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: David Brownell <dbrownell@users.sourceforge.net>
Cc: "Paulraj, Sandeep" <s-paulraj@ti.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Brownell 2009-06-30 11:41:26 -07:00 committed by Linus Torvalds
parent c49568235d
commit b55f627fee
4 changed files with 24 additions and 7 deletions

View file

@ -99,11 +99,13 @@ void parse_opts(int argc, char *argv[])
{ "lsb", 0, 0, 'L' }, { "lsb", 0, 0, 'L' },
{ "cs-high", 0, 0, 'C' }, { "cs-high", 0, 0, 'C' },
{ "3wire", 0, 0, '3' }, { "3wire", 0, 0, '3' },
{ "no-cs", 0, 0, 'N' },
{ "ready", 0, 0, 'R' },
{ NULL, 0, 0, 0 }, { NULL, 0, 0, 0 },
}; };
int c; 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) if (c == -1)
break; break;
@ -139,6 +141,12 @@ void parse_opts(int argc, char *argv[])
case '3': case '3':
mode |= SPI_3WIRE; mode |= SPI_3WIRE;
break; break;
case 'N':
mode |= SPI_NO_CS;
break;
case 'R':
mode |= SPI_READY;
break;
default: default:
print_usage(argv[0]); print_usage(argv[0]);
break; break;

View file

@ -58,15 +58,20 @@ static unsigned long minors[N_SPI_MINORS / BITS_PER_LONG];
/* Bit masks for spi_device.mode management. Note that incorrect /* Bit masks for spi_device.mode management. Note that incorrect
* settings for CS_HIGH and 3WIRE can cause *lots* of trouble for other * settings for some settings can cause *lots* of trouble for other
* devices on a shared bus: CS_HIGH, because this device will be * devices on a shared bus:
* active when it shouldn't be; 3WIRE, because when active it won't
* behave as it should.
* *
* 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 \ #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 { struct spidev_data {
dev_t devt; dev_t devt;

View file

@ -80,6 +80,8 @@ struct spi_device {
#define SPI_LSB_FIRST 0x08 /* per-word bits-on-wire */ #define SPI_LSB_FIRST 0x08 /* per-word bits-on-wire */
#define SPI_3WIRE 0x10 /* SI/SO signals shared */ #define SPI_3WIRE 0x10 /* SI/SO signals shared */
#define SPI_LOOP 0x20 /* loopback mode */ #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; u8 bits_per_word;
int irq; int irq;
void *controller_state; void *controller_state;

View file

@ -40,6 +40,8 @@
#define SPI_LSB_FIRST 0x08 #define SPI_LSB_FIRST 0x08
#define SPI_3WIRE 0x10 #define SPI_3WIRE 0x10
#define SPI_LOOP 0x20 #define SPI_LOOP 0x20
#define SPI_NO_CS 0x40
#define SPI_READY 0x80
/*---------------------------------------------------------------------------*/ /*---------------------------------------------------------------------------*/