spi/bcm63xx: reject transfers unable to transfer

The hardware does not support keeping CS asserted after sending one
FIFO buffer worth of data, so reject transfers requiring CS being kept
asserted, either between transers or for a certain time after it,
or exceeding the FIFO size.
Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Acked-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/spi/spi-bcm63xx.c

@@ -49,16 +49,10 @@ struct bcm63xx_spi {
 	unsigned int		msg_type_shift;
 	unsigned int		msg_ctl_width;
 
-	/* Data buffers */
-	const unsigned char	*tx_ptr;
-	unsigned char		*rx_ptr;
-
 	/* data iomem */
 	u8 __iomem		*tx_io;
 	const u8 __iomem	*rx_io;
 
-	int			remaining_bytes;
-
 	struct clk		*clk;
 	struct platform_device	*pdev;
 };
@@ -175,24 +169,13 @@ static int bcm63xx_spi_setup(struct spi_device *spi)
 	return 0;
 }
 
-/* Fill the TX FIFO with as many bytes as possible */
-static void bcm63xx_spi_fill_tx_fifo(struct bcm63xx_spi *bs)
-{
-	u8 size;
-
-	/* Fill the Tx FIFO with as many bytes as possible */
-	size = bs->remaining_bytes < bs->fifo_size ? bs->remaining_bytes :
-		bs->fifo_size;
-	memcpy_toio(bs->tx_io, bs->tx_ptr, size);
-	bs->remaining_bytes -= size;
-}
-
-static unsigned int bcm63xx_txrx_bufs(struct spi_device *spi,
-					struct spi_transfer *t)
+static int bcm63xx_txrx_bufs(struct spi_device *spi, struct spi_transfer *t)
 {
 	struct bcm63xx_spi *bs = spi_master_get_devdata(spi->master);
 	u16 msg_ctl;
 	u16 cmd;
+	u8 rx_tail;
+	unsigned int timeout = 0;
 
 	/* Disable the CMD_DONE interrupt */
 	bcm_spi_writeb(bs, 0, SPI_INT_MASK);
@@ -200,14 +183,8 @@ static unsigned int bcm63xx_txrx_bufs(struct spi_device *spi,
 	dev_dbg(&spi->dev, "txrx: tx %p, rx %p, len %d\n",
 		t->tx_buf, t->rx_buf, t->len);
 
-	/* Transmitter is inhibited */
-	bs->tx_ptr = t->tx_buf;
-	bs->rx_ptr = t->rx_buf;
-
-	if (t->tx_buf) {
-		bs->remaining_bytes = t->len;
-		bcm63xx_spi_fill_tx_fifo(bs);
-	}
+	if (t->tx_buf)
+		memcpy_toio(bs->tx_io, t->tx_buf, t->len);
 
 	init_completion(&bs->done);
 
@@ -239,7 +216,18 @@ static unsigned int bcm63xx_txrx_bufs(struct spi_device *spi,
 	/* Enable the CMD_DONE interrupt */
 	bcm_spi_writeb(bs, SPI_INTR_CMD_DONE, SPI_INT_MASK);
 
-	return t->len - bs->remaining_bytes;
+	timeout = wait_for_completion_timeout(&bs->done, HZ);
+	if (!timeout)
+		return -ETIMEDOUT;
+
+	/* read out all data */
+	rx_tail = bcm_spi_readb(bs, SPI_RX_TAIL);
+
+	/* Read out all the data */
+	if (rx_tail)
+		memcpy_fromio(t->rx_ptr, bs->rx_io, rx_tail);
+
+	return 0;
 }
 
 static int bcm63xx_spi_prepare_transfer(struct spi_master *master)
@@ -267,36 +255,41 @@ static int bcm63xx_spi_transfer_one(struct spi_master *master,
 	struct spi_transfer *t;
 	struct spi_device *spi = m->spi;
 	int status = 0;
-	unsigned int timeout = 0;
 
 	list_for_each_entry(t, &m->transfers, transfer_list) {
-		unsigned int len = t->len;
-		u8 rx_tail;
-
 		status = bcm63xx_spi_check_transfer(spi, t);
 		if (status < 0)
 			goto exit;
 
-		/* configure adapter for a new transfer */
-		bcm63xx_spi_setup_transfer(spi, t);
+		/* we can only transfer one fifo worth of data */
+		if (t->len > bs->fifo_size) {
+			dev_err(&spi->dev, "unable to do transfers larger than FIFO size (%i > %i)\n",
+				t->len, bs->fifo_size);
+			status = -EINVAL;
+			goto exit;
+		}
 
-		while (len) {
-			/* send the data */
-			len -= bcm63xx_txrx_bufs(spi, t);
+		/* CS will be deasserted directly after transfer */
+		if (t->delay_usecs) {
+			dev_err(&spi->dev, "unable to keep CS asserted after transfer\n");
+			status = -EINVAL;
+			goto exit;
+		}
 
-			timeout = wait_for_completion_timeout(&bs->done, HZ);
-			if (!timeout) {
-				status = -ETIMEDOUT;
+		if (!t->cs_change &&
+		    !list_is_last(&t->transfer_list, &m->transfers)) {
+			dev_err(&spi->dev, "unable to keep CS asserted between transfers\n");
+			status = -EINVAL;
 			goto exit;
 		}
 
-			/* read out all data */
-			rx_tail = bcm_spi_readb(bs, SPI_RX_TAIL);
+		/* configure adapter for a new transfer */
+		bcm63xx_spi_setup_transfer(spi, t);
 
-			/* Read out all the data */
-			if (rx_tail)
-				memcpy_fromio(bs->rx_ptr, bs->rx_io, rx_tail);
-		}
+		/* send the data */
+		status = bcm63xx_txrx_bufs(spi, t);
+		if (status)
+			goto exit;
 
 		m->actual_length += t->len;
 	}