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spi: Add Flag to Enable Slave Select with GPIO Chip Select.

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Some SPI masters require slave selection before the transfer
can begin [1]. The SPI framework currently selects the chip using
either 1) the internal CS mechanism or 2) the GPIO CS, but not both.

This patch adds a new master->flags define to indicate both the GPIO
CS and the internal chip select mechanism should be used.

Tested On:
    Altera CycloneV development kit
    Compile tested for build errors on x86_64 (allyesconfigs)

[1] DesignWare dw_apb_ssi Databook, Version 3.20a (page 39)

Signed-off-by: Thor Thayer <tthayer@opensource.altera.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Thor Thayer 2016-10-10 09:25:24 -05:00 committed by Mark Brown
parent 1001354ca3
commit 8eee6b9dd3
2 changed files with 8 additions and 2 deletions
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9
drivers/spi/spi.c
View File

@ -697,10 +697,15 @@ static void spi_set_cs(struct spi_device *spi, bool enable)
if (spi->mode & SPI_CS_HIGH)
enable = !enable;
if (gpio_is_valid(spi->cs_gpio))
if (gpio_is_valid(spi->cs_gpio)) {
gpio_set_value(spi->cs_gpio, !enable);
else if (spi->master->set_cs)
/* Some SPI masters need both GPIO CS & slave_select */
if ((spi->master->flags & SPI_MASTER_GPIO_SS) &&
spi->master->set_cs)
spi->master->set_cs(spi, !enable);
} else if (spi->master->set_cs) {
spi->master->set_cs(spi, !enable);
}
}
#ifdef CONFIG_HAS_DMA

1
include/linux/spi/spi.h
View File

@ -442,6 +442,7 @@ struct spi_master {
#define SPI_MASTER_NO_TX BIT(2) /* can't do buffer write */
#define SPI_MASTER_MUST_RX BIT(3) /* requires rx */
#define SPI_MASTER_MUST_TX BIT(4) /* requires tx */
#define SPI_MASTER_GPIO_SS BIT(5) /* GPIO CS must select slave */
/*
* on some hardware transfer / message size may be constrained