[PATCH v3 0/6] spi: Add slave mode support

[PATCH v3 0/6] spi: Add slave mode support

[Geert Uytterhoeven]

	Hi all,

This patch series adds 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 nature 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,
  - ...

Binding an SPI slave handler to the SPI slave device represented by an
SPI slave controller can either be done from DT, or through sysfs.
The latter, which also allows unregistering, is done through a sysfs
virtual file named "slave", cfr. Documentation/spi/spi-summary.

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 system uptime at 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, and this is fully
supported.

>From the point of view of an SPI slave protocol handler, an SPI slave
controller looks almost like an ordinary SPI master controller. The only
exception is that a transfer request will block on the remote SPI
master, and may be cancelled using spi_slave_abort().
Hence "struct spi_master" has become a misnomer.  I'll send an RFC
follow-up patch to fix that.

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, and not yet
implemented.  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.

Changes compared to v2 (highlights only, see individual patches for
more details):
  - In SPI slave mode, represent the (single) slave device again as a
    child of the controller node, which is now optional, and must be
    named "slave" if present,
  - Introduce a separate spi_alloc_slave() function,
  - Replace the SPI_CONTROLLER_IS_SLAVE flag in spi_master.flags by a
    bool in spi_master,
  - Fix cancellation in the spi-sh-msiof driver,
  - Drop "spi: core: Extract of_spi_parse_dt()", which was applied,

Changes compared to v1 (highlights only, see individual patches for
more details):
  - Do not create a child node in SPI slave mode. Instead, add an
    "spi-slave" property, and put the mode properties in the controller
    node.
  - Attach SPI slave controllers to a new "spi_slave" device class,
  - Use a "slave" virtual file in sysfs to (un)register the (single)
    slave device for an SPI slave controller, incl. specifying the slave
    protocol handler,
  - Add cancellation support using spi_master.slave_abort() and
    spi_slave_abort(),
  - Please see the individual patches for more detailed changelog
    information.

Dependencies:
  - Today's spi/for-next,
  - "[PATCH] spi: core: Fix devm_spi_register_master() function name in
    kerneldoc",
  - "[PATCH] spi: core: Replace S_IRUGO permissions by 0444".

For your convenience, I've pushed this series and its dependencies to
the topic/spi-slave-v3 branch of the git repository at
https://git.kernel.org/cgit/linux/kernel/git/geert/renesas-drivers.git

Full test information is also available on the eLinux wiki
(http://elinux.org/Tests:MSIOF-SPI-Slave).

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).

Preparation for all examples below:
    # overlay add a-msiof1-spidev # buggy DT: spidev listed directly in DT
    # overlay add a-msiof2-slave

Example 1:

    # echo spi-slave-time > /sys/class/spi_slave/spi3/slave 
    # 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:

    # echo spi-slave-system-control > /sys/class/spi_slave/spi3/slave 
    # reboot='\x7c\x50'
    # poweroff='\x71\x3f'
    # halt='\x38\x76'
    # suspend='\x1b\x1b'
    # spidev_test -D /dev/spidev2.0 -p $suspend # or $reboot, $poweroff, $halt

Example 3:

    # echo spidev > /sys/class/spi_slave/spi3/slave 
    # spidev_test -D /dev/spidev3.0 -p slave-hello-to-master &
    # spidev_test -D /dev/spidev2.0 -p master-hello-to-slave

Thanks!

Geert Uytterhoeven (5):
  spi: Document DT bindings for SPI controllers in slave mode
  spi: core: Add support for registering SPI slave controllers
  spi: Document SPI slave controller support
  spi: slave: Add SPI slave handler reporting uptime at previous message
  spi: slave: Add SPI slave handler controlling system state

Hisashi Nakamura (1):
  spi: sh-msiof: Add slave mode support

 Documentation/devicetree/bindings/spi/sh-msiof.txt |   2 +
 Documentation/devicetree/bindings/spi/spi-bus.txt  |  76 +++++----
 Documentation/spi/spi-summary                      |  27 +++-
 drivers/spi/Kconfig                                |  26 ++-
 drivers/spi/Makefile                               |   4 +
 drivers/spi/spi-sh-msiof.c                         | 121 ++++++++++----
 drivers/spi/spi-slave-system-control.c             | 154 ++++++++++++++++++
 drivers/spi/spi-slave-time.c                       | 127 +++++++++++++++
 drivers/spi/spi.c                                  | 179 ++++++++++++++++++---
 include/linux/spi/sh_msiof.h                       |   6 +
 include/linux/spi/spi.h                            |  33 +++-
 11 files changed, 655 insertions(+), 100 deletions(-)
 create mode 100644 drivers/spi/spi-slave-system-control.c
 create mode 100644 drivers/spi/spi-slave-time.c

