xref: /openbmc/u-boot/include/spi.h (revision 20c700f8)
1 /*
2  * Common SPI Interface: Controller-specific definitions
3  *
4  * (C) Copyright 2001
5  * Gerald Van Baren, Custom IDEAS, vanbaren@cideas.com.
6  *
7  * SPDX-License-Identifier:	GPL-2.0+
8  */
9 
10 #ifndef _SPI_H_
11 #define _SPI_H_
12 
13 /* SPI mode flags */
14 #define SPI_CPHA	BIT(0)			/* clock phase */
15 #define SPI_CPOL	BIT(1)			/* clock polarity */
16 #define SPI_MODE_0	(0|0)			/* (original MicroWire) */
17 #define SPI_MODE_1	(0|SPI_CPHA)
18 #define SPI_MODE_2	(SPI_CPOL|0)
19 #define SPI_MODE_3	(SPI_CPOL|SPI_CPHA)
20 #define SPI_CS_HIGH	BIT(2)			/* CS active high */
21 #define SPI_LSB_FIRST	BIT(3)			/* per-word bits-on-wire */
22 #define SPI_3WIRE	BIT(4)			/* SI/SO signals shared */
23 #define SPI_LOOP	BIT(5)			/* loopback mode */
24 #define SPI_SLAVE	BIT(6)			/* slave mode */
25 #define SPI_PREAMBLE	BIT(7)			/* Skip preamble bytes */
26 #define SPI_TX_BYTE	BIT(8)			/* transmit with 1 wire byte */
27 #define SPI_TX_DUAL	BIT(9)			/* transmit with 2 wires */
28 #define SPI_TX_QUAD	BIT(10)			/* transmit with 4 wires */
29 #define SPI_RX_SLOW	BIT(11)			/* receive with 1 wire slow */
30 #define SPI_RX_DUAL	BIT(12)			/* receive with 2 wires */
31 #define SPI_RX_QUAD	BIT(13)			/* receive with 4 wires */
32 
33 /* SPI bus connection options - see enum spi_dual_flash */
34 #define SPI_CONN_DUAL_SHARED		(1 << 0)
35 #define SPI_CONN_DUAL_SEPARATED	(1 << 1)
36 
37 /* Header byte that marks the start of the message */
38 #define SPI_PREAMBLE_END_BYTE	0xec
39 
40 #define SPI_DEFAULT_WORDLEN	8
41 
42 #ifdef CONFIG_DM_SPI
43 /* TODO(sjg@chromium.org): Remove this and use max_hz from struct spi_slave */
44 struct dm_spi_bus {
45 	uint max_hz;
46 };
47 
48 /**
49  * struct dm_spi_platdata - platform data for all SPI slaves
50  *
51  * This describes a SPI slave, a child device of the SPI bus. To obtain this
52  * struct from a spi_slave, use dev_get_parent_platdata(dev) or
53  * dev_get_parent_platdata(slave->dev).
54  *
55  * This data is immuatable. Each time the device is probed, @max_hz and @mode
56  * will be copied to struct spi_slave.
57  *
58  * @cs:		Chip select number (0..n-1)
59  * @max_hz:	Maximum bus speed that this slave can tolerate
60  * @mode:	SPI mode to use for this device (see SPI mode flags)
61  */
62 struct dm_spi_slave_platdata {
63 	unsigned int cs;
64 	uint max_hz;
65 	uint mode;
66 };
67 
68 #endif /* CONFIG_DM_SPI */
69 
70 /**
71  * struct spi_slave - Representation of a SPI slave
72  *
73  * For driver model this is the per-child data used by the SPI bus. It can
74  * be accessed using dev_get_parent_priv() on the slave device. The SPI uclass
75  * sets uip per_child_auto_alloc_size to sizeof(struct spi_slave), and the
76  * driver should not override it. Two platform data fields (max_hz and mode)
77  * are copied into this structure to provide an initial value. This allows
78  * them to be changed, since we should never change platform data in drivers.
79  *
80  * If not using driver model, drivers are expected to extend this with
81  * controller-specific data.
82  *
83  * @dev:		SPI slave device
84  * @max_hz:		Maximum speed for this slave
85  * @speed:		Current bus speed. This is 0 until the bus is first
86  *			claimed.
87  * @bus:		ID of the bus that the slave is attached to. For
88  *			driver model this is the sequence number of the SPI
89  *			bus (bus->seq) so does not need to be stored
90  * @cs:			ID of the chip select connected to the slave.
