From b55f627feeb9d48fdbde3835e18afbc76712e49b Mon Sep 17 00:00:00 2001 From: David Brownell Date: Tue, 30 Jun 2009 11:41:26 -0700 Subject: 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 Cc: "Paulraj, Sandeep" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/spi/spidev.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) (limited to 'drivers') diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c index 5d869c4d3eb..606e7a40a8d 100644 --- a/drivers/spi/spidev.c +++ b/drivers/spi/spidev.c @@ -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; -- cgit v1.2.3-70-g09d2