1 | /* SPDX-License-Identifier: GPL-2.0 */ |
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 |
42 | * in these routines, not just to make it faster or slower to match a |
43 | * particular CPU clock rate. |
44 | * |
45 | * ToDo: Maybe the bitrev macros can be used to improve the code? |
46 | */ |
47 | |
48 | static inline u32 |
49 | bitbang_txrx_be_cpha0(struct spi_device *spi, |
50 | unsigned nsecs, unsigned cpol, unsigned flags, |
51 | u32 word, u8 bits) |
52 | { |
53 | /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */ |
54 | |
55 | u32 oldbit = (!(word & (1<<(bits-1)))) << 31; |
56 | /* clock starts at inactive polarity */ |
57 | for (word <<= (32 - bits); likely(bits); bits--) { |
58 | |
59 | /* setup MSB (to slave) on trailing edge */ |
60 | if ((flags & SPI_CONTROLLER_NO_TX) == 0) { |
61 | if ((word & (1 << 31)) != oldbit) { |
62 | setmosi(spi, is_on: word & (1 << 31)); |
63 | oldbit = word & (1 << 31); |
64 | } |
65 | } |
66 | spidelay(nsecs); /* T(setup) */ |
67 | |
68 | setsck(spi, is_on: !cpol); |
69 | spidelay(nsecs); |
70 | |
71 | /* sample MSB (from slave) on leading edge */ |
72 | word <<= 1; |
73 | if ((flags & SPI_CONTROLLER_NO_RX) == 0) |
74 | word |= getmiso(spi); |
75 | setsck(spi, is_on: cpol); |
76 | } |
77 | return word; |
78 | } |
79 | |
80 | static inline u32 |
81 | bitbang_txrx_be_cpha1(struct spi_device *spi, |
82 | unsigned nsecs, unsigned cpol, unsigned flags, |
83 | u32 word, u8 bits) |
84 | { |
85 | /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */ |
86 | |
87 | u32 oldbit = (!(word & (1<<(bits-1)))) << 31; |
88 | /* clock starts at inactive polarity */ |
89 | for (word <<= (32 - bits); likely(bits); bits--) { |
90 | |
91 | /* setup MSB (to slave) on leading edge */ |
92 | setsck(spi, is_on: !cpol); |
93 | if ((flags & SPI_CONTROLLER_NO_TX) == 0) { |
94 | if ((word & (1 << 31)) != oldbit) { |
95 | setmosi(spi, is_on: word & (1 << 31)); |
96 | oldbit = word & (1 << 31); |
97 | } |
98 | } |
99 | spidelay(nsecs); /* T(setup) */ |
100 | |
101 | setsck(spi, is_on: cpol); |
102 | spidelay(nsecs); |
103 | |
104 | /* sample MSB (from slave) on trailing edge */ |
105 | word <<= 1; |
106 | if ((flags & SPI_CONTROLLER_NO_RX) == 0) |
107 | word |= getmiso(spi); |
108 | } |
109 | return word; |
110 | } |
111 | |
112 | static inline u32 |
113 | bitbang_txrx_le_cpha0(struct spi_device *spi, |
114 | unsigned int nsecs, unsigned int cpol, unsigned int flags, |
115 | u32 word, u8 bits) |
116 | { |
117 | /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */ |
118 | |
119 | u8 rxbit = bits - 1; |
120 | u32 oldbit = !(word & 1); |
121 | /* clock starts at inactive polarity */ |
122 | for (; likely(bits); bits--) { |
123 | |
124 | /* setup LSB (to slave) on trailing edge */ |
125 | if ((flags & SPI_CONTROLLER_NO_TX) == 0) { |
126 | if ((word & 1) != oldbit) { |
127 | setmosi(spi, is_on: word & 1); |
128 | oldbit = word & 1; |
129 | } |
130 | } |
131 | spidelay(nsecs); /* T(setup) */ |
132 | |
133 | setsck(spi, is_on: !cpol); |
134 | spidelay(nsecs); |
135 | |
136 | /* sample LSB (from slave) on leading edge */ |
137 | word >>= 1; |
138 | if ((flags & SPI_CONTROLLER_NO_RX) == 0) |
139 | word |= getmiso(spi) << rxbit; |
140 | setsck(spi, is_on: cpol); |
141 | } |
142 | return word; |
143 | } |
144 | |
145 | static inline u32 |
146 | bitbang_txrx_le_cpha1(struct spi_device *spi, |
147 | unsigned int nsecs, unsigned int cpol, unsigned int flags, |
148 | u32 word, u8 bits) |
149 | { |
150 | /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */ |
151 | |
152 | u8 rxbit = bits - 1; |
153 | u32 oldbit = !(word & 1); |
154 | /* clock starts at inactive polarity */ |
155 | for (; likely(bits); bits--) { |
156 | |
157 | /* setup LSB (to slave) on leading edge */ |
158 | setsck(spi, is_on: !cpol); |
159 | if ((flags & SPI_CONTROLLER_NO_TX) == 0) { |
160 | if ((word & 1) != oldbit) { |
161 | setmosi(spi, is_on: word & 1); |
162 | oldbit = word & 1; |
163 | } |
164 | } |
165 | spidelay(nsecs); /* T(setup) */ |
166 | |
167 | setsck(spi, is_on: cpol); |
168 | spidelay(nsecs); |
169 | |
170 | /* sample LSB (from slave) on trailing edge */ |
171 | word >>= 1; |
172 | if ((flags & SPI_CONTROLLER_NO_RX) == 0) |
173 | word |= getmiso(spi) << rxbit; |
174 | } |
175 | return word; |
176 | } |
177 | |