spi: axi-spi-engine: small cleanups

Merge series from David Lechner <dlechner@baylibre.com>:

This series contains a few small cleanups to the axi-spi-engine driver,
mostly suggested from previous reviews.

drivers/spi/spi-axi-spi-engine.c

@@ -12,6 +12,7 @@
 #include <linux/io.h>
 #include <linux/of.h>
 #include <linux/module.h>
+#include <linux/overflow.h>
 #include <linux/platform_device.h>
 #include <linux/spi/spi.h>
 
@@ -75,15 +76,13 @@
 
 struct spi_engine_program {
 	unsigned int length;
-	uint16_t instructions[];
+	uint16_t instructions[] __counted_by(length);
 };
 
 /**
  * struct spi_engine_message_state - SPI engine per-message state
  */
 struct spi_engine_message_state {
-	/** @p: Instructions for executing this message. */
-	struct spi_engine_program *p;
 	/** @cmd_length: Number of elements in cmd_buf array. */
 	unsigned cmd_length;
 	/** @cmd_buf: Array of commands not yet written to CMD FIFO. */
@@ -117,9 +116,10 @@ struct spi_engine {
 static void spi_engine_program_add_cmd(struct spi_engine_program *p,
 	bool dry, uint16_t cmd)
 {
-	if (!dry)
-		p->instructions[p->length] = cmd;
 	p->length++;
+
+	if (!dry)
+		p->instructions[p->length - 1] = cmd;
 }
 
 static unsigned int spi_engine_get_config(struct spi_device *spi)
@@ -503,15 +503,13 @@ static irqreturn_t spi_engine_irq(int irq, void *devid)
 static int spi_engine_optimize_message(struct spi_message *msg)
 {
 	struct spi_engine_program p_dry, *p;
-	size_t size;
 
 	spi_engine_precompile_message(msg);
 
 	p_dry.length = 0;
 	spi_engine_compile_message(msg, true, &p_dry);
 
-	size = sizeof(*p->instructions) * (p_dry.length + 1);
-	p = kzalloc(sizeof(*p) + size, GFP_KERNEL);
+	p = kzalloc(struct_size(p, instructions, p_dry.length + 1), GFP_KERNEL);
 	if (!p)
 		return -ENOMEM;
 
@@ -543,7 +541,6 @@ static int spi_engine_transfer_one_message(struct spi_controller *host,
 
 	/* reinitialize message state for this transfer */
 	memset(st, 0, sizeof(*st));
-	st->p = p;
 	st->cmd_buf = p->instructions;
 	st->cmd_length = p->length;
 	msg->state = st;