freebsd-skq/share/man/man4/spigen.4

.\"
.\" Copyright (c) 2018 Ian Lepore <ian@freebsd.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd April 7, 2018
.Dt SPIGEN 4
.Os
.Sh NAME
.Nm spigen
.Nd SPI generic I/O device driver
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following lines in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device spi"
.Cd "device spibus"
.Cd "device spigen"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
spigen_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
driver provides direct access to a slave device on the SPI bus.
Each instance of a
.Nm
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.
.Pp
SPI data transfers are inherently bi-directional; there are not 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.
.Pp
The
.Nm
driver provides access to the SPI slave device with the following
.Xr ioctl 2
calls, defined in
.In sys/spigenio.h :
.Bl -tag -width indent
.It Dv SPIGENIOC_TRANSFER Pq Vt "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
.Vt spigen_transfer .
Set
.Vt st_data.iov_len
to zero if there is no data associated with the command.
.Bd -literal
struct spigen_transfer {
	struct iovec st_command;
	struct iovec st_data;
};
.Ed
.It Dv SPIGENIOC_TRANSFER_MMAPPED Pq Vt "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
.Vt stm_command_length
and
.Vt stm_data_length
fields of
.Vt spigen_transfer_mmapped .
If
.Vt stm_data_length
is non-zero, the data appears in the memory region immediately
following the command (that is, at offset
.Vt stm_command_length
from the start of the mapped region).
.Bd -literal
struct spigen_transfer_mmapped {
	size_t stm_command_length;
	size_t stm_data_length;
};
.Ed
.It Dv SPIGENIOC_GET_CLOCK_SPEED Pq Vt uint32_t
Get the maximum clock speed (bus frequency in Hertz) to be used
when communicating with this slave device.
.It Dv SPIGENIOC_SET_CLOCK_SPEED Pq Vt 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 limitiations
of the SPI bus controller device.
.It Dv SPIGENIOC_GET_SPI_MODE Pq Vt uint32_t
Get the SPI mode (clock polarity and phase) to be used
when communicating with this device.
.It Dv SPIGENIOC_SET_SPI_MODE Pq Vt 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.
.El
.Sh HINTS CONFIGURATION
On a 
.Xr device.hints 5
based system, such as
.Li MIPS ,
these values are configurable for
.Nm :
.Bl -tag -width indent
.It Va hint.spigen.%d.at
The spibus the
.Nm
instance is attached to.
.It Va 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.
.It Va 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.
.It Va hint.spigen.%d.mode
The SPI mode (0-3) to use when communicating with this device.
.El
.Sh FDT CONFIGURATION
On an
.Xr 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
.Va spibus.txt
bindings document can be used with the
.Nm
device.
The most commonly-used ones are documented below.
.Pp
The following properties are required in the
.Nm
device subnode:
.Bl -tag -width indent
.It Va compatible
Must be the string "freebsd,spigen".
.It Va reg
Chip select address of device.
.It Va 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.
.El
.Pp
The following properties are optional for the
.Nm
device subnode:
.Bl -tag -width indent
.It Va spi-cpha
Empty property indicating the slave device requires shifted clock
phase (CPHA) mode.
.It Va spi-cpol
Empty property indicating the slave device requires inverse clock
polarity (CPOL) mode.
.It Va spi-cs-high
Empty property indicating the slave device requires chip select active high.
.El
.Sh FILES
.Bl -tag -width -compact
.It Pa /dev/spigen*
.El
.Sh SEE ALSO
.Xr fdt 4 ,
.Xr device.hints 5
.Sh HISTORY
The
.Nm
driver
appeared in
.Fx 11.0 .
FDT support appeared in
.Fx 11.2 .