| hartleys | 41c4221 | 2010-05-06 20:51:04 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Mix this utility code with some glue code to get one of several types of |
| 3 | * simple SPI master driver. Two do polled word-at-a-time I/O: |
| 4 | * |
| 5 | * - GPIO/parport bitbangers. Provide chipselect() and txrx_word[](), |
| 6 | * expanding the per-word routines from the inline templates below. |
| 7 | * |
| 8 | * - Drivers for controllers resembling bare shift registers. Provide |
| 9 | * chipselect() and txrx_word[](), with custom setup()/cleanup() methods |
| 10 | * that use your controller's clock and chipselect registers. |
| 11 | * |
| 12 | * Some hardware works well with requests at spi_transfer scope: |
| 13 | * |
| 14 | * - Drivers leveraging smarter hardware, with fifos or DMA; or for half |
| 15 | * duplex (MicroWire) controllers. Provide chipselect() and txrx_bufs(), |
| 16 | * and custom setup()/cleanup() methods. |
| 17 | */ |
| 18 | |
| 19 | /* |
| 20 | * The code that knows what GPIO pins do what should have declared four |
| 21 | * functions, ideally as inlines, before including this header: |
| 22 | * |
| 23 | * void setsck(struct spi_device *, int is_on); |
| 24 | * void setmosi(struct spi_device *, int is_on); |
| 25 | * int getmiso(struct spi_device *); |
| 26 | * void spidelay(unsigned); |
| 27 | * |
| 28 | * setsck()'s is_on parameter is a zero/nonzero boolean. |
| 29 | * |
| 30 | * setmosi()'s is_on parameter is a zero/nonzero boolean. |
| 31 | * |
| 32 | * getmiso() is required to return 0 or 1 only. Any other value is invalid |
| 33 | * and will result in improper operation. |
| 34 | * |
| 35 | * A non-inlined routine would call bitbang_txrx_*() routines. The |
| 36 | * main loop could easily compile down to a handful of instructions, |
| 37 | * especially if the delay is a NOP (to run at peak speed). |
| 38 | * |
| 39 | * Since this is software, the timings may not be exactly what your board's |
| 40 | * chips need ... there may be several reasons you'd need to tweak timings |
| 41 | * in these routines, not just make to make it faster or slower to match a |
| 42 | * particular CPU clock rate. |
| 43 | */ |
| 44 | |
| 45 | static inline u32 |
| 46 | bitbang_txrx_be_cpha0(struct spi_device *spi, |
| 47 | unsigned nsecs, unsigned cpol, |
| 48 | u32 word, u8 bits) |
| 49 | { |
| 50 | /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */ |
| 51 | |
| 52 | /* clock starts at inactive polarity */ |
| 53 | for (word <<= (32 - bits); likely(bits); bits--) { |
| 54 | |
| 55 | /* setup MSB (to slave) on trailing edge */ |
| 56 | setmosi(spi, word & (1 << 31)); |
| 57 | spidelay(nsecs); /* T(setup) */ |
| 58 | |
| 59 | setsck(spi, !cpol); |
| 60 | spidelay(nsecs); |
| 61 | |
| 62 | /* sample MSB (from slave) on leading edge */ |
| 63 | word <<= 1; |
| 64 | word |= getmiso(spi); |
| 65 | setsck(spi, cpol); |
| 66 | } |
| 67 | return word; |
| 68 | } |
| 69 | |
| 70 | static inline u32 |
| 71 | bitbang_txrx_be_cpha1(struct spi_device *spi, |
| 72 | unsigned nsecs, unsigned cpol, |
| 73 | u32 word, u8 bits) |
| 74 | { |
| 75 | /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */ |
| 76 | |
| 77 | /* clock starts at inactive polarity */ |
| 78 | for (word <<= (32 - bits); likely(bits); bits--) { |
| 79 | |
| 80 | /* setup MSB (to slave) on leading edge */ |
| 81 | setsck(spi, !cpol); |
| 82 | setmosi(spi, word & (1 << 31)); |
| 83 | spidelay(nsecs); /* T(setup) */ |
| 84 | |
| 85 | setsck(spi, cpol); |
| 86 | spidelay(nsecs); |
| 87 | |
| 88 | /* sample MSB (from slave) on trailing edge */ |
| 89 | word <<= 1; |
| 90 | word |= getmiso(spi); |
| 91 | } |
| 92 | return word; |
| 93 | } |