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Commit | Line | Data |
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b2441318 | 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
41c4221c | 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 | |
f21524f5 | 42 | * in these routines, not just to make it faster or slower to match a |
41c4221c | 43 | * particular CPU clock rate. |
44 | */ | |
45 | ||
46 | static inline u32 | |
47 | bitbang_txrx_be_cpha0(struct spi_device *spi, | |
04bb2a03 | 48 | unsigned nsecs, unsigned cpol, unsigned flags, |
41c4221c | 49 | u32 word, u8 bits) |
50 | { | |
51 | /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */ | |
52 | ||
26a67ec4 | 53 | u32 oldbit = (!(word & (1<<(bits-1)))) << 31; |
41c4221c | 54 | /* clock starts at inactive polarity */ |
55 | for (word <<= (32 - bits); likely(bits); bits--) { | |
56 | ||
57 | /* setup MSB (to slave) on trailing edge */ | |
232a5adc MG |
58 | if ((flags & SPI_MASTER_NO_TX) == 0) { |
59 | if ((word & (1 << 31)) != oldbit) { | |
60 | setmosi(spi, word & (1 << 31)); | |
61 | oldbit = word & (1 << 31); | |
62 | } | |
63 | } | |
41c4221c | 64 | spidelay(nsecs); /* T(setup) */ |
65 | ||
66 | setsck(spi, !cpol); | |
67 | spidelay(nsecs); | |
68 | ||
69 | /* sample MSB (from slave) on leading edge */ | |
70 | word <<= 1; | |
04bb2a03 MS |
71 | if ((flags & SPI_MASTER_NO_RX) == 0) |
72 | word |= getmiso(spi); | |
41c4221c | 73 | setsck(spi, cpol); |
74 | } | |
75 | return word; | |
76 | } | |
77 | ||
78 | static inline u32 | |
79 | bitbang_txrx_be_cpha1(struct spi_device *spi, | |
04bb2a03 | 80 | unsigned nsecs, unsigned cpol, unsigned flags, |
41c4221c | 81 | u32 word, u8 bits) |
82 | { | |
83 | /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */ | |
84 | ||
26a67ec4 | 85 | u32 oldbit = (!(word & (1<<(bits-1)))) << 31; |
41c4221c | 86 | /* clock starts at inactive polarity */ |
87 | for (word <<= (32 - bits); likely(bits); bits--) { | |
88 | ||
89 | /* setup MSB (to slave) on leading edge */ | |
90 | setsck(spi, !cpol); | |
232a5adc MG |
91 | if ((flags & SPI_MASTER_NO_TX) == 0) { |
92 | if ((word & (1 << 31)) != oldbit) { | |
93 | setmosi(spi, word & (1 << 31)); | |
94 | oldbit = word & (1 << 31); | |
95 | } | |
96 | } | |
41c4221c | 97 | spidelay(nsecs); /* T(setup) */ |
98 | ||
99 | setsck(spi, cpol); | |
100 | spidelay(nsecs); | |
101 | ||
102 | /* sample MSB (from slave) on trailing edge */ | |
103 | word <<= 1; | |
04bb2a03 MS |
104 | if ((flags & SPI_MASTER_NO_RX) == 0) |
105 | word |= getmiso(spi); | |
41c4221c | 106 | } |
107 | return word; | |
108 | } |