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
bitbang_txrx_be_cpha0(struct spi_device * spi,unsigned nsecs,unsigned cpol,unsigned flags,u32 word,u8 bits)46 bitbang_txrx_be_cpha0(struct spi_device *spi,
47 unsigned nsecs, unsigned cpol, unsigned flags,
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 if ((flags & SPI_MASTER_NO_TX) == 0)
57 setmosi(spi, word & (1 << 31));
58 spidelay(nsecs); /* T(setup) */
59
60 setsck(spi, !cpol);
61 spidelay(nsecs);
62
63 /* sample MSB (from slave) on leading edge */
64 word <<= 1;
65 if ((flags & SPI_MASTER_NO_RX) == 0)
66 word |= getmiso(spi);
67 setsck(spi, cpol);
68 }
69 return word;
70 }
71
72 static inline u32
bitbang_txrx_be_cpha1(struct spi_device * spi,unsigned nsecs,unsigned cpol,unsigned flags,u32 word,u8 bits)73 bitbang_txrx_be_cpha1(struct spi_device *spi,
74 unsigned nsecs, unsigned cpol, unsigned flags,
75 u32 word, u8 bits)
76 {
77 /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
78
79 /* clock starts at inactive polarity */
80 for (word <<= (32 - bits); likely(bits); bits--) {
81
82 /* setup MSB (to slave) on leading edge */
83 setsck(spi, !cpol);
84 if ((flags & SPI_MASTER_NO_TX) == 0)
85 setmosi(spi, word & (1 << 31));
86 spidelay(nsecs); /* T(setup) */
87
88 setsck(spi, cpol);
89 spidelay(nsecs);
90
91 /* sample MSB (from slave) on trailing edge */
92 word <<= 1;
93 if ((flags & SPI_MASTER_NO_RX) == 0)
94 word |= getmiso(spi);
95 }
96 return word;
97 }
98