SPIGEN(4) FreeBSD Kernel Interfaces Manual SPIGEN(4)
NAME
spigen - SPI generic I/O device driver
SYNOPSIS
To compile this driver into the kernel, place the following lines in your
kernel configuration file:
device spi
device spibus
device spigen
Alternatively, to load the driver as a module at boot time, place the
following line in loader.conf(5):
spigen_load="YES"
DESCRIPTION
The spigen driver provides direct access to a slave device on the SPI
bus. Each instance of a spigen device is associated with a single chip-
select line on the bus, and all I/O performed through that instance is
done with that chip-select line asserted.
SPI data transfers are inherently bi-directional; there are no separate
read and write operations. When commands and data are sent to a device,
data also comes back from the device, although in some cases the data may
not be useful (or even documented or predictable for some devices).
Likewise on a read operation, whatever data is in the buffer at the start
of the operation is sent to (and typically ignored by) the device, with
each outgoing byte then replaced in the buffer by the corresponding
incoming byte. Thus, all buffers passed to the transfer functions are
both input and output buffers.
The spigen driver provides access to the SPI slave device with the
following ioctl(2) calls, defined in <sys/spigenio.h>:
SPIGENIOC_TRANSFER (struct spigen_transfer)
Transfer a command and optional associated data to/from the
device, using the buffers described by the st_command and st_data
fields in the spigen_transfer. Set st_data.iov_len to zero if
there is no data associated with the command.
struct spigen_transfer {
struct iovec st_command;
struct iovec st_data;
};
SPIGENIOC_TRANSFER_MMAPPED (spigen_transfer_mmapped)
Transfer a command and optional associated data to/from the
device. The buffers for the transfer are a previously-mmap'd
region. The length of the command and data within that region
are described by the stm_command_length and stm_data_length
fields of spigen_transfer_mmapped. If stm_data_length is non-
zero, the data appears in the memory region immediately following
the command (that is, at offset stm_command_length from the start
of the mapped region).
struct spigen_transfer_mmapped {
size_t stm_command_length;
size_t stm_data_length;
};
SPIGENIOC_GET_CLOCK_SPEED (uint32_t)
Get the maximum clock speed (bus frequency in Hertz) to be used
when communicating with this slave device.
SPIGENIOC_SET_CLOCK_SPEED (uint32_t)
Set the maximum clock speed (bus frequency in Hertz) to be used
when communicating with this slave device. The setting remains
in effect for subsequent transfers; it is not necessary to reset
this before each transfer. The actual bus frequency may be lower
due to hardware limitations of the SPI bus controller device.
SPIGENIOC_GET_SPI_MODE (uint32_t)
Get the SPI mode (clock polarity and phase) to be used when
communicating with this device.
SPIGENIOC_SET_SPI_MODE (uint32_t)
Set the SPI mode (clock polarity and phase) to be used when
communicating with this device. The setting remains in effect
for subsequent transfers; it is not necessary to reset this
before each transfer.
HINTS CONFIGURATION
On a device.hints(5) based system, such as MIPS, these values are
configurable for spigen:
hint.spigen.%d.at
The spibus the spigen instance is attached to.
hint.spigen.%d.clock
The maximum bus frequency to use when communicating with this
device. Actual bus speed may be lower, depending on the
capabilities of the SPI bus controller hardware.
hint.spigen.%d.cs
The chip-select number to assert when performing I/O for this
device. Set the high bit (1 << 31) to invert the logic level of
the chip select line.
hint.spigen.%d.mode
The SPI mode (0-3) to use when communicating with this device.
FDT CONFIGURATION
On an fdt(4) based system, the spigen device is defined as a slave device
subnode of the SPI bus controller node. All properties documented in the
spibus.txt bindings document can be used with the spigen device. The
most commonly-used ones are documented below.
The following properties are required in the spigen device subnode:
compatible
Must be the string "freebsd,spigen".
reg Chip select address of device.
spi-max-frequency
The maximum bus frequency to use when communicating with this
slave device. Actual bus speed may be lower, depending on the
capabilities of the SPI bus controller hardware.
The following properties are optional for the spigen device subnode:
spi-cpha
Empty property indicating the slave device requires shifted clock
phase (CPHA) mode.
spi-cpol
Empty property indicating the slave device requires inverse clock
polarity (CPOL) mode.
spi-cs-high
Empty property indicating the slave device requires chip select
active high.
FILES
/dev/spigen*
SEE ALSO
fdt(4), device.hints(5), spi(8)
HISTORY
The spigen driver appeared in FreeBSD 11.0. FDT support appeared in
FreeBSD 11.2.
FreeBSD 13.1-RELEASE-p6 August 21, 2020 FreeBSD 13.1-RELEASE-p6
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