91  * @mode:		SPI mode to use for this slave (see SPI mode flags)
92  * @wordlen:		Size of SPI word in number of bits
93  * @max_write_size:	If non-zero, the maximum number of bytes which can
94  *			be written at once, excluding command bytes.
95  * @memory_map:		Address of read-only SPI flash access.
96  * @option:		Varies SPI bus options - separate, shared bus.
97  * @flags:		Indication of SPI flags.
98  */
99 struct spi_slave {
100 #ifdef CONFIG_DM_SPI
101 	struct udevice *dev;	/* struct spi_slave is dev->parentdata */
102 	uint max_hz;
103 	uint speed;
104 #else
105 	unsigned int bus;
106 	unsigned int cs;
107 #endif
108 	uint mode;
109 	unsigned int wordlen;
110 	unsigned int max_write_size;
111 	void *memory_map;
112 	u8 option;
113 
114 	u8 flags;
115 #define SPI_XFER_BEGIN		BIT(0)	/* Assert CS before transfer */
116 #define SPI_XFER_END		BIT(1)	/* Deassert CS after transfer */
117 #define SPI_XFER_ONCE		(SPI_XFER_BEGIN | SPI_XFER_END)
118 #define SPI_XFER_MMAP		BIT(2)	/* Memory Mapped start */
119 #define SPI_XFER_MMAP_END	BIT(3)	/* Memory Mapped End */
120 #define SPI_XFER_U_PAGE		BIT(4)
121 };
122 
123 /**
124  * Initialization, must be called once on start up.
125  *
126  * TODO: I don't think we really need this.
127  */
128 void spi_init(void);
129 
130 /**
131  * spi_do_alloc_slave - Allocate a new SPI slave (internal)
132  *
133  * Allocate and zero all fields in the spi slave, and set the bus/chip
134  * select. Use the helper macro spi_alloc_slave() to call this.
135  *
136  * @offset:	Offset of struct spi_slave within slave structure.
137  * @size:	Size of slave structure.
138  * @bus:	Bus ID of the slave chip.
139  * @cs:		Chip select ID of the slave chip on the specified bus.
140  */
141 void *spi_do_alloc_slave(int offset, int size, unsigned int bus,
142 			 unsigned int cs);
143 
144 /**
145  * spi_alloc_slave - Allocate a new SPI slave
146  *
147  * Allocate and zero all fields in the spi slave, and set the bus/chip
148  * select.
149  *
150  * @_struct:	Name of structure to allocate (e.g. struct tegra_spi).
151  *		This structure must contain a member 'struct spi_slave *slave'.
152  * @bus:	Bus ID of the slave chip.
153  * @cs:		Chip select ID of the slave chip on the specified bus.
154  */
155 #define spi_alloc_slave(_struct, bus, cs) \
156 	spi_do_alloc_slave(offsetof(_struct, slave), \
157 			    sizeof(_struct), bus, cs)
158 
159 /**
160  * spi_alloc_slave_base - Allocate a new SPI slave with no private data
161  *
162  * Allocate and zero all fields in the spi slave, and set the bus/chip
163  * select.
164  *
165  * @bus:	Bus ID of the slave chip.
166  * @cs:		Chip select ID of the slave chip on the specified bus.
167  */
168 #define spi_alloc_slave_base(bus, cs) \
169 	spi_do_alloc_slave(0, sizeof(struct spi_slave), bus, cs)
170 
171 /**
172  * Set up communications parameters for a SPI slave.
173  *
174  * This must be called once for each slave. Note that this function
175  * usually doesn't touch any actual hardware, it only initializes the
176  * contents of spi_slave so that the hardware can be easily
177  * initialized later.
178  *
179  * @bus:	Bus ID of the slave chip.
180  * @cs:		Chip select ID of the slave chip on the specified bus.
181  * @max_hz:	Maximum SCK rate in Hz.
182  * @mode:	Clock polarity, clock phase and other parameters.
183  *
184  * Returns: A spi_slave reference that can be used in subsequent SPI
185  * calls, or NULL if one or more of the parameters are not supported.
186  */
187 struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs,
188 		unsigned int max_hz, unsigned int mode);
189 
190 /**
191  * Free any memory associated with a SPI slave.
192  *
193  * @slave:	The SPI slave
194  */
195 void spi_free_slave(struct spi_slave *slave);
196 
197 /**
198  * Claim the bus and prepare it for communication with a given slave.
