spi: amd: Setup all xfers before opcode execution

The AMD SPI controller hardware seems to expect the FIFO buffer to be
fully setup with the details of all transfers in the SPI message before
it is able to start processing the data in a reliable way.

Furthermore, it imposes a strict ordering restriction, in the sense that
all TX transfers must be handled prior any RX transfer.

Hence, let's ensure amd_spi_execute_opcode() is called only once, after
all TX transfers have been setup, and process any remaining RX transfers
afterwards, in a second iteration.

Additionally, get rid of the unnecessary AMD_SPI_XFER_TX/RX defines and
improve error handling.
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Link: https://lore.kernel.org/r/20220818010059.403776-1-cristian.ciocaltea@collabora.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-amd.c

@@ -36,10 +36,6 @@
 #define AMD_SPI_FIFO_SIZE	70
 #define AMD_SPI_MEM_SIZE	200
 
-/* M_CMD OP codes for SPI */
-#define AMD_SPI_XFER_TX		1
-#define AMD_SPI_XFER_RX		2
-
 /**
  * enum amd_spi_versions - SPI controller versions
  * @AMD_SPI_V1:		AMDI0061 hardware version
@@ -194,60 +190,67 @@ static inline int amd_spi_fifo_xfer(struct amd_spi *amd_spi,
 				    struct spi_message *message)
 {
 	struct spi_transfer *xfer = NULL;
-	u8 cmd_opcode;
+	u8 cmd_opcode = 0, fifo_pos = AMD_SPI_FIFO_BASE;
 	u8 *buf = NULL;
-	u32 m_cmd = 0;
 	u32 i = 0;
 	u32 tx_len = 0, rx_len = 0;
 
 	list_for_each_entry(xfer, &message->transfers,
 			    transfer_list) {
-		if (xfer->rx_buf)
-			m_cmd = AMD_SPI_XFER_RX;
-		if (xfer->tx_buf)
-			m_cmd = AMD_SPI_XFER_TX;
-
-		if (m_cmd & AMD_SPI_XFER_TX) {
+		if (xfer->tx_buf) {
 			buf = (u8 *)xfer->tx_buf;
-			tx_len = xfer->len - 1;
+			if (!tx_len) {
 				cmd_opcode = *(u8 *)xfer->tx_buf;
 				buf++;
-			amd_spi_set_opcode(amd_spi, cmd_opcode);
+				xfer->len--;
+			}
+			tx_len += xfer->len;
 
 			/* Write data into the FIFO. */
-			for (i = 0; i < tx_len; i++) {
-				iowrite8(buf[i], ((u8 __iomem *)amd_spi->io_remap_addr +
-					 AMD_SPI_FIFO_BASE + i));
+			for (i = 0; i < xfer->len; i++)
+				amd_spi_writereg8(amd_spi, fifo_pos + i, buf[i]);
+
+			fifo_pos += xfer->len;
 		}
 
-			amd_spi_set_tx_count(amd_spi, tx_len);
-			amd_spi_clear_fifo_ptr(amd_spi);
-			/* Execute command */
-			amd_spi_execute_opcode(amd_spi);
+		/* Store no. of bytes to be received from FIFO */
+		if (xfer->rx_buf)
+			rx_len += xfer->len;
 	}
-		if (m_cmd & AMD_SPI_XFER_RX) {
-			/*
-			 * Store no. of bytes to be received from
-			 * FIFO
-			 */
-			rx_len = xfer->len;
-			buf = (u8 *)xfer->rx_buf;
+
+	if (!buf) {
+		message->status = -EINVAL;
+		goto fin_msg;
+	}
+
+	amd_spi_set_opcode(amd_spi, cmd_opcode);
+	amd_spi_set_tx_count(amd_spi, tx_len);
 	amd_spi_set_rx_count(amd_spi, rx_len);
-			amd_spi_clear_fifo_ptr(amd_spi);
+
 	/* Execute command */
-			amd_spi_execute_opcode(amd_spi);
-			amd_spi_busy_wait(amd_spi);
+	message->status = amd_spi_execute_opcode(amd_spi);
+	if (message->status)
+		goto fin_msg;
+
+	if (rx_len) {
+		message->status = amd_spi_busy_wait(amd_spi);
+		if (message->status)
+			goto fin_msg;
+
+		list_for_each_entry(xfer, &message->transfers, transfer_list)
+			if (xfer->rx_buf) {
+				buf = (u8 *)xfer->rx_buf;
 				/* Read data from FIFO to receive buffer */
-			for (i = 0; i < rx_len; i++)
-				buf[i] = amd_spi_readreg8(amd_spi, AMD_SPI_FIFO_BASE + tx_len + i);
+				for (i = 0; i < xfer->len; i++)
+					buf[i] = amd_spi_readreg8(amd_spi, fifo_pos + i);
+				fifo_pos += xfer->len;
 			}
 	}
 
 	/* Update statistics */
 	message->actual_length = tx_len + rx_len + 1;
-	/* complete the transaction */
-	message->status = 0;
 
+fin_msg:
 	switch (amd_spi->version) {
 	case AMD_SPI_V1:
 		break;
@@ -260,7 +263,7 @@ static inline int amd_spi_fifo_xfer(struct amd_spi *amd_spi,
 
 	spi_finalize_current_message(master);
 
-	return 0;
+	return message->status;
 }
 
 static int amd_spi_master_transfer(struct spi_master *master,
@@ -275,9 +278,7 @@ static int amd_spi_master_transfer(struct spi_master *master,
 	 * Extract spi_transfers from the spi message and
 	 * program the controller.
 	 */
-	amd_spi_fifo_xfer(amd_spi, master, msg);
-
-	return 0;
+	return amd_spi_fifo_xfer(amd_spi, master, msg);
 }
 
 static size_t amd_spi_max_transfer_size(struct spi_device *spi)