spi: fsl-espi: eliminate need for linearization when reading from hardware

Eliminate need for linearization when reading from the hardware and
write to the transfer buffers directly.

Signed-off-by: Heiner Kallweit <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-fsl-espi.c

···
 	struct spi_transfer *tx_t;
 	unsigned int tx_pos;
 	bool tx_done;
+	struct spi_transfer *rx_t;
+	unsigned int rx_pos;
+	bool rx_done;
 
 	bool swab;
 	unsigned int rx_len;
···
 static inline u32 fsl_espi_read_reg(struct fsl_espi *espi, int offset)
 {
 	return ioread32be(espi->reg_base + offset);
+}
+
+static inline u16 fsl_espi_read_reg16(struct fsl_espi *espi, int offset)
+{
+	return ioread16(espi->reg_base + offset);
 }
 
 static inline u8 fsl_espi_read_reg8(struct fsl_espi *espi, int offset)
···
 static void fsl_espi_read_rx_fifo(struct fsl_espi *espi, u32 events)
 {
 	u32 rx_fifo_avail = SPIE_RXCNT(events);
+	unsigned int rx_left;
+	void *rx_buf;
 
-	while (rx_fifo_avail >= min(4U, espi->rx_len) && espi->rx_len)
-		if (espi->rx_len >= 4) {
-			*(u32 *)espi->rx = fsl_espi_read_reg(espi, ESPI_SPIRF);
-			espi->rx += 4;
-			espi->rx_len -= 4;
+start:
+	rx_left = espi->rx_t->len - espi->rx_pos;
+	rx_buf = espi->rx_t->rx_buf;
+	while (rx_fifo_avail >= min(4U, rx_left) && rx_left) {
+		if (rx_left >= 4) {
+			u32 val = fsl_espi_read_reg(espi, ESPI_SPIRF);
+
+			if (rx_buf && espi->swab)
+				*(u32 *)(rx_buf + espi->rx_pos) = swahb32(val);
+			else if (rx_buf)
+				*(u32 *)(rx_buf + espi->rx_pos) = val;
+			espi->rx_pos += 4;
+			rx_left -= 4;
 			rx_fifo_avail -= 4;
+		} else if (rx_left >= 2 && rx_buf && espi->swab) {
+			u16 val = fsl_espi_read_reg16(espi, ESPI_SPIRF);
+
+			*(u16 *)(rx_buf + espi->rx_pos) = swab16(val);
+			espi->rx_pos += 2;
+			rx_left -= 2;
+			rx_fifo_avail -= 2;
 		} else {
-			*(u8 *)espi->rx = fsl_espi_read_reg8(espi, ESPI_SPIRF);
-			espi->rx += 1;
-			espi->rx_len -= 1;
+			u8 val = fsl_espi_read_reg8(espi, ESPI_SPIRF);
+
+			if (rx_buf)
+				*(u8 *)(rx_buf + espi->rx_pos) = val;
+			espi->rx_pos += 1;
+			rx_left -= 1;
 			rx_fifo_avail -= 1;
 		}
+	}
+
+	if (!rx_left) {
+		if (list_is_last(&espi->rx_t->transfer_list,
+		    espi->m_transfers)) {
+			espi->rx_done = true;
+			return;
+		}
+		espi->rx_t = list_next_entry(espi->rx_t, transfer_list);
+		espi->rx_pos = 0;
+		/* continue with next transfer if rx fifo is not empty */
+		if (rx_fifo_avail)
+			goto start;
+	}
 }
 
 static void fsl_espi_setup_transfer(struct spi_device *spi,
···
 static int fsl_espi_bufs(struct spi_device *spi, struct spi_transfer *t)
 {
 	struct fsl_espi *espi = spi_master_get_devdata(spi->master);
+	unsigned int rx_len = t->len;
 	u32 mask, spcom;
 	int ret;
 
···
 		spcom |= SPCOM_RXSKIP(espi->rxskip);
 		espi->tx_len = espi->rxskip;
 		espi->rx_len = t->len - espi->rxskip;
+		rx_len = t->len - espi->rxskip;
 		espi->rx = t->rx_buf + espi->rxskip;
 		if (t->rx_nbits == SPI_NBITS_DUAL)
 			spcom |= SPCOM_DO;
···
 
 	/* enable interrupts */
 	mask = SPIM_DON;
-	if (espi->rx_len > FSL_ESPI_FIFO_SIZE)
+	if (rx_len > FSL_ESPI_FIFO_SIZE)
 		mask |= SPIM_RXT;
 	fsl_espi_write_reg(espi, ESPI_SPIM, mask);
 
···
 				      transfer_list);
 	espi->tx_pos = 0;
 	espi->tx_done = false;
+	espi->rx_t = list_first_entry(&m->transfers, struct spi_transfer,
+				      transfer_list);
+	espi->rx_pos = 0;
+	espi->rx_done = false;
 
 	espi->rxskip = fsl_espi_check_rxskip_mode(m);
 	if (trans->rx_nbits == SPI_NBITS_DUAL && !espi->rxskip) {
 		dev_err(espi->dev, "Dual output mode requires RXSKIP mode!\n");
 		return -EINVAL;
 	}
+
+	/* In RXSKIP mode skip first transfer for reads */
+	if (espi->rxskip)
+		espi->rx_t = list_next_entry(espi->rx_t, transfer_list);
 
 	fsl_espi_copy_to_buf(m, espi);
 	fsl_espi_setup_transfer(spi, trans);
···
 
 	if (trans->delay_usecs)
 		udelay(trans->delay_usecs);
-
-	if (!ret)
-		fsl_espi_copy_from_buf(m, espi);
 
 	return ret;
 }
···
 
 static void fsl_espi_cpu_irq(struct fsl_espi *espi, u32 events)
 {
-	if (espi->rx_len)
+	if (!espi->rx_done)
 		fsl_espi_read_rx_fifo(espi, events);
 
 	if (!espi->tx_done)
 		fsl_espi_fill_tx_fifo(espi, events);
 
-	if (!espi->tx_done || espi->rx_len)
+	if (!espi->tx_done || !espi->rx_done)
 		return;
 
 	/* we're done, but check for errors before returning */