diff options
Diffstat (limited to 'Documentation/spi/spi-summary.rst')
| -rw-r--r-- | Documentation/spi/spi-summary.rst | 40 |
1 files changed, 16 insertions, 24 deletions
diff --git a/Documentation/spi/spi-summary.rst b/Documentation/spi/spi-summary.rst index f1daffe10d78..33f05901ccf3 100644 --- a/Documentation/spi/spi-summary.rst +++ b/Documentation/spi/spi-summary.rst @@ -105,7 +105,7 @@ find isn't necessarily helpful. The four modes combine two mode bits: - CPHA indicates the clock phase used to sample data; CPHA=0 says sample on the leading edge, CPHA=1 means the trailing edge. - Since the signal needs to stablize before it's sampled, CPHA=0 + Since the signal needs to stabilize before it's sampled, CPHA=0 implies that its data is written half a clock before the first clock edge. The chipselect may have made it become available. @@ -178,10 +178,10 @@ shows up in sysfs in several locations:: /sys/bus/spi/drivers/D ... driver for one or more spi*.* devices - /sys/class/spi_master/spiB ... symlink (or actual device node) to - a logical node which could hold class related state for the SPI - master controller managing bus "B". All spiB.* devices share one - physical SPI bus segment, with SCLK, MOSI, and MISO. + /sys/class/spi_master/spiB ... symlink to a logical node which could hold + class related state for the SPI master controller managing bus "B". + All spiB.* devices share one physical SPI bus segment, with SCLK, + MOSI, and MISO. /sys/devices/.../CTLR/slave ... virtual file for (un)registering the slave device for an SPI slave controller. @@ -191,16 +191,13 @@ shows up in sysfs in several locations:: Reading from this file shows the name of the slave device ("(null)" if not registered). - /sys/class/spi_slave/spiB ... symlink (or actual device node) to - a logical node which could hold class related state for the SPI - slave controller on bus "B". When registered, a single spiB.* - device is present here, possible sharing the physical SPI bus - segment with other SPI slave devices. + /sys/class/spi_slave/spiB ... symlink to a logical node which could hold + class related state for the SPI slave controller on bus "B". When + registered, a single spiB.* device is present here, possible sharing + the physical SPI bus segment with other SPI slave devices. -Note that the actual location of the controller's class state depends -on whether you enabled CONFIG_SYSFS_DEPRECATED or not. At this time, -the only class-specific state is the bus number ("B" in "spiB"), so -those /sys/class entries are only useful to quickly identify busses. +At this time, the only class-specific state is the bus number ("B" in "spiB"), +so those /sys/class entries are only useful to quickly identify busses. How does board-specific init code declare SPI devices? @@ -336,14 +333,6 @@ certainly includes SPI devices hooked up through the card connectors! Non-static Configurations ^^^^^^^^^^^^^^^^^^^^^^^^^ -Developer boards often play by different rules than product boards, and one -example is the potential need to hotplug SPI devices and/or controllers. - -For those cases you might need to use spi_busnum_to_master() to look -up the spi bus master, and will likely need spi_new_device() to provide the -board info based on the board that was hotplugged. Of course, you'd later -call at least spi_unregister_device() when that board is removed. - When Linux includes support for MMC/SD/SDIO/DataFlash cards through SPI, those configurations will also be dynamic. Fortunately, such devices all support basic device identification probes, so they should hotplug normally. @@ -411,8 +400,11 @@ any more such messages. duplex (one pointer is NULL) transfers; + optionally defining short delays after transfers ... using - the spi_transfer.delay_usecs setting (this delay can be the - only protocol effect, if the buffer length is zero); + the spi_transfer.delay.value setting (this delay can be the + only protocol effect, if the buffer length is zero) ... + when specifying this delay the default spi_transfer.delay.unit + is microseconds, however this can be adjusted to clock cycles + or nanoseconds if needed; + whether the chipselect becomes inactive after a transfer and any delay ... by using the spi_transfer.cs_change flag; |