-- 
2.7.4

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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

[PATCH v3 1/6] spi: Document DT bindings for SPI controllers in slave mode

[Geert Uytterhoeven]

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
v3:
  - In SPI slave mode, represent the (single) slave device again as a
    child of the controller node, which is now optional, and must be
    named "slave" if present,
  - Split slave node properties in master mode, slave mode, and common
    properties,

v2:
  - Do not create a child node in SPI slave mode. Instead, add an
    "spi-slave" property, and put the mode properties in the controller
    node.
---
 Documentation/devicetree/bindings/spi/spi-bus.txt | 76 ++++++++++++++---------
 1 file changed, 45 insertions(+), 31 deletions(-)

diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
index 4b1d6e74c744fe96..1f6e86f787efd229 100644
--- a/Documentation/devicetree/bindings/spi/spi-bus.txt
+++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
@@ -1,17 +1,23 @@
 SPI (Serial Peripheral Interface) busses
 
-SPI busses can be described with a node for the SPI master device
-and a set of child nodes for each SPI slave on the bus.  For this
-discussion, it is assumed that the system's SPI controller is in
-SPI master mode.  This binding does not describe SPI controllers
-in slave mode.
+SPI busses can be described with a node for the SPI controller device
+and a set of child nodes for each SPI slave on the bus.  The system's SPI
+controller may be described for use in SPI master mode or in SPI slave mode,
+but not for both at the same time.
 
-The SPI master node requires the following properties:
+The SPI controller node requires the following properties:
+- compatible      - Name of SPI bus controller following generic names
+		    recommended practice.
+
+In master mode, the SPI controller node requires the following additional
+properties:
 - #address-cells  - number of cells required to define a chip select
 		address on the SPI bus.
 - #size-cells     - should be zero.
-- compatible      - name of SPI bus controller following generic names
-		recommended practice.
+
+In slave mode, the SPI controller node requires one additional property:
+- spi-slave       - Empty property.
+
 No other properties are required in the SPI bus node.  It is assumed
 that a driver for an SPI bus device will understand that it is an SPI bus.
 However, the binding does not attempt to define the specific method for
@@ -21,7 +27,7 @@ assumption that board specific platform code will be used to manage
 chip selects.  Individual drivers can define additional properties to
 support describing the chip select layout.
 
-Optional properties:
+Optional properties (master mode only):
 - cs-gpios	  - gpios chip select.
 - num-cs	  - total number of chipselects.
 
@@ -41,28 +47,36 @@ cs1 : native
 cs2 : &gpio1 1 0
 cs3 : &gpio1 2 0
 
-SPI slave nodes must be children of the SPI master node and can
-contain the following properties.
-- reg             - (required) chip select address of device.
-- compatible      - (required) name of SPI device following generic names
-		recommended practice.
-- spi-max-frequency - (required) Maximum SPI clocking speed of device in Hz.
-- spi-cpol        - (optional) Empty property indicating device requires
-		inverse clock polarity (CPOL) mode.
-- spi-cpha        - (optional) Empty property indicating device requires
-		shifted clock phase (CPHA) mode.
-- spi-cs-high     - (optional) Empty property indicating device requires
-		chip select active high.
-- spi-3wire       - (optional) Empty property indicating device requires
-		3-wire mode.
-- spi-lsb-first   - (optional) Empty property indicating device requires
-		LSB first mode.
-- spi-tx-bus-width - (optional) The bus width (number of data wires) that is
-                      used for MOSI. Defaults to 1 if not present.
-- spi-rx-bus-width - (optional) The bus width (number of data wires) that is
-                      used for MISO. Defaults to 1 if not present.
-- spi-rx-delay-us  - (optional) Microsecond delay after a read transfer.
-- spi-tx-delay-us  - (optional) Microsecond delay after a write transfer.
+
+SPI slave nodes must be children of the SPI controller node.
+
+In master mode, one or more slave nodes (up to the number of chip selects) can
+be present.  Required properties are:
+- compatible      - Name of SPI device following generic names recommended
+		    practice.
+- reg             - Chip select address of device.
+- spi-max-frequency - Maximum SPI clocking speed of device in Hz.
+
+In slave mode, the (single) slave node is optional.
+If present, it must be called "slave".  Required properties are:
+- compatible      - Name of SPI device following generic names recommended
+		    practice.
+
+All slave nodes can contain the following optional properties:
+- spi-cpol        - Empty property indicating device requires inverse clock
+		    polarity (CPOL) mode.
+- spi-cpha        - Empty property indicating device requires shifted clock
+		    phase (CPHA) mode.
+- spi-cs-high     - Empty property indicating device requires chip select
+		    active high.
+- spi-3wire       - Empty property indicating device requires 3-wire mode.
+- spi-lsb-first   - Empty property indicating device requires LSB first mode.
+- spi-tx-bus-width - The bus width (number of data wires) that is used for MOSI.
+		    Defaults to 1 if not present.
+- spi-rx-bus-width - The bus width (number of data wires) that is used for MISO.
+		    Defaults to 1 if not present.
+- spi-rx-delay-us - Microsecond delay after a read transfer.
+- spi-tx-delay-us - Microsecond delay after a write transfer.
 
