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spi: Use bitfields for multiple data lines

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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>
This commit is contained in:
Mark Brown 2014-01-10 17:09:53 +00:00
commit d3fbd45701
1 changed files with 2 additions and 2 deletions
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4
include/linux/spi/spi.h
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@ -576,8 +576,8 @@ struct spi_transfer {
dma_addr_t rx_dma; dma_addr_t rx_dma;
unsigned cs_change:1; unsigned cs_change:1;
u8 tx_nbits; unsigned tx_nbits:3;
u8 rx_nbits; unsigned rx_nbits:3;
#define SPI_NBITS_SINGLE 0x01 /* 1bit transfer */ #define SPI_NBITS_SINGLE 0x01 /* 1bit transfer */
#define SPI_NBITS_DUAL 0x02 /* 2bits transfer */ #define SPI_NBITS_DUAL 0x02 /* 2bits transfer */
#define SPI_NBITS_QUAD 0x04 /* 4bits transfer */ #define SPI_NBITS_QUAD 0x04 /* 4bits transfer */