From: Mark Brown <broonie@linaro.org>
Date: Fri, 10 Jan 2014 17:09:53 +0000 (+0000)
Subject: spi: Use bitfields for multiple data lines
X-Git-Url: http://pileus.org/git/?a=commitdiff_plain;h=d3fbd457013c0f6d96de461ce0a9cb1f8b73cd0b;p=~andy%2Flinux

spi: Use bitfields for multiple data lines

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>
---

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 27a882978c1..77b529e418d 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 */