 Some SPI controllers and devices support Dual and Quad SPI transfer mode.
 It allows data in the SPI system to be transferred using 2 wires (DUAL) or 4
-- 
2.7.4

[PATCH v3 2/6] spi: core: Add support for registering SPI slave controllers

[Geert Uytterhoeven]

Add support for registering SPI slave controllers using the existing SPI
master framework:
  - SPI slave controllers must use spi_alloc_slave() instead of
    spi_alloc_master(), and should provide an additional callback
    "slave_abort" to abort an ongoing SPI transfer request,
  - SPI slave controllers are added to a new "spi_slave" device class,
  - SPI slave handlers can be bound to the SPI slave device represented
    by an SPI slave controller using a DT child node named "slave",
  - Alternatively, (un)binding an SPI slave handler to the SPI slave
    device represented by an SPI slave controller can be done by
    (un)registering the slave device through a sysfs virtual file named
    "slave".

>From the point of view of an SPI slave protocol handler, an SPI slave
controller looks almost like an ordinary SPI master controller. The only
exception is that a transfer request will block on the remote SPI
master, and may be cancelled using spi_slave_abort().

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
v3:
  - Introduce a separate spi_alloc_slave() function, which sets up the
    spi_slave_class instead of the spi_master class, to avoid the WARN()
    in device_release(),
  - Wrap spi_alloc_{master,slave}() around __spi_alloc_controller(),
  - Replace the SPI_CONTROLLER_IS_SLAVE flag in spi_master.flags (set by
    the SPI controller driver) by a bool in spi_master (set by
    __spi_alloc_controller()),
  - Revert parsing of slave-specific mode properties in the SPI slave
    controller DT node for the (single) slave device,
  - Register again children from DT or ACPI for SPI slave controllers;
    the single optional slave child node must be called "slave",
  - Let {acpi,of}_spi_notify() also search spi_slave_class devices,
  - Use octal instead of symbolic permissions,
  - s/hander/handler/,

v2:
  - Attach SPI slave controllers to a new "spi_slave" device class,
  - Don't call of_spi_register_master() instead of letting it return
    early for SPI slave controllers,
  - Skip registration of children from DT or ACPI for SPI slave
    controllers,
  - Use a "slave" virtual file in sysfs to (un)register the (single)
    slave device for an SPI slave controller, incl. specifying the slave
    protocol handler,
  - Parse slave-specific mode properties in the SPI slave controller DT
    node for the (single) slave device using of_spi_parse_dt(),
  - Add cancellation support using spi_master.slave_abort() and
    spi_slave_abort(),
  - Rename flag SPI_MASTER_IS_SLAVE to SPI_CONTROLLER_IS_SLAVE,
  - Introduce helper function spi_controller_is_slave(), making it easy
    to leave out SPI slave support where appropriate.
---
 drivers/spi/Kconfig     |  14 +++-
 drivers/spi/Makefile    |   2 +
 drivers/spi/spi.c       | 179 +++++++++++++++++++++++++++++++++++++++++-------
 include/linux/spi/spi.h |  33 +++++++--
 4 files changed, 199 insertions(+), 29 deletions(-)

diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index 1761c9004fc1149e..df8ddec24b5d7e88 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -784,6 +784,18 @@ config SPI_TLE62X0
 
 endif # SPI_MASTER
 
-# (slave support would go here)
+#
+# SLAVE side ... listening to other SPI masters
+#
+
+config SPI_SLAVE
+	bool "SPI slave protocol handlers"
+	help
+	  If your system has a slave-capable SPI controller, you can enable
+	  slave protocol handlers.
+
+if SPI_SLAVE
+
+endif # SPI_SLAVE
 
