Commit b55f627f authored by David Brownell's avatar David Brownell Committed by Linus Torvalds
Browse files

spi: new spi->mode bits 



Add two new spi_device.mode bits to accomodate more protocol options, and
pass them through to usermode drivers:

 * SPI_NO_CS ... a second 3-wire variant, where the chipselect
   line is removed instead of a data line; transfers are still
   full duplex.

   This obviously has STRONG protocol implications since the
   chipselect transitions can't be used to synchronize state
   transitions with the SPI master.

 * SPI_READY ... defines open drain signal that's pulled low
   to pause the clock.  This defines a 5-wire variant (normal
   4-wire SPI plus READY) and two 4-wire variants (READY plus
   each of the 3-wire flavors).

   Such hardware flow control can be a big win.  There are ADC
   converters and flash chips that expose READY signals, but not
   many host controllers support it today.

The spi_bitbang code should be changed to use SPI_NO_CS instead of its
current nonportable hack.  That's a mode most hardware can easily support
(unlike SPI_READY).

Signed-off-by: default avatarDavid Brownell <dbrownell@users.sourceforge.net>
Cc: "Paulraj, Sandeep" <s-paulraj@ti.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c4956823

Documentation/spi/spidev_test.c

+9 −1
Original line number Diff line number Diff line
@@ -99,11 +99,13 @@ void parse_opts(int argc, char *argv[]) 
			{ "lsb",     0, 0, 'L' },

			{ "cs-high", 0, 0, 'C' },

			{ "3wire",   0, 0, '3' },

			{ "no-cs",   0, 0, 'N' },

			{ "ready",   0, 0, 'R' },

			{ NULL, 0, 0, 0 },

		};

		int c;



		c = getopt_long(argc, argv, "D:s:d:b:lHOLC3", lopts, NULL);

		c = getopt_long(argc, argv, "D:s:d:b:lHOLC3NR", lopts, NULL);



		if (c == -1)

			break;
@@ -139,6 +141,12 @@ void parse_opts(int argc, char *argv[]) 
		case '3':

			mode |= SPI_3WIRE;

			break;

		case 'N':

			mode |= SPI_NO_CS;

			break;

		case 'R':

			mode |= SPI_READY;

			break;

		default:

			print_usage(argv[0]);

			break;

drivers/spi/spidev.c

+11 −6
Original line number Diff line number Diff line
@@ -58,15 +58,20 @@ static unsigned long minors[N_SPI_MINORS / BITS_PER_LONG]; 




/* Bit masks for spi_device.mode management.  Note that incorrect

 * settings for CS_HIGH and 3WIRE can cause *lots* of trouble for other

 * devices on a shared bus:  CS_HIGH, because this device will be

 * active when it shouldn't be;  3WIRE, because when active it won't

 * behave as it should.

 * settings for some settings can cause *lots* of trouble for other

 * devices on a shared bus:

 *

 * REVISIT should changing those two modes be privileged?

 *  - CS_HIGH ... this device will be active when it shouldn't be

 *  - 3WIRE ... when active, it won't behave as it should

 *  - NO_CS ... there will be no explicit message boundaries; this

 *	is completely incompatible with the shared bus model

 *  - READY ... transfers may proceed when they shouldn't.

 *

 * REVISIT should changing those flags be privileged?

 */

#define SPI_MODE_MASK		(SPI_CPHA | SPI_CPOL | SPI_CS_HIGH \

				| SPI_LSB_FIRST | SPI_3WIRE | SPI_LOOP)

				| SPI_LSB_FIRST | SPI_3WIRE | SPI_LOOP \

				| SPI_NO_CS | SPI_READY)



struct spidev_data {

	dev_t			devt;

include/linux/spi/spi.h

+2 −0
Original line number Diff line number Diff line
@@ -80,6 +80,8 @@ struct spi_device { 
#define	SPI_LSB_FIRST	0x08			/* per-word bits-on-wire */

#define	SPI_3WIRE	0x10			/* SI/SO signals shared */

#define	SPI_LOOP	0x20			/* loopback mode */

#define	SPI_NO_CS	0x40			/* 1 dev/bus, no chipselect */

#define	SPI_READY	0x80			/* slave pulls low to pause */

	u8			bits_per_word;

	int			irq;

	void			*controller_state;

include/linux/spi/spidev.h

+2 −0
Original line number Diff line number Diff line
@@ -40,6 +40,8 @@ 
#define SPI_LSB_FIRST		0x08

#define SPI_3WIRE		0x10

#define SPI_LOOP		0x20

#define SPI_NO_CS		0x40

#define SPI_READY		0x80



/*---------------------------------------------------------------------------*/

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