drivers/spi/spi-bitbang-txrx.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * Mix this utility code with some glue code to get one of several types of
   4  * simple SPI master driver.  Two do polled word-at-a-time I/O:
   5  *
   6  *   -  GPIO/parport bitbangers.  Provide chipselect() and txrx_word[](),
   7  *      expanding the per-word routines from the inline templates below.
   8  *
   9  *   -  Drivers for controllers resembling bare shift registers.  Provide
  10  *      chipselect() and txrx_word[](), with custom setup()/cleanup() methods
  11  *      that use your controller's clock and chipselect registers.
  12  *
  13  * Some hardware works well with requests at spi_transfer scope:
  14  *
  15  *   -  Drivers leveraging smarter hardware, with fifos or DMA; or for half
  16  *      duplex (MicroWire) controllers.  Provide chipselect() and txrx_bufs(),
  17  *      and custom setup()/cleanup() methods.
  18  */
  19
  20 /*
  21  * The code that knows what GPIO pins do what should have declared four
  22  * functions, ideally as inlines, before including this header:
  23  *
  24  *  void setsck(struct spi_device *, int is_on);
  25  *  void setmosi(struct spi_device *, int is_on);
  26  *  int getmiso(struct spi_device *);
  27  *  void spidelay(unsigned);
  28  *
  29  * setsck()'s is_on parameter is a zero/nonzero boolean.
  30  *
  31  * setmosi()'s is_on parameter is a zero/nonzero boolean.
  32  *
  33  * getmiso() is required to return 0 or 1 only. Any other value is invalid
  34  * and will result in improper operation.
  35  *
  36  * A non-inlined routine would call bitbang_txrx_*() routines.  The
  37  * main loop could easily compile down to a handful of instructions,
  38  * especially if the delay is a NOP (to run at peak speed).
  39  *
  40  * Since this is software, the timings may not be exactly what your board's
  41  * chips need ... there may be several reasons you'd need to tweak timings
  42  * in these routines, not just to make it faster or slower to match a
  43  * particular CPU clock rate.
  44  */
  45
  46 static inline u32
  47 bitbang_txrx_be_cpha0(struct spi_device *spi,
  48                 unsigned nsecs, unsigned cpol, unsigned flags,
  49                 u32 word, u8 bits)
  50 {
  51         /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
  52
  53         u32 oldbit = (!(word & (1<<(bits-1)))) << 31;
  54         /* clock starts at inactive polarity */
  55         for (word <<= (32 - bits); likely(bits); bits--) {
  56
  57                 /* setup MSB (to slave) on trailing edge */
  58                 if ((flags & SPI_MASTER_NO_TX) == 0) {
  59                         if ((word & (1 << 31)) != oldbit) {
  60                                 setmosi(spi, word & (1 << 31));
  61                                 oldbit = word & (1 << 31);
  62                         }
  63                 }
  64                 spidelay(nsecs);        /* T(setup) */
  65
  66                 setsck(spi, !cpol);
  67                 spidelay(nsecs);
  68
  69                 /* sample MSB (from slave) on leading edge */
  70                 word <<= 1;
  71                 if ((flags & SPI_MASTER_NO_RX) == 0)
  72                         word |= getmiso(spi);
  73                 setsck(spi, cpol);
  74         }
  75         return word;
  76 }
  77
  78 static inline u32
  79 bitbang_txrx_be_cpha1(struct spi_device *spi,
  80                 unsigned nsecs, unsigned cpol, unsigned flags,
  81                 u32 word, u8 bits)
  82 {
  83         /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
  84
  85         u32 oldbit = (!(word & (1<<(bits-1)))) << 31;
  86         /* clock starts at inactive polarity */
  87         for (word <<= (32 - bits); likely(bits); bits--) {
  88
  89                 /* setup MSB (to slave) on leading edge */
  90                 setsck(spi, !cpol);
  91                 if ((flags & SPI_MASTER_NO_TX) == 0) {
  92                         if ((word & (1 << 31)) != oldbit) {
  93                                 setmosi(spi, word & (1 << 31));
  94                                 oldbit = word & (1 << 31);
  95                         }
  96                 }
  97                 spidelay(nsecs); /* T(setup) */
  98
  99                 setsck(spi, cpol);
 100                 spidelay(nsecs);
 101
 102                 /* sample MSB (from slave) on trailing edge */
 103                 word <<= 1;
 104                 if ((flags & SPI_MASTER_NO_RX) == 0)
 105                         word |= getmiso(spi);
 106         }
 107         return word;
 108 }