 endif # SPI
diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
index b375a7a892160b76..e50852c6fcb87d8b 100644
--- a/drivers/spi/Makefile
+++ b/drivers/spi/Makefile
@@ -105,3 +105,5 @@ obj-$(CONFIG_SPI_XILINX)		+= spi-xilinx.o
 obj-$(CONFIG_SPI_XLP)			+= spi-xlp.o
 obj-$(CONFIG_SPI_XTENSA_XTFPGA)		+= spi-xtensa-xtfpga.o
 obj-$(CONFIG_SPI_ZYNQMP_GQSPI)		+= spi-zynqmp-gqspi.o
+
+# SPI slave protocol handlers
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 6f87fec409b5f6fd..c3f6b524b3ceb6c1 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1535,15 +1535,6 @@ static int of_spi_parse_dt(struct spi_master *master, struct spi_device *spi,
 	u32 value;
 	int rc;
 
-	/* Device address */
-	rc = of_property_read_u32(nc, "reg", &value);
-	if (rc) {
-		dev_err(&master->dev, "%s has no valid 'reg' property (%d)\n",
-			nc->full_name, rc);
-		return rc;
-	}
-	spi->chip_select = value;
-
 	/* Mode (clock phase/polarity/etc.) */
 	if (of_find_property(nc, "spi-cpha", NULL))
 		spi->mode |= SPI_CPHA;
@@ -1593,6 +1584,24 @@ static int of_spi_parse_dt(struct spi_master *master, struct spi_device *spi,
 		}
 	}
 
+	if (spi_controller_is_slave(master)) {
+		if (strcmp(nc->name, "slave")) {
+			dev_err(&master->dev, "%s is not called 'slave'\n",
+				nc->full_name);
+			return -EINVAL;
+		}
+		return 0;
+	}
+
+	/* Device address */
+	rc = of_property_read_u32(nc, "reg", &value);
+	if (rc) {
+		dev_err(&master->dev, "%s has no valid 'reg' property (%d)\n",
+			nc->full_name, rc);
+		return rc;
+	}
+	spi->chip_select = value;
+
 	/* Device speed */
 	rc = of_property_read_u32(nc, "spi-max-frequency", &value);
 	if (rc) {
@@ -1658,8 +1667,8 @@ of_register_spi_device(struct spi_master *master, struct device_node *nc)
  * of_register_spi_devices() - Register child devices onto the SPI bus
  * @master:	Pointer to spi_master device
  *
- * Registers an spi_device for each child node of master node which has a 'reg'
- * property.
+ * Registers an spi_device for each child node of controller node which
+ * represents a valid SPI slave.
  */
 static void of_register_spi_devices(struct spi_master *master)
 {
@@ -1828,28 +1837,129 @@ static struct class spi_master_class = {
 	.dev_groups	= spi_master_groups,
 };
 
+#ifdef CONFIG_SPI_SLAVE
+/**
+ * spi_slave_abort - abort the ongoing transfer request on an SPI slave
+ *		     controller
+ * @spi: device used for the current transfer
+ */
+int spi_slave_abort(struct spi_device *spi)
+{
+	struct spi_master *master = spi->master;
+
+	if (spi_controller_is_slave(master) && master->slave_abort)
+		return master->slave_abort(master);
+
+	return -ENOTSUPP;
+}
+EXPORT_SYMBOL_GPL(spi_slave_abort);
+
+static int match_true(struct device *dev, void *data)
+{
+	return 1;
+}
+
+static ssize_t spi_slave_show(struct device *dev,
+			      struct device_attribute *attr, char *buf)
+{
+	struct spi_master *ctlr = container_of(dev, struct spi_master, dev);
+	struct device *child;
+
+	child = device_find_child(&ctlr->dev, NULL, match_true);
+	return sprintf(buf, "%s\n",
+		       child ? to_spi_device(child)->modalias : NULL);
+}
+
+static ssize_t spi_slave_store(struct device *dev,
+			       struct device_attribute *attr, const char *buf,
+			       size_t count)
+{
+	struct spi_master *ctlr = container_of(dev, struct spi_master, dev);
+	struct spi_device *spi;
+	struct device *child;
+	char name[32];
+	int rc;
+
+	rc = sscanf(buf, "%31s", name);
+	if (rc != 1 || !name[0])
+		return -EINVAL;
+
+	child = device_find_child(&ctlr->dev, NULL, match_true);
+	if (child) {
+		/* Remove registered slave */
+		device_unregister(child);
+		put_device(child);
+	}
+
+	if (strcmp(name, "(null)")) {
+		/* Register new slave */
+		spi = spi_alloc_device(ctlr);
+		if (!spi)
+			return -ENOMEM;
+
+		strlcpy(spi->modalias, name, sizeof(spi->modalias));
+
+		rc = spi_add_device(spi);
+		if (rc) {
+			spi_dev_put(spi);
+			return rc;
+		}
+	}
+
+	return count;
+}
+
+static DEVICE_ATTR(slave, 0644, spi_slave_show, spi_slave_store);
+
+static struct attribute *spi_slave_attrs[] = {
+	&dev_attr_slave.attr,
+	NULL,
+};
+
+static const struct attribute_group spi_slave_group = {
+	.attrs = spi_slave_attrs,
+};
+
+static const struct attribute_group *spi_slave_groups[] = {
+	&spi_master_statistics_group,
+	&spi_slave_group,
+	NULL,
+};
+
+static struct class spi_slave_class = {
+	.name		= "spi_slave",
+	.owner		= THIS_MODULE,
+	.dev_release	= spi_master_release,
+	.dev_groups	= spi_slave_groups,
+};
+#else
+extern struct class spi_slave_class;	/* dummy */
+#endif
 
