spi: Reorder fields in 'struct spi_transfer'

Group some variables based on their sizes to reduce hole and avoid padding.
On x86_64, this shrinks the size from 144 to 128 bytes.

Turn 'timestamped' into a bitfield so that it can be easily merged with
some other bifields and move 'error'.

This should have no real impact on memory allocation because 'struct
spi_transfer' is mostly used on stack, but it can save a few cycles
when the structure is initialized or copied.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/93a051da85a895bc6003aedfb00a13e1c2fc6338.1676370870.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -1927,7 +1927,7 @@ void spi_take_timestamp_post(struct spi_controller *ctlr,
 	/* Capture the resolution of the timestamp */
 	xfer->ptp_sts_word_post = progress;
 
-	xfer->timestamped = true;
+	xfer->timestamped = 1;
 }
 EXPORT_SYMBOL_GPL(spi_take_timestamp_post);
 

include/linux/spi/spi.h

@@ -1022,6 +1022,9 @@ struct spi_transfer {
 	void		*rx_buf;
 	unsigned	len;
 
+#define SPI_TRANS_FAIL_NO_START	BIT(0)
+	u16		error;
+
 	dma_addr_t	tx_dma;
 	dma_addr_t	rx_dma;
 	struct sg_table tx_sg;
@@ -1032,6 +1035,7 @@ struct spi_transfer {
 	unsigned	cs_change:1;
 	unsigned	tx_nbits:3;
 	unsigned	rx_nbits:3;
+	unsigned	timestamped:1;
 #define	SPI_NBITS_SINGLE	0x01 /* 1bit transfer */
 #define	SPI_NBITS_DUAL		0x02 /* 2bits transfer */
 #define	SPI_NBITS_QUAD		0x04 /* 4bits transfer */
@@ -1048,12 +1052,7 @@ struct spi_transfer {
 
 	struct ptp_system_timestamp *ptp_sts;
 
-	bool		timestamped;
-
 	struct list_head transfer_list;
-
-#define SPI_TRANS_FAIL_NO_START	BIT(0)
-	u16		error;
 };
 
 /**