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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 | */ | |
21 | struct 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 | */ | |
44 | extern int spi_bitbang_setup(struct spi_device *spi); | |
45 | extern void spi_bitbang_cleanup(const struct spi_device *spi); | |
46 | extern int spi_bitbang_transfer(struct spi_device *spi, struct spi_message *m); | |
47 | ||
48 | /* start or stop queue processing */ | |
49 | extern int spi_bitbang_start(struct spi_bitbang *spi); | |
50 | extern 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 | ||
78 | static inline u32 | |
79 | bitbang_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 | ||
103 | static inline u32 | |
104 | bitbang_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 */ |