 /**
- * spi_alloc_master - allocate SPI master controller
+ * __spi_alloc_controller - allocate an SPI master or slave controller
  * @dev: the controller, possibly using the platform_bus
  * @size: how much zeroed driver-private data to allocate; the pointer to this
  *	memory is in the driver_data field of the returned device,
  *	accessible with spi_master_get_devdata().
+ * @slave: flag indicating whether to allocate an SPI master (false) or SPI
+ *	slave (true) controller
  * Context: can sleep
  *
- * This call is used only by SPI master controller drivers, which are the
+ * This call is used only by SPI controller drivers, which are the
  * only ones directly touching chip registers.  It's how they allocate
  * an spi_master structure, prior to calling spi_register_master().
  *
  * This must be called from context that can sleep.
  *
- * The caller is responsible for assigning the bus number and initializing
- * the master's methods before calling spi_register_master(); and (after errors
+ * The caller is responsible for assigning the bus number and initializing the
+ * controller's methods before calling spi_register_master(); and (after errors
  * adding the device) calling spi_master_put() to prevent a memory leak.
  *
- * Return: the SPI master structure on success, else NULL.
+ * Return: the SPI controller structure on success, else NULL.
  */
-struct spi_master *spi_alloc_master(struct device *dev, unsigned size)
+struct spi_master *__spi_alloc_controller(struct device *dev,
+					  unsigned int size, bool slave)
 {
 	struct spi_master	*master;
 
@@ -1863,14 +1973,18 @@ struct spi_master *spi_alloc_master(struct device *dev, unsigned size)
 	device_initialize(&master->dev);
 	master->bus_num = -1;
 	master->num_chipselect = 1;
-	master->dev.class = &spi_master_class;
+	master->slave = slave;
+	if (IS_ENABLED(CONFIG_SPI_SLAVE) && slave)
+		master->dev.class = &spi_slave_class;
+	else
+		master->dev.class = &spi_master_class;
 	master->dev.parent = dev;
 	pm_suspend_ignore_children(&master->dev, true);
 	spi_master_set_devdata(master, &master[1]);
 
 	return master;
 }
-EXPORT_SYMBOL_GPL(spi_alloc_master);
+EXPORT_SYMBOL_GPL(__spi_alloc_controller);
 
 #ifdef CONFIG_OF
 static int of_spi_register_master(struct spi_master *master)
@@ -1946,9 +2060,11 @@ int spi_register_master(struct spi_master *master)
 	if (!dev)
 		return -ENODEV;
 
-	status = of_spi_register_master(master);
-	if (status)
-		return status;
+	if (!spi_controller_is_slave(master)) {
+		status = of_spi_register_master(master);
+		if (status)
+			return status;
+	}
 
 	/* even if it's just one always-selected device, there must
 	 * be at least one chipselect
@@ -1985,8 +2101,9 @@ int spi_register_master(struct spi_master *master)
 	status = device_add(&master->dev);
 	if (status < 0)
 		goto done;
-	dev_dbg(dev, "registered master %s%s\n", dev_name(&master->dev),
-			dynamic ? " (dynamic)" : "");
+	dev_dbg(dev, "registered %s %s%s\n",
+			spi_controller_is_slave(master) ? "slave" : "master",
+			dev_name(&master->dev), dynamic ? " (dynamic)" : "");
 
