret;
+			}
+			for (i = 0; i < len; i++)
+				rspi_write_data(rspi, *tx++);
+		} else {
+			ret = rspi_pio_transfer(rspi, tx, NULL, n);
+			if (ret < 0)
+				return ret;
+		}
+		n -= len;
+	}
 
 	/* Wait for the last transmission */
 	rspi_wait_for_tx_empty(rspi);
···
 
 static int qspi_transfer_in(struct rspi_data *rspi, struct spi_transfer *xfer)
 {
+	u8 *rx = xfer->rx_buf;
+	unsigned int n = xfer->len;
+	unsigned int i, len;
+	int ret;
+
 	if (rspi->master->can_dma && __rspi_can_dma(rspi, xfer)) {
 		int ret = rspi_dma_transfer(rspi, NULL, &xfer->rx_sg);
 		if (ret != -EAGAIN)
 			return ret;
 	}
 
-	return rspi_pio_transfer_in_or_our(rspi, NULL, xfer->rx_buf, xfer->len);
+	while (n > 0) {
+		len = qspi_set_receive_trigger(rspi, n);
+		if (len == QSPI_BUFFER_SIZE) {
+			ret = rspi_wait_for_rx_full(rspi);
+			if (ret < 0) {
+				dev_err(&rspi->master->dev, "receive timeout\n");
+				return ret;
+			}
+			for (i = 0; i < len; i++)
+				*rx++ = rspi_read_data(rspi);
+		} else {
+			ret = rspi_pio_transfer(rspi, NULL, rx, n);
+			if (ret < 0)
+				return ret;
+			*rx++ = ret;
+		}
+		n -= len;
+	}
+
+	return 0;
 }
 
 static int qspi_transfer_one(struct spi_master *master, struct spi_device *spi,