Hi all,
This is a first take at adding support for SPI slave controllers to the
Linux SPI subsystem, including:
- DT binding updates for SPI slave support,
- Core support for SPI slave controllers,
- SPI slave support for the Renesas MSIOF device driver (thanks to
Nakamura-san for the initial implementation in the R-Car BSP!),
- Sample SPI slave handlers.
Due to the naure of SPI slave (simultaneous transmit and receive, while
everything runs at the pace of the master), it has hard real-time
requirements: once an SPI transfer is started by the SPI master, a
software SPI slave must have prepared all data to be sent back to the
SPI master. Hence without additional hardware support, an SPI slave
response can never be a reply to a command being simultaneously
transmitted, and SPI slave replies must be received by the SPI master in
a subsequent SPI transfer.
Examples of possible use cases:
- Receiving streams of data in fixed-size messages (e.g. from a
tuner),
- Receiving and transmitting fixed-size messages of data (e.g. network
frames),
- Sending commands, and querying for responses,
- ...
Originally I wanted to implement a simple SPI slave handler that could
interface with an existing Linux SPI slave driver, cfr. Wolfram Sang's
I2C slave mode EEPROM simulator for the i2c subsystem.
Unfortunately I couldn't find any existing driver using an SPI slave
protocol that fulfills the above requirements. The Nordic Semiconductor
nRF8001 BLE controller seems to use a suitable protocol, but I couldn't
find a Linux driver for it. Hence I created two sample SPI slave
protocols and drivers myself:
1. "spi-slave-time" responds with the time of reception of the
last SPI message, which can be used by an external microcontroller
as a dead man's switch.
2. "spi-slave-system-control" allows remote control of system reboot,
power off, halt, and suspend.
For some use cases, using spidev from user space may be a more appropriate
solution than an in-kernel SPI protocol handler.
>From the point of view of an SPI slave protocol handler, an SPI slave
controller looks exactly like an ordinary SPI master controller. Hence
"struct spi_master" may have become a misnomer. For now I didn't bother
fixing that. Should we rename spi_master (and the spi_*master()
functions) to spi_controller? Or create wrappers/defines with "slave"
in their name?
For now, the MSIOF SPI slave driver only supports the transmission of
messages with a size that is known in advance (the hardware can provide
an interrupt when CS is deasserted before, though).
I.e. when the SPI master sends a shorter message, the slave won't
receive it. When the SPI master sends a longer message, the slave will
receive the first part, and the rest will remain in the FIFO.
Handshaking (5-pin SPI, RDY-signal) is optional. An RDY-signal may be
used for one or both of:
1. The SPI slave asserts RDY when it has data available, and wants to
be queried by the SPI master.
-> This can be handled on top, in the SPI slave protocol handler,
using a GPIO.
2. After the SPI master has asserted CS, the SPI slave asserts RDY
when it is ready to accept the transfer.
-> This may need hardware support in the SPI slave controller,
or dynamic GPIO vs. CS pinmuxing.
This patch series applies to both v4.7-rc1 and next-20160622, with the
following 2 patches applied:
1. [PATCH] spi: Improve DT binding documentation,
2. [PATCH] spi: sh-msiof: Remove sh_msiof_spi_priv.chipdata.
For your convenience, I've pushed this series and its dependencies to
the topic/spi-slave-v1 branch of the git repository at
https://git.kernel.org/cgit/linux/kernel/git/geert/renesas-drivers.git
For testing, device tree overlays enabling SPI master and slave
controllers on an expansion I/O connector on r8a7791/koelsch are
available in the topic/renesas-overlays branch of my renesas-drivers git
repository. Please see http://elinux.org/R-Car/DT-Overlays for more
information about using these overlays.
Test wiring on r8a7791/koelsch, between MSIOF1 and MSIOF2 on EXIO
connector A:
- Connect pin 48 (MSIOF1 CS#) to pin 63 (MSIOF2 CS#),
- Connect pin 46 (MSIOF1 SCK) to pin 61 (MSIOF2 SCK),
- Connect pin 54 (MSIOF1 TX/MOSI) to pin 70 (MSIOF2 RX/MOSI),
- Connect pin 56 (MSIOF1 RX/MISO) to pin 68 (MSIOF2 TX/MISO).
Example 1:
# overlay add a-msiof1-spidev
# overlay add a-msiof2-slave-time
# spidev_test -D /dev/spidev2.0 -p dummy-8B
spi mode: 0x0
bits per word: 8
max speed: 500000 Hz (500 KHz)
RX | 00 00 04 6D 00 09 5B BB __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ | ...m..[�
^^^^^ ^^^^^^^^
seconds microseconds
Example 2:
# overlay add a-msiof1-spidev
# overlay add a-msiof2-slave-system-control
# reboot='\x7c\x50'
# poweroff='\x71\x3f'
# halt='\x38\x76'
# suspend='\x1b\x1b'
# spidev_test -D /dev/spidev2.0 -p $suspend # or $reboot, $poweroff, $halt
Thanks for your comments!
Geert Uytterhoeven (5):
[RFC] spi: Document DT bindings for SPI controllers in slave mode
[RFC] spi: core: Add support for registering SPI slave controllers
[RFC] spi: slave: Add SPI slave handler reporting boot up time
[RFC] spi: slave: Add SPI slave handler controlling system state
[RFC] spi: spidev: Allow direct references in DT from SPI slave
controllers
Hisashi Nakamura (1):
[RFC] spi: sh-msiof: Add slave mode support
Documentation/devicetree/bindings/spi/spi-bus.txt | 31 +++--
drivers/spi/Kconfig | 26 ++++-
drivers/spi/Makefile | 4 +
drivers/spi/spi-sh-msiof.c | 52 +++++++--
drivers/spi/spi-slave-system-control.c | 134 ++++++++++++++++++++++
drivers/spi/spi-slave-time.c | 103 +++++++++++++++++
drivers/spi/spi.c | 39 ++++---
drivers/spi/spidev.c | 3 +-
include/linux/spi/sh_msiof.h | 6 +
include/linux/spi/spi.h | 5 +-
10 files changed, 360 insertions(+), 43 deletions(-)
create mode 100644 drivers/spi/spi-slave-system-control.c
create mode 100644 drivers/spi/spi-slave-time.c
--
1.9.1
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