199  *
200  * This must be called before doing any transfers with a SPI slave. It
201  * will enable and initialize any SPI hardware as necessary, and make
202  * sure that the SCK line is in the correct idle state. It is not
203  * allowed to claim the same bus for several slaves without releasing
204  * the bus in between.
205  *
206  * @slave:	The SPI slave
207  *
208  * Returns: 0 if the bus was claimed successfully, or a negative value
209  * if it wasn't.
210  */
211 int spi_claim_bus(struct spi_slave *slave);
212 
213 /**
214  * Release the SPI bus
215  *
216  * This must be called once for every call to spi_claim_bus() after
217  * all transfers have finished. It may disable any SPI hardware as
218  * appropriate.
219  *
220  * @slave:	The SPI slave
221  */
222 void spi_release_bus(struct spi_slave *slave);
223 
224 /**
225  * Set the word length for SPI transactions
226  *
227  * Set the word length (number of bits per word) for SPI transactions.
228  *
229  * @slave:	The SPI slave
230  * @wordlen:	The number of bits in a word
231  *
232  * Returns: 0 on success, -1 on failure.
233  */
234 int spi_set_wordlen(struct spi_slave *slave, unsigned int wordlen);
235 
236 /**
237  * SPI transfer
238  *
239  * This writes "bitlen" bits out the SPI MOSI port and simultaneously clocks
240  * "bitlen" bits in the SPI MISO port.  That's just the way SPI works.
241  *
242  * The source of the outgoing bits is the "dout" parameter and the
243  * destination of the input bits is the "din" parameter.  Note that "dout"
244  * and "din" can point to the same memory location, in which case the
245  * input data overwrites the output data (since both are buffered by
246  * temporary variables, this is OK).
247  *
248  * spi_xfer() interface:
249  * @slave:	The SPI slave which will be sending/receiving the data.
250  * @bitlen:	How many bits to write and read.
251  * @dout:	Pointer to a string of bits to send out.  The bits are
252  *		held in a byte array and are sent MSB first.
253  * @din:	Pointer to a string of bits that will be filled in.
254  * @flags:	A bitwise combination of SPI_XFER_* flags.
255  *
256  * Returns: 0 on success, not 0 on failure
257  */
258 int  spi_xfer(struct spi_slave *slave, unsigned int bitlen, const void *dout,
259 		void *din, unsigned long flags);
260 
261 /* Copy memory mapped data */
262 void spi_flash_copy_mmap(void *data, void *offset, size_t len);
263 
264 /**
265  * Determine if a SPI chipselect is valid.
266  * This function is provided by the board if the low-level SPI driver
267  * needs it to determine if a given chipselect is actually valid.
268  *
269  * Returns: 1 if bus:cs identifies a valid chip on this board, 0
270  * otherwise.
271  */
272 int spi_cs_is_valid(unsigned int bus, unsigned int cs);
273 
274 #ifndef CONFIG_DM_SPI
275 /**
276  * Activate a SPI chipselect.
277  * This function is provided by the board code when using a driver
278  * that can't control its chipselects automatically (e.g.
279  * common/soft_spi.c). When called, it should activate the chip select
280  * to the device identified by "slave".
281  */
282 void spi_cs_activate(struct spi_slave *slave);
283 
284 /**
285  * Deactivate a SPI chipselect.
286  * This function is provided by the board code when using a driver
287  * that can't control its chipselects automatically (e.g.
288  * common/soft_spi.c). When called, it should deactivate the chip
289  * select to the device identified by "slave".
290  */
291 void spi_cs_deactivate(struct spi_slave *slave);
292 
293 /**
294  * Set transfer speed.
295  * This sets a new speed to be applied for next spi_xfer().
296  * @slave:	The SPI slave
297  * @hz:		The transfer speed
298  */
299 void spi_set_speed(struct spi_slave *slave, uint hz);
300 #endif
301 
302 /**
303  * Write 8 bits, then read 8 bits.
304  * @slave:	The SPI slave we're communicating with
305  * @byte:	Byte to be written
306  *
307  * Returns: The value that was read, or a negative value on error.
308  *
309  * TODO: This function probably shouldn't be inlined.
310  */
311 static inline int spi_w8r8(struct spi_slave *slave, unsigned char byte)
312 {
313 	unsigned char dout[2];
314 	unsigned char din[2];
315 	int ret;
316 
317 	dout[0] = byte;
318 	dout[1] = 0;
319 
320 	ret = spi_xfer(slave, 16, dout, din, SPI_XFER_BEGIN | SPI_XFER_END);
321 	return ret < 0 ? ret : din[1];
322 }
323 
324 /**
325  * Set up a SPI slave for a particular device tree node
326  *
327  * This calls spi_setup_slave() with the correct bus number. Call
328  * spi_free_slave() to free it later.
