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>

1 files changed, 9 insertions, 1 deletions

diff --git a/Documentation/spi/spidev_test.c b/Documentation/spi/spidev_test.c
index cf0e3ce0d526..c1a5aad3c75a 100644
--- a/Documentation/spi/spidev_test.c
+++ b/Documentation/spi/spidev_test.c
@@ -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;