[PATCH 4/4] spi: spi-mem.c : Allow address 0 for SPI mem operations

[Xavier Drudis Ferran]

Trying to boot my Rock Pi 4B from its XTX SPI NOR Flash failed when my
custom compiled TF-A had a load address of 0.

The same TF-A booted correctly from MMC.

Add a local variable to spi_mem_exec_op() to determine operation
direction, instead of testing rx_buf or tx_buf for null value, so that
a buffer at RAM address 0 is accepted.

This commit also cuts short a debug dump of the image loaded to show
only the first 0x1000 and the last 0x100 bytes, and not swamping the
serial log. When adding the #define DEBUG to the .c file one can
change these limits at the same time if they don't fit.

Cc: 	Jagan Teki <jagan at amarulasolutions.com>

Signed-off-by: Xavier Drudis Ferran <xdrudis at tinet.cat>
---
 drivers/spi/spi-mem.c | 34 ++++++++++++++++++++++++++--------
 1 file changed, 26 insertions(+), 8 deletions(-)

diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c
index 9c1ede1b61..4dc90addb3 100644
--- a/drivers/spi/spi-mem.c
+++ b/drivers/spi/spi-mem.c
@@ -21,6 +21,8 @@
 #include <spi.h>
 #include <spi-mem.h>
 #include <dm/device_compat.h>
+#define DEBUG_DUMP_START_LENGTH	0x1000
+#define DEBUG_DUMP_END_LENGTH	0x100
 #endif
 
 #ifndef __UBOOT__
@@ -373,12 +375,21 @@ int spi_mem_exec_op(struct spi_slave *slave, const struct spi_mem_op *op)
 	if (msg.actual_length != totalxferlen)
 		return -EIO;
 #else
+	enum spi_mem_data_dir dir = SPI_MEM_NO_DATA;
 
 	if (op->data.nbytes) {
-		if (op->data.dir == SPI_MEM_DATA_IN)
+		dir = op->data.dir;
+		if (dir == SPI_MEM_DATA_IN) {
 			rx_buf = op->data.buf.in;
-		else
+		} else {
 			tx_buf = op->data.buf.out;
+			/**
+			 * keep old behaviour, to assume SPI_MEM_DATA_OUT
+			 * if ever data.nbytes!=0 but data.dir==SPI_MEM_NO_DATA
+			 * (hopefully never)
+			 */
+			dir = SPI_MEM_DATA_OUT;
+		}
 	}
 
 	op_len = op->cmd.nbytes + op->addr.nbytes + op->dummy.nbytes;
@@ -410,7 +421,7 @@ int spi_mem_exec_op(struct spi_slave *slave, const struct spi_mem_op *op)
 	/* 1st transfer: opcode + address + dummy cycles */
 	flag = SPI_XFER_BEGIN;
 	/* Make sure to set END bit if no tx or rx data messages follow */
-	if (!tx_buf && !rx_buf)
+	if (dir == SPI_MEM_NO_DATA)
 		flag |= SPI_XFER_END;
 
 	ret = spi_xfer(slave, op_len * 8, op_buf, NULL, flag);
@@ -418,7 +429,7 @@ int spi_mem_exec_op(struct spi_slave *slave, const struct spi_mem_op *op)
 		return ret;
 
 	/* 2nd transfer: rx or tx data path */
-	if (tx_buf || rx_buf) {
+	if (dir != SPI_MEM_NO_DATA) {
 		ret = spi_xfer(slave, op->data.nbytes * 8, tx_buf,
 			       rx_buf, SPI_XFER_END);
 		if (ret)
@@ -430,10 +441,17 @@ int spi_mem_exec_op(struct spi_slave *slave, const struct spi_mem_op *op)
 	for (i = 0; i < pos; i++)
 		debug("%02x ", op_buf[i]);
 	debug("| [%dB %s] ",
-	      tx_buf || rx_buf ? op->data.nbytes : 0,
-	      tx_buf || rx_buf ? (tx_buf ? "out" : "in") : "-");
-	for (i = 0; i < op->data.nbytes; i++)
-		debug("%02x ", tx_buf ? tx_buf[i] : rx_buf[i]);
+	      op->data.nbytes,
+	      dir == SPI_MEM_DATA_IN ? "in" : (dir == SPI_MEM_DATA_OUT ? "out" : "-"));
+	for (i = 0; i < op->data.nbytes && i < DEBUG_DUMP_START_LENGTH ; i++)
+		debug("%02x ", dir == SPI_MEM_DATA_OUT ? tx_buf[i] : rx_buf[i]);
+	if (op->data.nbytes > DEBUG_DUMP_END_LENGTH && op->data.nbytes > DEBUG_DUMP_START_LENGTH &&
+	    i < op->data.nbytes - DEBUG_DUMP_END_LENGTH) {
+		debug(" ... ");
+		i = op->data.nbytes - DEBUG_DUMP_END_LENGTH;
+	}
+	for (; i < op->data.nbytes  ; i++)
+		debug("%02x ", dir == SPI_MEM_DATA_OUT ? tx_buf[i] : rx_buf[i]);
 	debug("[ret %d]\n", ret);
 
 	if (ret < 0)
-- 
2.20.1