root/include/linux/spi/spi_bitbang.h

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#ifndef __SPI_BITBANG_H
#define __SPI_BITBANG_H

#include <linux/workqueue.h>

struct spi_bitbang {
        spinlock_t              lock;
        u8                      busy;
        u8                      use_dma;
        u8                      flags;          /* extra spi->mode support */

        struct spi_master       *master;

        /* setup_transfer() changes clock and/or wordsize to match settings
         * for this transfer; zeroes restore defaults from spi_device.
         */
        int     (*setup_transfer)(struct spi_device *spi,
                        struct spi_transfer *t);

        void    (*chipselect)(struct spi_device *spi, int is_on);
#define BITBANG_CS_ACTIVE       1       /* normally nCS, active low */
#define BITBANG_CS_INACTIVE     0

        /* txrx_bufs() may handle dma mapping for transfers that don't
         * already have one (transfer.{tx,rx}_dma is zero), or use PIO
         */
        int     (*txrx_bufs)(struct spi_device *spi, struct spi_transfer *t);

        /* txrx_word[SPI_MODE_*]() just looks like a shift register */
        u32     (*txrx_word[4])(struct spi_device *spi,
                        unsigned nsecs,
                        u32 word, u8 bits);
};

/* you can call these default bitbang->master methods from your custom
 * methods, if you like.
 */
extern int spi_bitbang_setup(struct spi_device *spi);
extern void spi_bitbang_cleanup(struct spi_device *spi);
extern int spi_bitbang_setup_transfer(struct spi_device *spi,
                                      struct spi_transfer *t);

/* start or stop queue processing */
extern int spi_bitbang_start(struct spi_bitbang *spi);
extern void spi_bitbang_stop(struct spi_bitbang *spi);

#endif  /* __SPI_BITBANG_H */
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