 	/* If we're using a queued driver, start the queue */
 	if (master->transfer)
@@ -3159,6 +3276,9 @@ static struct spi_master *of_find_spi_master_by_node(struct device_node *node)
 
 	dev = class_find_device(&spi_master_class, NULL, node,
 				__spi_of_master_match);
+	if (!dev && IS_ENABLED(CONFIG_SPI_SLAVE))
+		dev = class_find_device(&spi_slave_class, NULL, node,
+					__spi_of_master_match);
 	if (!dev)
 		return NULL;
 
@@ -3240,6 +3360,9 @@ static struct spi_master *acpi_spi_find_master_by_adev(struct acpi_device *adev)
 
 	dev = class_find_device(&spi_master_class, NULL, adev,
 				spi_acpi_master_match);
+	if (!dev && IS_ENABLED(CONFIG_SPI_SLAVE))
+		dev = class_find_device(&spi_slave_class, NULL, adev,
+					spi_acpi_master_match);
 	if (!dev)
 		return NULL;
 
@@ -3312,6 +3435,12 @@ static int __init spi_init(void)
 	if (status < 0)
 		goto err2;
 
+	if (IS_ENABLED(CONFIG_SPI_SLAVE)) {
+		status = class_register(&spi_slave_class);
+		if (status < 0)
+			goto err3;
+	}
+
 	if (IS_ENABLED(CONFIG_OF_DYNAMIC))
 		WARN_ON(of_reconfig_notifier_register(&spi_of_notifier));
 	if (IS_ENABLED(CONFIG_ACPI))
@@ -3319,6 +3448,8 @@ static int __init spi_init(void)
 
 	return 0;
 
+err3:
+	class_unregister(&spi_master_class);
 err2:
 	bus_unregister(&spi_bus_type);
 err1:
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 935bd2854ff19b2a..2c73165a441fa001 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -29,8 +29,8 @@ struct spi_transfer;
 struct spi_flash_read_message;
 
 /*
- * INTERFACES between SPI master-side drivers and SPI infrastructure.
- * (There's no SPI slave support for Linux yet...)
+ * INTERFACES between SPI master-side drivers and SPI slave protocol handlers,
+ * and SPI infrastructure.
  */
 extern struct bus_type spi_bus_type;
 
@@ -374,6 +374,7 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
  * @handle_err: the subsystem calls the driver to handle an error that occurs
  *		in the generic implementation of transfer_one_message().
  * @unprepare_message: undo any work done by prepare_message().
+ * @slave_abort: abort the ongoing transfer request on an SPI slave controller
  * @spi_flash_read: to support spi-controller hardwares that provide
  *                  accelerated interface to read from flash devices.
  * @spi_flash_can_dma: analogous to can_dma() interface, but for
@@ -447,6 +448,8 @@ struct spi_master {
 #define SPI_MASTER_MUST_TX      BIT(4)		/* requires tx */
 #define SPI_MASTER_GPIO_SS      BIT(5)		/* GPIO CS must select slave */
 
+	bool			slave;		/* SPI slave controller */
+
 	/*
 	 * on some hardware transfer / message size may be constrained
 	 * the limit may depend on device transfer settings
@@ -539,6 +542,7 @@ struct spi_master {
 			       struct spi_message *message);
 	int (*unprepare_message)(struct spi_master *master,
 				 struct spi_message *message);
+	int (*slave_abort)(struct spi_master *spi);
 	int (*spi_flash_read)(struct  spi_device *spi,
 			      struct spi_flash_read_message *msg);
 	bool (*spi_flash_can_dma)(struct spi_device *spi,
@@ -595,6 +599,11 @@ static inline void spi_master_put(struct spi_master *master)
 		put_device(&master->dev);
 }
 
+static inline bool spi_controller_is_slave(struct spi_master *ctlr)
+{
+	return IS_ENABLED(CONFIG_SPI_SLAVE) && ctlr->slave;
+}
+
 /* PM calls that need to be issued by the driver */
 extern int spi_master_suspend(struct spi_master *master);
 extern int spi_master_resume(struct spi_master *master);
@@ -605,8 +614,23 @@ extern void spi_finalize_current_message(struct spi_master *master);
 extern void spi_finalize_current_transfer(struct spi_master *master);
 
