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  * ToDo: Maybe the bitrev macros can be used to improve the code?
  46  */
  47
  48 static inline u32
  49 bitbang_txrx_be_cpha0(struct spi_device *spi,
  50                 unsigned nsecs, unsigned cpol, unsigned flags,
  51                 u32 word, u8 bits)
  52 {
  53         /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
  54
  55         u32 oldbit = (!(word & (1<<(bits-1)))) << 31;
  56         /* clock starts at inactive polarity */
  57         for (word <<= (32 - bits); likely(bits); bits--) {
  58
  59                 /* setup MSB (to slave) on trailing edge */
  60                 if ((flags & SPI_MASTER_NO_TX) == 0) {
  61                         if ((word & (1 << 31)) != oldbit) {
  62                                 setmosi(spi, word & (1 << 31));
  63                                 oldbit = word & (1 << 31);
  64                         }
  65                 }
  66                 spidelay(nsecs);        /* T(setup) */
  67
  68                 setsck(spi, !cpol);
  69                 spidelay(nsecs);
  70
  71                 /* sample MSB (from slave) on leading edge */
  72                 word <<= 1;
  73                 if ((flags & SPI_MASTER_NO_RX) == 0)
  74                         word |= getmiso(spi);
  75                 setsck(spi, cpol);
  76         }
  77         return word;
  78 }
  79
  80 static inline u32
  81 bitbang_txrx_be_cpha1(struct spi_device *spi,
  82                 unsigned nsecs, unsigned cpol, unsigned flags,
  83                 u32 word, u8 bits)
  84 {
  85         /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
  86
  87         u32 oldbit = (!(word & (1<<(bits-1)))) << 31;
  88         /* clock starts at inactive polarity */
  89         for (word <<= (32 - bits); likely(bits); bits--) {
  90
  91                 /* setup MSB (to slave) on leading edge */
  92                 setsck(spi, !cpol);
  93                 if ((flags & SPI_MASTER_NO_TX) == 0) {
  94                         if ((word & (1 << 31)) != oldbit) {
  95                                 setmosi(spi, word & (1 << 31));
  96                                 oldbit = word & (1 << 31);
  97                         }
  98                 }
  99                 spidelay(nsecs); /* T(setup) */
 100
 101                 setsck(spi, cpol);
 102                 spidelay(nsecs);
 103
 104                 /* sample MSB (from slave) on trailing edge */
 105                 word <<= 1;
 106                 if ((flags & SPI_MASTER_NO_RX) == 0)
 107                         word |= getmiso(spi);
 108         }
 109         return word;
 110 }
 111
 112 static inline u32
 113 bitbang_txrx_le_cpha0(struct spi_device *spi,
 114                 unsigned int nsecs, unsigned int cpol, unsigned int flags,
 115                 u32 word, u8 bits)
 116 {
 117         /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
 118
 119         u32 oldbit = !(word & 1);
 120         /* clock starts at inactive polarity */
 121         for (; likely(bits); bits--) {
 122
 123                 /* setup LSB (to slave) on trailing edge */
 124                 if ((flags & SPI_MASTER_NO_TX) == 0) {
 125                         if ((word & 1) != oldbit) {
 126                                 setmosi(spi, word & 1);
 127                                 oldbit = word & 1;
 128                         }
 129                 }
 130                 spidelay(nsecs);        /* T(setup) */
 131
 132                 setsck(spi, !cpol);
 133                 spidelay(nsecs);
 134
 135                 /* sample LSB (from slave) on leading edge */
 136                 word >>= 1;
 137                 if ((flags & SPI_MASTER_NO_RX) == 0)
 138                         word |= getmiso(spi) << (bits - 1);
 139                 setsck(spi, cpol);
 140         }
 141         return word;
 142 }
 143
 144 static inline u32
 145 bitbang_txrx_le_cpha1(struct spi_device *spi,
 146                 unsigned int nsecs, unsigned int cpol, unsigned int flags,
 147                 u32 word, u8 bits)
 148 {
 149         /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
 150
 151         u32 oldbit = !(word & 1);
 152         /* clock starts at inactive polarity */
 153         for (; likely(bits); bits--) {
 154
 155                 /* setup LSB (to slave) on leading edge */
 156                 setsck(spi, !cpol);
 157                 if ((flags & SPI_MASTER_NO_TX) == 0) {
 158                         if ((word & 1) != oldbit) {
 159                                 setmosi(spi, word & 1);
 160                                 oldbit = word & 1;
 161                         }
 162                 }
 163                 spidelay(nsecs); /* T(setup) */
 164
 165                 setsck(spi, cpol);
 166                 spidelay(nsecs);
 167
 168                 /* sample LSB (from slave) on trailing edge */
 169                 word >>= 1;
 170                 if ((flags & SPI_MASTER_NO_RX) == 0)
 171                         word |= getmiso(spi) << (bits - 1);
 172         }
 173         return word;
 174 }