Unverified Commit b2c98153 authored by Alexandru Ardelean's avatar Alexandru Ardelean Committed by Mark Brown
Browse files

spi: introduce spi_delay struct as "value + unit" & spi_delay_exec() 



There are plenty of delays that have been introduced in SPI core. Most of
them are in micro-seconds, some need to be in nano-seconds, and some in
clock-cycles.

For some of these delays (related to transfers & CS timing) it may make
sense to have a `spi_delay` struct that abstracts these a bit.

The important element of these delays [for unification] seems to be the
`unit` of the delay.
It looks like micro-seconds is good enough for most people, but every-once
in a while, some delays seem to require other units of measurement.

This change adds the `spi_delay` struct & a `spi_delay_exec()` function
that processes a `spi_delay` object/struct to execute the delay.
It's a copy of the `cs_change_delay` mechanism, but without the default
for 10 uS.

The clock-cycle delay unit is a bit special, as it needs to be bound to an
`spi_transfer` object to execute.

Signed-off-by: default avatarAlexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20190926105147.7839-3-alexandru.ardelean@analog.com


Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent 6b3f236a

drivers/spi/spi.c

+51 −0
Original line number Diff line number Diff line
@@ -1106,6 +1106,57 @@ static void _spi_transfer_delay_ns(u32 ns) 
	}

}



static int _spi_delay_to_ns(struct spi_delay *_delay, struct spi_transfer *xfer)

{

	u32 delay = _delay->value;

	u32 unit = _delay->unit;

	u32 hz;



	if (!delay)

		return 0;



	switch (unit) {

	case SPI_DELAY_UNIT_USECS:

		delay *= 1000;

		break;

	case SPI_DELAY_UNIT_NSECS: /* nothing to do here */

		break;

	case SPI_DELAY_UNIT_SCK:

		/* clock cycles need to be obtained from spi_transfer */

		if (!xfer)

			return -EINVAL;

		/* if there is no effective speed know, then approximate

		 * by underestimating with half the requested hz

		 */

		hz = xfer->effective_speed_hz ?: xfer->speed_hz / 2;

		if (!hz)

			return -EINVAL;

		delay *= DIV_ROUND_UP(1000000000, hz);

		break;

	default:

		return -EINVAL;

	}



	return delay;

}



int spi_delay_exec(struct spi_delay *_delay, struct spi_transfer *xfer)

{

	int delay;



	if (!_delay)

		return -EINVAL;



	delay = _spi_delay_to_ns(_delay, xfer);

	if (delay < 0)

		return delay;



	_spi_transfer_delay_ns(delay);



	return 0;

}

EXPORT_SYMBOL_GPL(spi_delay_exec);



static void _spi_transfer_cs_change_delay(struct spi_message *msg,

					  struct spi_transfer *xfer)

{

include/linux/spi/spi.h

+15 −3
Original line number Diff line number Diff line
@@ -90,6 +90,21 @@ void spi_statistics_add_transfer_stats(struct spi_statistics *stats, 
#define SPI_STATISTICS_INCREMENT_FIELD(stats, field)	\

	SPI_STATISTICS_ADD_TO_FIELD(stats, field, 1)



/**

 * struct spi_delay - SPI delay information

 * @value: Value for the delay

 * @unit: Unit for the delay

 */

struct spi_delay {

#define SPI_DELAY_UNIT_USECS	0

#define SPI_DELAY_UNIT_NSECS	1

#define SPI_DELAY_UNIT_SCK	2

	u16	value;

	u8	unit;

};



extern int spi_delay_exec(struct spi_delay *_delay, struct spi_transfer *xfer);



/**

 * struct spi_device - Controller side proxy for an SPI slave device

 * @dev: Driver model representation of the device.
@@ -887,9 +902,6 @@ struct spi_transfer { 
	u16		delay_usecs;

	u16		cs_change_delay;

	u8		cs_change_delay_unit;

#define SPI_DELAY_UNIT_USECS	0

#define SPI_DELAY_UNIT_NSECS	1

#define SPI_DELAY_UNIT_SCK	2

	u32		speed_hz;

	u16		word_delay;

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