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
bitbang_txrx_be_cpha0(struct spi_device * spi,unsigned nsecs,unsigned cpol,unsigned flags,u32 word,u8 bits)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, word & (1 << 31));
63 oldbit = word & (1 << 31);
64 }
65 }
66 spidelay(nsecs); /* T(setup) */
67
68 setsck(spi, !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, cpol);
76 }
77 return word;
78 }
79
80 static inline u32
bitbang_txrx_be_cpha1(struct spi_device * spi,unsigned nsecs,unsigned cpol,unsigned flags,u32 word,u8 bits)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, !cpol);
93 if ((flags & SPI_CONTROLLER_NO_TX) == 0) {
94 if ((word & (1 << 31)) != oldbit) {
95 setmosi(spi, word & (1 << 31));
96 oldbit = word & (1 << 31);
97 }
98 }
99 spidelay(nsecs); /* T(setup) */
100
101 setsck(spi, 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
bitbang_txrx_le_cpha0(struct spi_device * spi,unsigned int nsecs,unsigned int cpol,unsigned int flags,u32 word,u8 bits)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, word & 1);
128 oldbit = word & 1;
129 }
130 }
131 spidelay(nsecs); /* T(setup) */
132
133 setsck(spi, !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, cpol);
141 }
142 return word;
143 }
144
145 static inline u32
bitbang_txrx_le_cpha1(struct spi_device * spi,unsigned int nsecs,unsigned int cpol,unsigned int flags,u32 word,u8 bits)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, !cpol);
159 if ((flags & SPI_CONTROLLER_NO_TX) == 0) {
160 if ((word & 1) != oldbit) {
161 setmosi(spi, word & 1);
162 oldbit = word & 1;
163 }
164 }
165 spidelay(nsecs); /* T(setup) */
166
167 setsck(spi, 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