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gerrit-public.fairphone.software / kernel / msm-5.4 / 9904f22a7202c6b54e96b0cc9870817013c350a1 / . / include / linux / spi / spi_bitbang.h
blob: 8dfe61a445f44e08cc9d56c7007cdc2dbffd6bb3 [file] [log] [blame]
David Brownell9904f222006-01-08 13:34:26 -0800[diff] [blame^]1#ifndef __SPI_BITBANG_H
2#define __SPI_BITBANG_H
3
4/*
5 * Mix this utility code with some glue code to get one of several types of
6 * simple SPI master driver. Two do polled word-at-a-time I/O:
7 *
8 * - GPIO/parport bitbangers. Provide chipselect() and txrx_word[](),
9 * expanding the per-word routines from the inline templates below.
10 *
11 * - Drivers for controllers resembling bare shift registers. Provide
12 * chipselect() and txrx_word[](), with custom setup()/cleanup() methods
13 * that use your controller's clock and chipselect registers.
14 *
15 * Some hardware works well with requests at spi_transfer scope:
16 *
17 * - Drivers leveraging smarter hardware, with fifos or DMA; or for half
18 * duplex (MicroWire) controllers. Provide chipslect() and txrx_bufs(),
19 * and custom setup()/cleanup() methods.
20 */
21struct spi_bitbang {
22 struct workqueue_struct *workqueue;
23 struct work_struct work;
24
25 spinlock_t lock;
26 struct list_head queue;
27 u8 busy;
28 u8 shutdown;
29 u8 use_dma;
30
31 struct spi_master *master;
32
33 void (*chipselect)(struct spi_device *spi, int is_on);
34
35 int (*txrx_bufs)(struct spi_device *spi, struct spi_transfer *t);
36 u32 (*txrx_word[4])(struct spi_device *spi,
37 unsigned nsecs,
38 u32 word, u8 bits);
39};
40
41/* you can call these default bitbang->master methods from your custom
42 * methods, if you like.
43 */
44extern int spi_bitbang_setup(struct spi_device *spi);
45extern void spi_bitbang_cleanup(const struct spi_device *spi);
46extern int spi_bitbang_transfer(struct spi_device *spi, struct spi_message *m);
47
48/* start or stop queue processing */
49extern int spi_bitbang_start(struct spi_bitbang *spi);
50extern int spi_bitbang_stop(struct spi_bitbang *spi);
51
52#endif /* __SPI_BITBANG_H */
53
54/*-------------------------------------------------------------------------*/
55
56#ifdef EXPAND_BITBANG_TXRX
57
58/*
59 * The code that knows what GPIO pins do what should have declared four
60 * functions, ideally as inlines, before #defining EXPAND_BITBANG_TXRX
61 * and including this header:
62 *
63 * void setsck(struct spi_device *, int is_on);
64 * void setmosi(struct spi_device *, int is_on);
65 * int getmiso(struct spi_device *);
66 * void spidelay(unsigned);
67 *
68 * A non-inlined routine would call bitbang_txrx_*() routines. The
69 * main loop could easily compile down to a handful of instructions,
70 * especially if the delay is a NOP (to run at peak speed).
71 *
72 * Since this is software, the timings may not be exactly what your board's
73 * chips need ... there may be several reasons you'd need to tweak timings
74 * in these routines, not just make to make it faster or slower to match a
75 * particular CPU clock rate.
76 */
77
78static inline u32
79bitbang_txrx_be_cpha0(struct spi_device *spi,
80 unsigned nsecs, unsigned cpol,
81 u32 word, u8 bits)
82{
83 /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
84
85 /* clock starts at inactive polarity */
86 for (word <<= (32 - bits); likely(bits); bits--) {
87
88 /* setup MSB (to slave) on trailing edge */
89 setmosi(spi, word & (1 << 31));
90 spidelay(nsecs); /* T(setup) */
91
92 setsck(spi, !cpol);
93 spidelay(nsecs);
94
95 /* sample MSB (from slave) on leading edge */
96 word <<= 1;
97 word |= getmiso(spi);
98 setsck(spi, cpol);
99 }
100 return word;
101}
102
103static inline u32
104bitbang_txrx_be_cpha1(struct spi_device *spi,
105 unsigned nsecs, unsigned cpol,
106 u32 word, u8 bits)
107{
108 /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
109
110 /* clock starts at inactive polarity */
111 for (word <<= (32 - bits); likely(bits); bits--) {
112
113 /* setup MSB (to slave) on leading edge */
114 setsck(spi, !cpol);
115 setmosi(spi, word & (1 << 31));
116 spidelay(nsecs); /* T(setup) */
117
118 setsck(spi, cpol);
119 spidelay(nsecs);
120
121 /* sample MSB (from slave) on trailing edge */
122 word <<= 1;
123 word |= getmiso(spi);
124 }
125 return word;
126}
127
128#endif /* EXPAND_BITBANG_TXRX */