spi: spi-s3c64xx: Allow higher transfer lengths in polling IO mode

Some variants of the SPI controller have no DMA support, in such case
SPI transfers longer than the FIFO length are not currently properly
handled by the driver. Fix it by doing multiple transfers in the
s3c64xx_spi_transfer_one() function if the SPI transfer length exceeds
the FIFO size.
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Reviewed-by: Andi Shyti <andi@etezian.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-s3c64xx.c

@@ -635,11 +635,14 @@ static int s3c64xx_spi_transfer_one(struct spi_master *master,
 {
 	struct s3c64xx_spi_driver_data *sdd = spi_master_get_devdata(master);
 	const unsigned int fifo_len = (FIFO_LVL_MASK(sdd) >> 1) + 1;
+	const void *tx_buf = NULL;
+	void *rx_buf = NULL;
+	int target_len = 0, origin_len = 0;
+	int use_dma = 0;
 	int status;
 	u32 speed;
 	u8 bpw;
 	unsigned long flags;
-	int use_dma;
 
 	reinit_completion(&sdd->xfer_completion);
 
@@ -654,12 +657,21 @@ static int s3c64xx_spi_transfer_one(struct spi_master *master,
 		s3c64xx_spi_config(sdd);
 	}
 
-	/* Polling method for xfers not bigger than FIFO capacity */
-	use_dma = 0;
 	if (!is_polling(sdd) && (xfer->len > fifo_len) &&
-	    sdd->rx_dma.ch && sdd->tx_dma.ch)
+	    sdd->rx_dma.ch && sdd->tx_dma.ch) {
 		use_dma = 1;
 
+	} else if (is_polling(sdd) && xfer->len > fifo_len) {
+		tx_buf = xfer->tx_buf;
+		rx_buf = xfer->rx_buf;
+		origin_len = xfer->len;
+
+		target_len = xfer->len;
+		if (xfer->len > fifo_len)
+			xfer->len = fifo_len;
+	}
+
+	do {
 		spin_lock_irqsave(&sdd->lock, flags);
 
 		/* Pending only which is to be done */
@@ -679,23 +691,44 @@ static int s3c64xx_spi_transfer_one(struct spi_master *master,
 			status = s3c64xx_wait_for_pio(sdd, xfer);
 
 		if (status) {
-		dev_err(&spi->dev, "I/O Error: rx-%d tx-%d res:rx-%c tx-%c len-%d\n",
+			dev_err(&spi->dev,
+				"I/O Error: rx-%d tx-%d res:rx-%c tx-%c len-%d\n",
 				xfer->rx_buf ? 1 : 0, xfer->tx_buf ? 1 : 0,
 				(sdd->state & RXBUSY) ? 'f' : 'p',
 				(sdd->state & TXBUSY) ? 'f' : 'p',
 				xfer->len);
 
 			if (use_dma) {
-			if (xfer->tx_buf != NULL
-			    && (sdd->state & TXBUSY))
+				if (xfer->tx_buf && (sdd->state & TXBUSY))
 					dmaengine_terminate_all(sdd->tx_dma.ch);
-			if (xfer->rx_buf != NULL
-			    && (sdd->state & RXBUSY))
+				if (xfer->rx_buf && (sdd->state & RXBUSY))
 					dmaengine_terminate_all(sdd->rx_dma.ch);
 			}
 		} else {
 			s3c64xx_flush_fifo(sdd);
 		}
+		if (target_len > 0) {
+			target_len -= xfer->len;
+
+			if (xfer->tx_buf)
+				xfer->tx_buf += xfer->len;
+
+			if (xfer->rx_buf)
+				xfer->rx_buf += xfer->len;
+
+			if (target_len > fifo_len)
+				xfer->len = fifo_len;
+			else
+				xfer->len = target_len;
+		}
+	} while (target_len > 0);
+
+	if (origin_len) {
+		/* Restore original xfer buffers and length */
+		xfer->tx_buf = tx_buf;
+		xfer->rx_buf = rx_buf;
+		xfer->len = origin_len;
+	}
 
 	return status;
 }