329  *
330  * @param blob:		Device tree blob
331  * @param slave_node:	Slave node to use
332  * @param spi_node:	SPI peripheral node to use
333  * @return pointer to new spi_slave structure
334  */
335 struct spi_slave *spi_setup_slave_fdt(const void *blob, int slave_node,
336 				      int spi_node);
337 
338 /**
339  * spi_base_setup_slave_fdt() - helper function to set up a SPI slace
340  *
341  * This decodes SPI properties from the slave node to determine the
342  * chip select and SPI parameters.
343  *
344  * @blob:	Device tree blob
345  * @busnum:	Bus number to use
346  * @node:	Device tree node for the SPI bus
347  */
348 struct spi_slave *spi_base_setup_slave_fdt(const void *blob, int busnum,
349 					   int node);
350 
351 #ifdef CONFIG_DM_SPI
352 
353 /**
354  * struct spi_cs_info - Information about a bus chip select
355  *
356  * @dev:	Connected device, or NULL if none
357  */
358 struct spi_cs_info {
359 	struct udevice *dev;
360 };
361 
362 /**
363  * struct struct dm_spi_ops - Driver model SPI operations
364  *
365  * The uclass interface is implemented by all SPI devices which use
366  * driver model.
367  */
368 struct dm_spi_ops {
369 	/**
370 	 * Claim the bus and prepare it for communication.
371 	 *
372 	 * The device provided is the slave device. It's parent controller
373 	 * will be used to provide the communication.
374 	 *
375 	 * This must be called before doing any transfers with a SPI slave. It
376 	 * will enable and initialize any SPI hardware as necessary, and make
377 	 * sure that the SCK line is in the correct idle state. It is not
378 	 * allowed to claim the same bus for several slaves without releasing
379 	 * the bus in between.
380 	 *
381 	 * @dev:	The SPI slave
382 	 *
383 	 * Returns: 0 if the bus was claimed successfully, or a negative value
384 	 * if it wasn't.
385 	 */
386 	int (*claim_bus)(struct udevice *dev);
387 
388 	/**
389 	 * Release the SPI bus
390 	 *
391 	 * This must be called once for every call to spi_claim_bus() after
392 	 * all transfers have finished. It may disable any SPI hardware as
393 	 * appropriate.
394 	 *
395 	 * @dev:	The SPI slave
396 	 */
397 	int (*release_bus)(struct udevice *dev);
398 
399 	/**
400 	 * Set the word length for SPI transactions
401 	 *
402 	 * Set the word length (number of bits per word) for SPI transactions.
403 	 *
404 	 * @bus:	The SPI slave
405 	 * @wordlen:	The number of bits in a word
406 	 *
407 	 * Returns: 0 on success, -ve on failure.
408 	 */
409 	int (*set_wordlen)(struct udevice *dev, unsigned int wordlen);
410 
411 	/**
412 	 * SPI transfer
413 	 *
414 	 * This writes "bitlen" bits out the SPI MOSI port and simultaneously
415 	 * clocks "bitlen" bits in the SPI MISO port.  That's just the way SPI
416 	 * works.
417 	 *
418 	 * The source of the outgoing bits is the "dout" parameter and the
419 	 * destination of the input bits is the "din" parameter.  Note that
420 	 * "dout" and "din" can point to the same memory location, in which
421 	 * case the input data overwrites the output data (since both are
422 	 * buffered by temporary variables, this is OK).
423 	 *
424 	 * spi_xfer() interface:
425 	 * @dev:	The slave device to communicate with
426 	 * @bitlen:	How many bits to write and read.
427 	 * @dout:	Pointer to a string of bits to send out.  The bits are
428 	 *		held in a byte array and are sent MSB first.
429 	 * @din:	Pointer to a string of bits that will be filled in.
430 	 * @flags:	A bitwise combination of SPI_XFER_* flags.
431 	 *
432 	 * Returns: 0 on success, not -1 on failure
433 	 */
434 	int (*xfer)(struct udevice *dev, unsigned int bitlen, const void *dout,
435 		    void *din, unsigned long flags);
436 
437 	/**
438 	 * Set transfer speed.
439 	 * This sets a new speed to be applied for next spi_xfer().
