1 /*
2  * Mix this utility code with some glue code to get one of several types of
3  * simple SPI master driver.  Two do polled word-at-a-time I/O:
4  *
5  *   -	GPIO/parport bitbangers.  Provide chipselect() and txrx_word[](),
6  *	expanding the per-word routines from the inline templates below.
7  *
8  *   -	Drivers for controllers resembling bare shift registers.  Provide
9  *	chipselect() and txrx_word[](), with custom setup()/cleanup() methods
10  *	that use your controller's clock and chipselect registers.
11  *
12  * Some hardware works well with requests at spi_transfer scope:
13  *
14  *   -	Drivers leveraging smarter hardware, with fifos or DMA; or for half
15  *	duplex (MicroWire) controllers.  Provide chipselect() and txrx_bufs(),
16  *	and custom setup()/cleanup() methods.
17  */
18 
19 /*
20  * The code that knows what GPIO pins do what should have declared four
21  * functions, ideally as inlines, before including this header:
22  *
23  *  void setsck(struct spi_device *, int is_on);
24  *  void setmosi(struct spi_device *, int is_on);
25  *  int getmiso(struct spi_device *);
26  *  void spidelay(unsigned);
27  *
28  * setsck()'s is_on parameter is a zero/nonzero boolean.
29  *
30  * setmosi()'s is_on parameter is a zero/nonzero boolean.
31  *
32  * getmiso() is required to return 0 or 1 only. Any other value is invalid
33  * and will result in improper operation.
34  *
35  * A non-inlined routine would call bitbang_txrx_*() routines.  The
36  * main loop could easily compile down to a handful of instructions,
37  * especially if the delay is a NOP (to run at peak speed).
38  *
39  * Since this is software, the timings may not be exactly what your board's
40  * chips need ... there may be several reasons you'd need to tweak timings
41  * in these routines, not just to make it faster or slower to match a
42  * particular CPU clock rate.
43  */
44 
45 static inline u32
46 bitbang_txrx_be_cpha0(struct spi_device *spi,
47 		unsigned nsecs, unsigned cpol, unsigned flags,
48 		u32 word, u8 bits)
49 {
50 	/* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
51 
52 	u32 oldbit = (!(word & (1<<(bits-1)))) << 31;
53 	/* clock starts at inactive polarity */
54 	for (word <<= (32 - bits); likely(bits); bits--) {
55 
56 		/* setup MSB (to slave) on trailing edge */
57 		if ((flags & SPI_MASTER_NO_TX) == 0) {
58 			if ((word & (1 << 31)) != oldbit) {
59 				setmosi(spi, word & (1 << 31));
60 				oldbit = word & (1 << 31);
61 			}
62 		}
63 		spidelay(nsecs);	/* T(setup) */
64 
65 		setsck(spi, !cpol);
66 		spidelay(nsecs);
67 
68 		/* sample MSB (from slave) on leading edge */
69 		word <<= 1;
70 		if ((flags & SPI_MASTER_NO_RX) == 0)
71 			word |= getmiso(spi);
72 		setsck(spi, cpol);
73 	}
74 	return word;
75 }
76 
77 static inline u32
78 bitbang_txrx_be_cpha1(struct spi_device *spi,
79 		unsigned nsecs, unsigned cpol, unsigned flags,
80 		u32 word, u8 bits)
81 {
82 	/* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
83 
84 	u32 oldbit = (!(word & (1<<(bits-1)))) << 31;
85 	/* clock starts at inactive polarity */
86 	for (word <<= (32 - bits); likely(bits); bits--) {
87 
88 		/* setup MSB (to slave) on leading edge */
89 		setsck(spi, !cpol);
90 		if ((flags & SPI_MASTER_NO_TX) == 0) {
91 			if ((word & (1 << 31)) != oldbit) {
92 				setmosi(spi, word & (1 << 31));
93 				oldbit = word & (1 << 31);
94 			}
95 		}
96 		spidelay(nsecs); /* T(setup) */
97 
98 		setsck(spi, cpol);
99 		spidelay(nsecs);
100 
101 		/* sample MSB (from slave) on trailing edge */
102 		word <<= 1;
103 		if ((flags & SPI_MASTER_NO_RX) == 0)
104 			word |= getmiso(spi);
105 	}
106 	return word;
107 }
108