diff options
Diffstat (limited to 'drivers/spi/spi-bitbang-txrx.h')
| -rw-r--r-- | drivers/spi/spi-bitbang-txrx.h | 176 |
1 files changed, 176 insertions, 0 deletions
diff --git a/drivers/spi/spi-bitbang-txrx.h b/drivers/spi/spi-bitbang-txrx.h new file mode 100644 index 000000000..2dcbe166d --- /dev/null +++ b/drivers/spi/spi-bitbang-txrx.h @@ -0,0 +1,176 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Mix this utility code with some glue code to get one of several types of + * simple SPI master driver. Two do polled word-at-a-time I/O: + * + * - GPIO/parport bitbangers. Provide chipselect() and txrx_word[](), + * expanding the per-word routines from the inline templates below. + * + * - Drivers for controllers resembling bare shift registers. Provide + * chipselect() and txrx_word[](), with custom setup()/cleanup() methods + * that use your controller's clock and chipselect registers. + * + * Some hardware works well with requests at spi_transfer scope: + * + * - Drivers leveraging smarter hardware, with fifos or DMA; or for half + * duplex (MicroWire) controllers. Provide chipselect() and txrx_bufs(), + * and custom setup()/cleanup() methods. + */ + +/* + * The code that knows what GPIO pins do what should have declared four + * functions, ideally as inlines, before including this header: + * + * void setsck(struct spi_device *, int is_on); + * void setmosi(struct spi_device *, int is_on); + * int getmiso(struct spi_device *); + * void spidelay(unsigned); + * + * setsck()'s is_on parameter is a zero/nonzero boolean. + * + * setmosi()'s is_on parameter is a zero/nonzero boolean. + * + * getmiso() is required to return 0 or 1 only. Any other value is invalid + * and will result in improper operation. + * + * A non-inlined routine would call bitbang_txrx_*() routines. The + * main loop could easily compile down to a handful of instructions, + * especially if the delay is a NOP (to run at peak speed). + * + * Since this is software, the timings may not be exactly what your board's + * chips need ... there may be several reasons you'd need to tweak timings + * in these routines, not just to make it faster or slower to match a + * particular CPU clock rate. + * + * ToDo: Maybe the bitrev macros can be used to improve the code? + */ + +static inline u32 +bitbang_txrx_be_cpha0(struct spi_device *spi, + unsigned nsecs, unsigned cpol, unsigned flags, + u32 word, u8 bits) +{ + /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */ + + u32 oldbit = (!(word & (1<<(bits-1)))) << 31; + /* clock starts at inactive polarity */ + for (word <<= (32 - bits); likely(bits); bits--) { + + /* setup MSB (to slave) on trailing edge */ + if ((flags & SPI_MASTER_NO_TX) == 0) { + if ((word & (1 << 31)) != oldbit) { + setmosi(spi, word & (1 << 31)); + oldbit = word & (1 << 31); + } + } + spidelay(nsecs); /* T(setup) */ + + setsck(spi, !cpol); + spidelay(nsecs); + + /* sample MSB (from slave) on leading edge */ + word <<= 1; + if ((flags & SPI_MASTER_NO_RX) == 0) + word |= getmiso(spi); + setsck(spi, cpol); + } + return word; +} + +static inline u32 +bitbang_txrx_be_cpha1(struct spi_device *spi, + unsigned nsecs, unsigned cpol, unsigned flags, + u32 word, u8 bits) +{ + /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */ + + u32 oldbit = (!(word & (1<<(bits-1)))) << 31; + /* clock starts at inactive polarity */ + for (word <<= (32 - bits); likely(bits); bits--) { + + /* setup MSB (to slave) on leading edge */ + setsck(spi, !cpol); + if ((flags & SPI_MASTER_NO_TX) == 0) { + if ((word & (1 << 31)) != oldbit) { + setmosi(spi, word & (1 << 31)); + oldbit = word & (1 << 31); + } + } + spidelay(nsecs); /* T(setup) */ + + setsck(spi, cpol); + spidelay(nsecs); + + /* sample MSB (from slave) on trailing edge */ + word <<= 1; + if ((flags & SPI_MASTER_NO_RX) == 0) + word |= getmiso(spi); + } + return word; +} + +static inline u32 +bitbang_txrx_le_cpha0(struct spi_device *spi, + unsigned int nsecs, unsigned int cpol, unsigned int flags, + u32 word, u8 bits) +{ + /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */ + + u8 rxbit = bits - 1; + u32 oldbit = !(word & 1); + /* clock starts at inactive polarity */ + for (; likely(bits); bits--) { + + /* setup LSB (to slave) on trailing edge */ + if ((flags & SPI_MASTER_NO_TX) == 0) { + if ((word & 1) != oldbit) { + setmosi(spi, word & 1); + oldbit = word & 1; + } + } + spidelay(nsecs); /* T(setup) */ + + setsck(spi, !cpol); + spidelay(nsecs); + + /* sample LSB (from slave) on leading edge */ + word >>= 1; + if ((flags & SPI_MASTER_NO_RX) == 0) + word |= getmiso(spi) << rxbit; + setsck(spi, cpol); + } + return word; +} + +static inline u32 +bitbang_txrx_le_cpha1(struct spi_device *spi, + unsigned int nsecs, unsigned int cpol, unsigned int flags, + u32 word, u8 bits) +{ + /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */ + + u8 rxbit = bits - 1; + u32 oldbit = !(word & 1); + /* clock starts at inactive polarity */ + for (; likely(bits); bits--) { + + /* setup LSB (to slave) on leading edge */ + setsck(spi, !cpol); + if ((flags & SPI_MASTER_NO_TX) == 0) { + if ((word & 1) != oldbit) { + setmosi(spi, word & 1); + oldbit = word & 1; + } + } + spidelay(nsecs); /* T(setup) */ + + setsck(spi, cpol); + spidelay(nsecs); + + /* sample LSB (from slave) on trailing edge */ + word >>= 1; + if ((flags & SPI_MASTER_NO_RX) == 0) + word |= getmiso(spi) << rxbit; + } + return word; +} |