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Linux kernel mirror (for testing)
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kernel
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linux
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#define BITBANG_CS_ACTIVE 1 /* normally nCS, active low */
35#define BITBANG_CS_INACTIVE 0
36
37 /* txrx_bufs() may handle dma mapping for transfers that don't
38 * already have one (transfer.{tx,rx}_dma is zero), or use PIO
39 */
40 int (*txrx_bufs)(struct spi_device *spi, struct spi_transfer *t);
41
42 /* txrx_word[SPI_MODE_*]() just looks like a shift register */
43 u32 (*txrx_word[4])(struct spi_device *spi,
44 unsigned nsecs,
45 u32 word, u8 bits);
46};
47
48/* you can call these default bitbang->master methods from your custom
49 * methods, if you like.
50 */
51extern int spi_bitbang_setup(struct spi_device *spi);
52extern void spi_bitbang_cleanup(const struct spi_device *spi);
53extern int spi_bitbang_transfer(struct spi_device *spi, struct spi_message *m);
54
55/* start or stop queue processing */
56extern int spi_bitbang_start(struct spi_bitbang *spi);
57extern int spi_bitbang_stop(struct spi_bitbang *spi);
58
59#endif /* __SPI_BITBANG_H */
60
61/*-------------------------------------------------------------------------*/
62
63#ifdef EXPAND_BITBANG_TXRX
64
65/*
66 * The code that knows what GPIO pins do what should have declared four
67 * functions, ideally as inlines, before #defining EXPAND_BITBANG_TXRX
68 * and including this header:
69 *
70 * void setsck(struct spi_device *, int is_on);
71 * void setmosi(struct spi_device *, int is_on);
72 * int getmiso(struct spi_device *);
73 * void spidelay(unsigned);
74 *
75 * A non-inlined routine would call bitbang_txrx_*() routines. The
76 * main loop could easily compile down to a handful of instructions,
77 * especially if the delay is a NOP (to run at peak speed).
78 *
79 * Since this is software, the timings may not be exactly what your board's
80 * chips need ... there may be several reasons you'd need to tweak timings
81 * in these routines, not just make to make it faster or slower to match a
82 * particular CPU clock rate.
83 */
84
85static inline u32
86bitbang_txrx_be_cpha0(struct spi_device *spi,
87 unsigned nsecs, unsigned cpol,
88 u32 word, u8 bits)
89{
90 /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
91
92 /* clock starts at inactive polarity */
93 for (word <<= (32 - bits); likely(bits); bits--) {
94
95 /* setup MSB (to slave) on trailing edge */
96 setmosi(spi, word & (1 << 31));
97 spidelay(nsecs); /* T(setup) */
98
99 setsck(spi, !cpol);
100 spidelay(nsecs);
101
102 /* sample MSB (from slave) on leading edge */
103 word <<= 1;
104 word |= getmiso(spi);
105 setsck(spi, cpol);
106 }
107 return word;
108}
109
110static inline u32
111bitbang_txrx_be_cpha1(struct spi_device *spi,
112 unsigned nsecs, unsigned cpol,
113 u32 word, u8 bits)
114{
115 /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
116
117 /* clock starts at inactive polarity */
118 for (word <<= (32 - bits); likely(bits); bits--) {
119
120 /* setup MSB (to slave) on leading edge */
121 setsck(spi, !cpol);
122 setmosi(spi, word & (1 << 31));
123 spidelay(nsecs); /* T(setup) */
124
125 setsck(spi, cpol);
126 spidelay(nsecs);
127
128 /* sample MSB (from slave) on trailing edge */
129 word <<= 1;
130 word |= getmiso(spi);
131 }
132 return word;
133}
134
135#endif /* EXPAND_BITBANG_TXRX */