440 	 * @bus:	The SPI bus
441 	 * @hz:		The transfer speed
442 	 * @return 0 if OK, -ve on error
443 	 */
444 	int (*set_speed)(struct udevice *bus, uint hz);
445 
446 	/**
447 	 * Set the SPI mode/flags
448 	 *
449 	 * It is unclear if we want to set speed and mode together instead
450 	 * of separately.
451 	 *
452 	 * @bus:	The SPI bus
453 	 * @mode:	Requested SPI mode (SPI_... flags)
454 	 * @return 0 if OK, -ve on error
455 	 */
456 	int (*set_mode)(struct udevice *bus, uint mode);
457 
458 	/**
459 	 * Get information on a chip select
460 	 *
461 	 * This is only called when the SPI uclass does not know about a
462 	 * chip select, i.e. it has no attached device. It gives the driver
463 	 * a chance to allow activity on that chip select even so.
464 	 *
465 	 * @bus:	The SPI bus
466 	 * @cs:		The chip select (0..n-1)
467 	 * @info:	Returns information about the chip select, if valid.
468 	 *		On entry info->dev is NULL
469 	 * @return 0 if OK (and @info is set up), -ENODEV if the chip select
470 	 *	   is invalid, other -ve value on error
471 	 */
472 	int (*cs_info)(struct udevice *bus, uint cs, struct spi_cs_info *info);
473 };
474 
475 struct dm_spi_emul_ops {
476 	/**
477 	 * SPI transfer
478 	 *
479 	 * This writes "bitlen" bits out the SPI MOSI port and simultaneously
480 	 * clocks "bitlen" bits in the SPI MISO port.  That's just the way SPI
481 	 * works. Here the device is a slave.
482 	 *
483 	 * The source of the outgoing bits is the "dout" parameter and the
484 	 * destination of the input bits is the "din" parameter.  Note that
485 	 * "dout" and "din" can point to the same memory location, in which
486 	 * case the input data overwrites the output data (since both are
487 	 * buffered by temporary variables, this is OK).
488 	 *
489 	 * spi_xfer() interface:
490 	 * @slave:	The SPI slave which will be sending/receiving the data.
491 	 * @bitlen:	How many bits to write and read.
492 	 * @dout:	Pointer to a string of bits sent to the device. The
493 	 *		bits are held in a byte array and are sent MSB first.
494 	 * @din:	Pointer to a string of bits that will be sent back to
495 	 *		the master.
496 	 * @flags:	A bitwise combination of SPI_XFER_* flags.
497 	 *
498 	 * Returns: 0 on success, not -1 on failure
499 	 */
500 	int (*xfer)(struct udevice *slave, unsigned int bitlen,
501 		    const void *dout, void *din, unsigned long flags);
502 };
503 
504 /**
505  * spi_find_bus_and_cs() - Find bus and slave devices by number
506  *
507  * Given a bus number and chip select, this finds the corresponding bus
508  * device and slave device. Neither device is activated by this function,
509  * although they may have been activated previously.
510  *
511  * @busnum:	SPI bus number
512  * @cs:		Chip select to look for
513  * @busp:	Returns bus device
514  * @devp:	Return slave device
515  * @return 0 if found, -ENODEV on error
516  */
517 int spi_find_bus_and_cs(int busnum, int cs, struct udevice **busp,
518 			struct udevice **devp);
519 
520 /**
521  * spi_get_bus_and_cs() - Find and activate bus and slave devices by number
522  *
523  * Given a bus number and chip select, this finds the corresponding bus
524  * device and slave device.
525  *
526  * If no such slave exists, and drv_name is not NULL, then a new slave device
527  * is automatically bound on this chip select.
528  *
529  * Ths new slave device is probed ready for use with the given speed and mode.
530  *
531  * @busnum:	SPI bus number
532  * @cs:		Chip select to look for
533  * @speed:	SPI speed to use for this slave
534  * @mode:	SPI mode to use for this slave
535  * @drv_name:	Name of driver to attach to this chip select
536  * @dev_name:	Name of the new device thus created
537  * @busp:	Returns bus device
538  * @devp:	Return slave device
539  * @return 0 if found, -ve on error
540  */
541 int spi_get_bus_and_cs(int busnum, int cs, int speed, int mode,
542 			const char *drv_name, const char *dev_name,
543 			struct udevice **busp, struct spi_slave **devp);
544 
545 /**
546  * spi_chip_select() - Get the chip select for a slave
547  *
548  * @return the chip select this slave is attached to
549  */
550 int spi_chip_select(struct udevice *slave);
551 
552 /**
553  * spi_find_chip_select() - Find the slave attached to chip select
554  *
555  * @bus:	SPI bus to search
556  * @cs:		Chip select to look for
557  * @devp:	Returns the slave device if found
558  * @return 0 if found, -ENODEV on error
559  */
560 int spi_find_chip_select(struct udevice *bus, int cs, struct udevice **devp);
561 
562 /**
563  * spi_slave_ofdata_to_platdata() - decode standard SPI platform data
564  *
565  * This decodes the speed and mode for a slave from a device tree node
566  *
567  * @blob:	Device tree blob
568  * @node:	Node offset to read from
569  * @plat:	Place to put the decoded information
570  */
571 int spi_slave_ofdata_to_platdata(const void *blob, int node,
572 				 struct dm_spi_slave_platdata *plat);
573 
574 /**
575  * spi_cs_info() - Check information on a chip select
576  *
577  * This checks a particular chip select on a bus to see if it has a device
578  * attached, or is even valid.
