LXR linux/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
  46static inline u32
  47bitbang_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
  78static inline u32
  79bitbang_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}
 109