Commit b55f627feeb9d48fdbde3835e18afbc76712e49b
Committed by
Linus Torvalds
Linus Torvalds
1 parent
c49568235d
Exists in
master
and in
20 other branches
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>
Showing 4 changed files with 24 additions and 7 deletions Side-by-side Diff
Documentation/spi/spidev_test.c
| ... | ... | @@ -99,11 +99,13 @@ |
| 99 | 99 | { "lsb", 0, 0, 'L' }, |
| 100 | 100 | { "cs-high", 0, 0, 'C' }, |
| 101 | 101 | { "3wire", 0, 0, '3' }, |
| 102 | + { "no-cs", 0, 0, 'N' }, | |
| 103 | + { "ready", 0, 0, 'R' }, | |
| 102 | 104 | { NULL, 0, 0, 0 }, |
| 103 | 105 | }; |
| 104 | 106 | int c; |
| 105 | 107 | |
| 106 | - c = getopt_long(argc, argv, "D:s:d:b:lHOLC3", lopts, NULL); | |
| 108 | + c = getopt_long(argc, argv, "D:s:d:b:lHOLC3NR", lopts, NULL); | |
| 107 | 109 | |
| 108 | 110 | if (c == -1) |
| 109 | 111 | break; |
| ... | ... | @@ -138,6 +140,12 @@ |
| 138 | 140 | break; |
| 139 | 141 | case '3': |
| 140 | 142 | mode |= SPI_3WIRE; |
| 143 | + break; | |
| 144 | + case 'N': | |
| 145 | + mode |= SPI_NO_CS; | |
| 146 | + break; | |
| 147 | + case 'R': | |
| 148 | + mode |= SPI_READY; | |
| 141 | 149 | break; |
| 142 | 150 | default: |
| 143 | 151 | print_usage(argv[0]); |
drivers/spi/spidev.c
| ... | ... | @@ -58,15 +58,20 @@ |
| 58 | 58 | |
| 59 | 59 | |
| 60 | 60 | /* Bit masks for spi_device.mode management. Note that incorrect |
| 61 | - * settings for CS_HIGH and 3WIRE can cause *lots* of trouble for other | |
| 62 | - * devices on a shared bus: CS_HIGH, because this device will be | |
| 63 | - * active when it shouldn't be; 3WIRE, because when active it won't | |
| 64 | - * behave as it should. | |
| 61 | + * settings for some settings can cause *lots* of trouble for other | |
| 62 | + * devices on a shared bus: | |
| 65 | 63 | * |
| 66 | - * REVISIT should changing those two modes be privileged? | |
| 64 | + * - CS_HIGH ... this device will be active when it shouldn't be | |
| 65 | + * - 3WIRE ... when active, it won't behave as it should | |
| 66 | + * - NO_CS ... there will be no explicit message boundaries; this | |
| 67 | + * is completely incompatible with the shared bus model | |
| 68 | + * - READY ... transfers may proceed when they shouldn't. | |
| 69 | + * | |
| 70 | + * REVISIT should changing those flags be privileged? | |
| 67 | 71 | */ |
| 68 | 72 | #define SPI_MODE_MASK (SPI_CPHA | SPI_CPOL | SPI_CS_HIGH \ |
| 69 | - | SPI_LSB_FIRST | SPI_3WIRE | SPI_LOOP) | |
| 73 | + | SPI_LSB_FIRST | SPI_3WIRE | SPI_LOOP \ | |
| 74 | + | SPI_NO_CS | SPI_READY) | |
| 70 | 75 | |
| 71 | 76 | struct spidev_data { |
| 72 | 77 | dev_t devt; |
include/linux/spi/spi.h
| ... | ... | @@ -80,6 +80,8 @@ |
| 80 | 80 | #define SPI_LSB_FIRST 0x08 /* per-word bits-on-wire */ |
| 81 | 81 | #define SPI_3WIRE 0x10 /* SI/SO signals shared */ |
| 82 | 82 | #define SPI_LOOP 0x20 /* loopback mode */ |
| 83 | +#define SPI_NO_CS 0x40 /* 1 dev/bus, no chipselect */ | |
| 84 | +#define SPI_READY 0x80 /* slave pulls low to pause */ | |
| 83 | 85 | u8 bits_per_word; |
| 84 | 86 | int irq; |
| 85 | 87 | void *controller_state; |
include/linux/spi/spidev.h