579  *
580  * @bus:	The SPI bus
581  * @cs:		The chip select (0..n-1)
582  * @info:	Returns information about the chip select, if valid
583  * @return 0 if OK (and @info is set up), -ENODEV if the chip select
584  *	   is invalid, other -ve value on error
585  */
586 int spi_cs_info(struct udevice *bus, uint cs, struct spi_cs_info *info);
587 
588 struct sandbox_state;
589 
590 /**
591  * sandbox_spi_get_emul() - get an emulator for a SPI slave
592  *
593  * This provides a way to attach an emulated SPI device to a particular SPI
594  * slave, so that xfer() operations on the slave will be handled by the
595  * emulator. If a emulator already exists on that chip select it is returned.
596  * Otherwise one is created.
597  *
598  * @state:	Sandbox state
599  * @bus:	SPI bus requesting the emulator
600  * @slave:	SPI slave device requesting the emulator
601  * @emuip:	Returns pointer to emulator
602  * @return 0 if OK, -ve on error
603  */
604 int sandbox_spi_get_emul(struct sandbox_state *state,
605 			 struct udevice *bus, struct udevice *slave,
606 			 struct udevice **emulp);
607 
608 /**
609  * Claim the bus and prepare it for communication with a given slave.
610  *
611  * This must be called before doing any transfers with a SPI slave. It
612  * will enable and initialize any SPI hardware as necessary, and make
613  * sure that the SCK line is in the correct idle state. It is not
614  * allowed to claim the same bus for several slaves without releasing
615  * the bus in between.
616  *
617  * @dev:	The SPI slave device
618  *
619  * Returns: 0 if the bus was claimed successfully, or a negative value
620  * if it wasn't.
621  */
622 int dm_spi_claim_bus(struct udevice *dev);
623 
624 /**
625  * Release the SPI bus
626  *
627  * This must be called once for every call to dm_spi_claim_bus() after
628  * all transfers have finished. It may disable any SPI hardware as
629  * appropriate.
630  *
631  * @slave:	The SPI slave device
632  */
633 void dm_spi_release_bus(struct udevice *dev);
634 
635 /**
636  * SPI transfer
637  *
638  * This writes "bitlen" bits out the SPI MOSI port and simultaneously clocks
639  * "bitlen" bits in the SPI MISO port.  That's just the way SPI works.
640  *
641  * The source of the outgoing bits is the "dout" parameter and the
642  * destination of the input bits is the "din" parameter.  Note that "dout"
643  * and "din" can point to the same memory location, in which case the
644  * input data overwrites the output data (since both are buffered by
645  * temporary variables, this is OK).
646  *
647  * dm_spi_xfer() interface:
648  * @dev:	The SPI slave device which will be sending/receiving the data.
649  * @bitlen:	How many bits to write and read.
650  * @dout:	Pointer to a string of bits to send out.  The bits are
651  *		held in a byte array and are sent MSB first.
652  * @din:	Pointer to a string of bits that will be filled in.
653  * @flags:	A bitwise combination of SPI_XFER_* flags.
654  *
655  * Returns: 0 on success, not 0 on failure
656  */
657 int dm_spi_xfer(struct udevice *dev, unsigned int bitlen,
658 		const void *dout, void *din, unsigned long flags);
659 
660 /* Access the operations for a SPI device */
661 #define spi_get_ops(dev)	((struct dm_spi_ops *)(dev)->driver->ops)
662 #define spi_emul_get_ops(dev)	((struct dm_spi_emul_ops *)(dev)->driver->ops)
663 #endif /* CONFIG_DM_SPI */
664 
665 #endif	/* _SPI_H_ */
666