include/linux/spi/spi_bitbang.h

   1 #ifndef __SPI_BITBANG_H
   2 #define __SPI_BITBANG_H
   3
   4 /*
   5  * Mix this utility code with some glue code to get one of several types of
   6  * simple SPI master driver.  Two do polled word-at-a-time I/O:
   7  *
   8  *   -  GPIO/parport bitbangers.  Provide chipselect() and txrx_word[](),
   9  *      expanding the per-word routines from the inline templates below.
  10  *
  11  *   -  Drivers for controllers resembling bare shift registers.  Provide
  12  *      chipselect() and txrx_word[](), with custom setup()/cleanup() methods
  13  *      that use your controller's clock and chipselect registers.
  14  *
  15  * Some hardware works well with requests at spi_transfer scope:
  16  *
  17  *   -  Drivers leveraging smarter hardware, with fifos or DMA; or for half
  18  *      duplex (MicroWire) controllers.  Provide chipslect() and txrx_bufs(),
  19  *      and custom setup()/cleanup() methods.
  20  */
  21 struct spi_bitbang {
  22         struct workqueue_struct *workqueue;
  23         struct work_struct      work;
  24
  25         spinlock_t              lock;
  26         struct list_head        queue;
  27         u8                      busy;
  28         u8                      shutdown;
  29         u8                      use_dma;
  30
  31         struct spi_master       *master;
  32
  33         void    (*chipselect)(struct spi_device *spi, int is_on);
  34
  35         int     (*txrx_bufs)(struct spi_device *spi, struct spi_transfer *t);
  36         u32     (*txrx_word[4])(struct spi_device *spi,
  37                         unsigned nsecs,
  38                         u32 word, u8 bits);
  39 };
  40
  41 /* you can call these default bitbang->master methods from your custom
  42  * methods, if you like.
  43  */
  44 extern int spi_bitbang_setup(struct spi_device *spi);
  45 extern void spi_bitbang_cleanup(const struct spi_device *spi);
  46 extern int spi_bitbang_transfer(struct spi_device *spi, struct spi_message *m);
  47
  48 /* start or stop queue processing */
  49 extern int spi_bitbang_start(struct spi_bitbang *spi);
  50 extern int spi_bitbang_stop(struct spi_bitbang *spi);
  51
  52 #endif  /* __SPI_BITBANG_H */
  53
  54 /*-------------------------------------------------------------------------*/
  55
  56 #ifdef  EXPAND_BITBANG_TXRX
  57
  58 /*
  59  * The code that knows what GPIO pins do what should have declared four
  60  * functions, ideally as inlines, before #defining EXPAND_BITBANG_TXRX
  61  * and including this header:
  62  *
  63  *  void setsck(struct spi_device *, int is_on);
  64  *  void setmosi(struct spi_device *, int is_on);
  65  *  int getmiso(struct spi_device *);
  66  *  void spidelay(unsigned);
  67  *
  68  * A non-inlined routine would call bitbang_txrx_*() routines.  The
  69  * main loop could easily compile down to a handful of instructions,
  70  * especially if the delay is a NOP (to run at peak speed).
  71  *
  72  * Since this is software, the timings may not be exactly what your board's
  73  * chips need ... there may be several reasons you'd need to tweak timings
  74  * in these routines, not just make to make it faster or slower to match a
  75  * particular CPU clock rate.
  76  */
  77
  78 static inline u32
  79 bitbang_txrx_be_cpha0(struct spi_device *spi,
  80                 unsigned nsecs, unsigned cpol,
  81                 u32 word, u8 bits)
  82 {
  83         /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
  84
  85         /* clock starts at inactive polarity */
  86         for (word <<= (32 - bits); likely(bits); bits--) {
  87
  88                 /* setup MSB (to slave) on trailing edge */
  89                 setmosi(spi, word & (1 << 31));
  90                 spidelay(nsecs);        /* T(setup) */
  91
  92                 setsck(spi, !cpol);
  93                 spidelay(nsecs);
  94
  95                 /* sample MSB (from slave) on leading edge */
  96                 word <<= 1;
  97                 word |= getmiso(spi);
  98                 setsck(spi, cpol);
  99         }
 100         return word;
 101 }
 102
 103 static inline u32
 104 bitbang_txrx_be_cpha1(struct spi_device *spi,
 105                 unsigned nsecs, unsigned cpol,
 106                 u32 word, u8 bits)
 107 {
 108         /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
 109
 110         /* clock starts at inactive polarity */
 111         for (word <<= (32 - bits); likely(bits); bits--) {
 112
 113                 /* setup MSB (to slave) on leading edge */
 114                 setsck(spi, !cpol);
 115                 setmosi(spi, word & (1 << 31));
 116                 spidelay(nsecs); /* T(setup) */
 117
 118                 setsck(spi, cpol);
 119                 spidelay(nsecs);
 120
 121                 /* sample MSB (from slave) on trailing edge */
 122                 word <<= 1;
 123                 word |= getmiso(spi);
 124         }
 125         return word;
 126 }
 127
 128 #endif  /* EXPAND_BITBANG_TXRX */