Commit | Line | Data |
---|---|---|
41c4221c | 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 | |
f21524f5 | 41 | * in these routines, not just to make it faster or slower to match a |
41c4221c | 42 | * particular CPU clock rate. |
43 | */ | |
44 | ||
45 | static inline u32 | |
46 | bitbang_txrx_be_cpha0(struct spi_device *spi, | |
04bb2a03 | 47 | unsigned nsecs, unsigned cpol, unsigned flags, |
41c4221c | 48 | u32 word, u8 bits) |
49 | { | |
50 | /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */ | |
51 | ||
232a5adc | 52 | bool oldbit = !(word & 1); |
41c4221c | 53 | /* clock starts at inactive polarity */ |
54 | for (word <<= (32 - bits); likely(bits); bits--) { | |
55 | ||
56 | /* setup MSB (to slave) on trailing edge */ | |
232a5adc MG |
57 | if ((flags & SPI_MASTER_NO_TX) == 0) { |
58 | if ((word & (1 << 31)) != oldbit) { | |
59 | setmosi(spi, word & (1 << 31)); | |
60 | oldbit = word & (1 << 31); | |
61 | } | |
62 | } | |
41c4221c | 63 | spidelay(nsecs); /* T(setup) */ |
64 | ||
65 | setsck(spi, !cpol); | |
66 | spidelay(nsecs); | |
67 | ||
68 | /* sample MSB (from slave) on leading edge */ | |
69 | word <<= 1; | |
04bb2a03 MS |
70 | if ((flags & SPI_MASTER_NO_RX) == 0) |
71 | word |= getmiso(spi); | |
41c4221c | 72 | setsck(spi, cpol); |
73 | } | |
74 | return word; | |
75 | } | |
76 | ||
77 | static inline u32 | |
78 | bitbang_txrx_be_cpha1(struct spi_device *spi, | |
04bb2a03 | 79 | unsigned nsecs, unsigned cpol, unsigned flags, |
41c4221c | 80 | u32 word, u8 bits) |
81 | { | |
82 | /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */ | |
83 | ||
232a5adc | 84 | bool oldbit = !(word & (1 << 31)); |
41c4221c | 85 | /* clock starts at inactive polarity */ |
86 | for (word <<= (32 - bits); likely(bits); bits--) { | |
87 | ||
88 | /* setup MSB (to slave) on leading edge */ | |
89 | setsck(spi, !cpol); | |
232a5adc MG |
90 | if ((flags & SPI_MASTER_NO_TX) == 0) { |
91 | if ((word & (1 << 31)) != oldbit) { | |
92 | setmosi(spi, word & (1 << 31)); | |
93 | oldbit = word & (1 << 31); | |
94 | } | |
95 | } | |
41c4221c | 96 | spidelay(nsecs); /* T(setup) */ |
97 | ||
98 | setsck(spi, cpol); | |
99 | spidelay(nsecs); | |
100 | ||
101 | /* sample MSB (from slave) on trailing edge */ | |
102 | word <<= 1; | |
04bb2a03 MS |
103 | if ((flags & SPI_MASTER_NO_RX) == 0) |
104 | word |= getmiso(spi); | |
41c4221c | 105 | } |
106 | return word; | |
107 | } |