 /* the spi driver core manages memory for the spi_master classdev */
-extern struct spi_master *
-spi_alloc_master(struct device *host, unsigned size);
+extern struct spi_master *__spi_alloc_controller(struct device *host,
+						 unsigned int size, bool slave);
+
+static inline struct spi_master *spi_alloc_master(struct device *host,
+						  unsigned int size)
+{
+	return __spi_alloc_controller(host, size, false);
+}
+
+static inline struct spi_master *spi_alloc_slave(struct device *host,
+						 unsigned int size)
+{
+	if (!IS_ENABLED(CONFIG_SPI_SLAVE))
+		return NULL;
+
+	return __spi_alloc_controller(host, size, true);
+}
 
 extern int spi_register_master(struct spi_master *master);
 extern int devm_spi_register_master(struct device *dev,
@@ -912,6 +936,7 @@ extern int spi_setup(struct spi_device *spi);
 extern int spi_async(struct spi_device *spi, struct spi_message *message);
 extern int spi_async_locked(struct spi_device *spi,
 			    struct spi_message *message);
+extern int spi_slave_abort(struct spi_device *spi);
 
 static inline size_t
 spi_max_message_size(struct spi_device *spi)
-- 
2.7.4

[PATCH v3 3/6] spi: Document SPI slave controller support

[Geert Uytterhoeven]

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
v3:
  - No changes,

v2:
  - New.
---
 Documentation/spi/spi-summary | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/Documentation/spi/spi-summary b/Documentation/spi/spi-summary
index d1824b399b2d1d79..1721c1b570c32466 100644
--- a/Documentation/spi/spi-summary
+++ b/Documentation/spi/spi-summary
@@ -62,8 +62,8 @@ chips described as using "three wire" signaling: SCK, data, nCSx.
 (That data line is sometimes called MOMI or SISO.)
 
 Microcontrollers often support both master and slave sides of the SPI
-protocol.  This document (and Linux) currently only supports the master
-side of SPI interactions.
+protocol.  This document (and Linux) supports both the master and slave
+sides of SPI interactions.
 
 
 Who uses it?  On what kinds of systems?
@@ -154,9 +154,8 @@ control audio interfaces, present touchscreen sensors as input interfaces,
 or monitor temperature and voltage levels during industrial processing.
 And those might all be sharing the same controller driver.
 
-A "struct spi_device" encapsulates the master-side interface between
-those two types of driver.  At this writing, Linux has no slave side
-programming interface.
+A "struct spi_device" encapsulates the controller-side interface between
+those two types of drivers.
 
 There is a minimal core of SPI programming interfaces, focussing on
 using the driver model to connect controller and protocol drivers using
@@ -177,10 +176,24 @@ 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
-	controller managing bus "B".  All spiB.* devices share one
+	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.
+	Writing the driver name of an SPI slave handler to this file
+	registers the slave device; writing "(null)" unregisters the slave
+	device.
+	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.
+
 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
-- 
2.7.4

[PATCH v3 4/6] spi: sh-msiof: Add slave mode support

[Geert Uytterhoeven]

From: Hisashi Nakamura <hisashi.nakamura.ak@renesas.com>

Add slave mode support to the MSIOF driver, in both PIO and DMA mode.

For now this only supports the transmission of messages with a size
that is known in advance.

Signed-off-by: Hisashi Nakamura <hisashi.nakamura.ak@renesas.com>
Signed-off-by: Hiromitsu Yamasaki <hiromitsu.yamasaki.ym@renesas.com>
[geert: Timeout handling cleanup, spi core integration, cancellation,
	rewording]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
v3:
  - Clear TIF_SIGPENDING when interrupted to fix cancellation,
  - Extract sh_msiof_wait_for_completion(),
  - Add #include <linux/sched/signal.h>,
  - Convert to use spi_alloc_slave(),

v2:
  - Document "spi-slave" property in DT bindings,
  - Use spi_controller_is_slave() helper,
  - Check for "spi-slave" property instead of "slave" child node,
  - Replace SPI_MASTER_IS_SLAVE by SPI_CONTROLLER_IS_SLAVE,
  - Implement cancellation.
---
 Documentation/devicetree/bindings/spi/sh-msiof.txt |   2 +
 drivers/spi/spi-sh-msiof.c                         | 121 +++++++++++++++------
 include/linux/spi/sh_msiof.h                       |   6 +
 3 files changed, 96 insertions(+), 33 deletions(-)

