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_MASTER_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_MASTER_NO_RX) == 0)
74 			word |= getmiso(spi);
75 		setsck(spi, 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, !cpol);
93 		if ((flags & SPI_MASTER_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_MASTER_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_MASTER_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_MASTER_NO_RX) == 0)
139 			word |= getmiso(spi) << rxbit;
140 		setsck(spi, 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, !cpol);
159 		if ((flags & SPI_MASTER_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_MASTER_NO_RX) == 0)
173 			word |= getmiso(spi) << rxbit;
174 	}
175 	return word;
176 }
177