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spi: Use bitfields for multiple data lines

Message ID 1389374343-393-1-git-send-email-broonie@kernel.org (mailing list archive)
State Accepted
Commit d3fbd457013c0f6d96de461ce0a9cb1f8b73cd0b
Headers show

Commit Message

Mark Brown Jan. 10, 2014, 5:19 p.m. UTC 
From: Mark Brown <broonie@linaro.org>

Trent Piepho observed that since the current realistic maximum number of
data lines is four we can pack the spi_transfer struct more efficiently
if we use a bitfield for the number of bits, allowing the fields to fit
in a single byte along with cs_change.

If space becomes an issue further optimiation is possible by only using
the constants and packing the values chosen for them.

Reported-by: Trent Piepho <tpiepho@gmail.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
---
 include/linux/spi/spi.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
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Patch

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 27a882978c15..77b529e418d5 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -576,8 +576,8 @@  struct spi_transfer {
 	dma_addr_t	rx_dma;
 
 	unsigned	cs_change:1;
-	u8		tx_nbits;
-	u8		rx_nbits;
+	unsigned	tx_nbits:3;
+	unsigned	rx_nbits:3;
 #define	SPI_NBITS_SINGLE	0x01 /* 1bit transfer */
 #define	SPI_NBITS_DUAL		0x02 /* 2bits transfer */
 #define	SPI_NBITS_QUAD		0x04 /* 4bits transfer */