[U-Boot] [PATCH 17/17] spi: Avoid using malloc() in a critical function

[Simon Glass]

In general we should avoid calling malloc() and free() repeatedly in
U-Boot lest we turn it into tianocore. In SPL this can make SPI flash
unusable since free() is often a nop and allocation space is limited.

In any case, these seems no need for malloc() since the number of bytes
is very small, perhaps less than 8.

Signed-off-by: Simon Glass <sjg at chromium.org>
Fixes: d13f5b254a (spi: Extend the core to ease integration of SPI
	memory controllers)

---

 drivers/spi/spi-mem.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c
index b86eee75bcb..7aabebeff5f 100644
--- a/drivers/spi/spi-mem.c
+++ b/drivers/spi/spi-mem.c
@@ -201,7 +201,6 @@ int spi_mem_exec_op(struct spi_slave *slave, const struct spi_mem_op *op)
 	unsigned int pos = 0;
 	const u8 *tx_buf = NULL;
 	u8 *rx_buf = NULL;
-	u8 *op_buf;
 	int op_len;
 	u32 flag;
 	int ret;
@@ -338,7 +337,17 @@ int spi_mem_exec_op(struct spi_slave *slave, const struct spi_mem_op *op)
 	}
 
 	op_len = sizeof(op->cmd.opcode) + op->addr.nbytes + op->dummy.nbytes;
-	op_buf = calloc(1, op_len);
+
+	/*
+	 * Avoid using malloc() here so that we can use this code in SPL where
+	 * simple malloc may be used. That implementation does not allow free()
+	 * so repeated calls to this code can exhaust the space.
+	 *
+	 * The value of op_len is small, since it does not include the actual
+	 * data being sent, only the op-code and address. In fact, it should be
+	 * possible to just use a small fixed value here instead of op_len.
+	 */
+	u8 op_buf[op_len];
 
 	op_buf[pos++] = op->cmd.opcode;
 
@@ -382,8 +391,6 @@ int spi_mem_exec_op(struct spi_slave *slave, const struct spi_mem_op *op)
 		debug("%02x ", tx_buf ? tx_buf[i] : rx_buf[i]);
 	debug("[ret %d]\n", ret);
 
-	free(op_buf);
-
 	if (ret < 0)
 		return ret;
 #endif /* __UBOOT__ */
-- 
2.21.0.1020.gf2820cf01a-goog