diff --git a/Documentation/devicetree/bindings/spi/sh-msiof.txt b/Documentation/devicetree/bindings/spi/sh-msiof.txt
index dc975064fa273c36..64ee489571c42f88 100644
--- a/Documentation/devicetree/bindings/spi/sh-msiof.txt
+++ b/Documentation/devicetree/bindings/spi/sh-msiof.txt
@@ -38,6 +38,8 @@ Optional properties:
 			 specifiers, one for transmission, and one for
 			 reception.
 - dma-names            : Must contain a list of two DMA names, "tx" and "rx".
+- spi-slave            : Empty property indicating the SPI controller is used
+			 in slave mode.
 - renesas,dtdl         : delay sync signal (setup) in transmit mode.
 			 Must contain one of the following values:
 			 0   (no bit delay)
diff --git a/drivers/spi/spi-sh-msiof.c b/drivers/spi/spi-sh-msiof.c
index 2ce15ca977828668..7c4e8c4f3a9bddfd 100644
--- a/drivers/spi/spi-sh-msiof.c
+++ b/drivers/spi/spi-sh-msiof.c
@@ -2,7 +2,8 @@
  * SuperH MSIOF SPI Master Interface
  *
  * Copyright (c) 2009 Magnus Damm
- * Copyright (C) 2014 Glider bvba
+ * Copyright (C) 2014 Renesas Electronics Corporation
+ * Copyright (C) 2014-2017 Glider bvba
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -26,6 +27,7 @@
 #include <linux/of_device.h>
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
+#include <linux/sched/signal.h>
 #include <linux/sh_dma.h>
 
 #include <linux/spi/sh_msiof.h>
@@ -33,7 +35,6 @@
 
 #include <asm/unaligned.h>
 
-
 struct sh_msiof_chipdata {
 	u16 tx_fifo_size;
 	u16 rx_fifo_size;
@@ -337,7 +338,10 @@ static void sh_msiof_spi_set_pin_regs(struct sh_msiof_spi_priv *p,
 	tmp |= !cs_high << MDR1_SYNCAC_SHIFT;
 	tmp |= lsb_first << MDR1_BITLSB_SHIFT;
 	tmp |= sh_msiof_spi_get_dtdl_and_syncdl(p);
-	sh_msiof_write(p, TMDR1, tmp | MDR1_TRMD | TMDR1_PCON);
+	if (spi_controller_is_slave(p->master))
+		sh_msiof_write(p, TMDR1, tmp | TMDR1_PCON);
+	else
+		sh_msiof_write(p, TMDR1, tmp | MDR1_TRMD | TMDR1_PCON);
 	if (p->master->flags & SPI_MASTER_MUST_TX) {
 		/* These bits are reserved if RX needs TX */
 		tmp &= ~0x0000ffff;
@@ -564,17 +568,19 @@ static int sh_msiof_prepare_message(struct spi_master *master,
 
 static int sh_msiof_spi_start(struct sh_msiof_spi_priv *p, void *rx_buf)
 {
-	int ret;
+	bool slave = spi_controller_is_slave(p->master);
+	int ret = 0;
 
 	/* setup clock and rx/tx signals */
-	ret = sh_msiof_modify_ctr_wait(p, 0, CTR_TSCKE);
+	if (!slave)
+		ret = sh_msiof_modify_ctr_wait(p, 0, CTR_TSCKE);
 	if (rx_buf && !ret)
 		ret = sh_msiof_modify_ctr_wait(p, 0, CTR_RXE);
 	if (!ret)
 		ret = sh_msiof_modify_ctr_wait(p, 0, CTR_TXE);
 
 	/* start by setting frame bit */
-	if (!ret)
+	if (!ret && !slave)
 		ret = sh_msiof_modify_ctr_wait(p, 0, CTR_TFSE);
 
 	return ret;
@@ -582,20 +588,61 @@ static int sh_msiof_spi_start(struct sh_msiof_spi_priv *p, void *rx_buf)
 
 static int sh_msiof_spi_stop(struct sh_msiof_spi_priv *p, void *rx_buf)
 {
-	int ret;
+	bool slave = spi_controller_is_slave(p->master);
+	int ret = 0;
 
 	/* shut down frame, rx/tx and clock signals */
-	ret = sh_msiof_modify_ctr_wait(p, CTR_TFSE, 0);
+	if (!slave)
+		ret = sh_msiof_modify_ctr_wait(p, CTR_TFSE, 0);
 	if (!ret)
 		ret = sh_msiof_modify_ctr_wait(p, CTR_TXE, 0);
 	if (rx_buf && !ret)
 		ret = sh_msiof_modify_ctr_wait(p, CTR_RXE, 0);
-	if (!ret)
+	if (!ret && !slave)
 		ret = sh_msiof_modify_ctr_wait(p, CTR_TSCKE, 0);
 
 	return ret;
 }
 
+static int sh_msiof_slave_abort(struct spi_master *master)
+{
+	struct sh_msiof_spi_priv *p = spi_master_get_devdata(master);
+	unsigned long flags;
+
+	spin_lock_irqsave(&p->done.wait.lock, flags);
+	if (!p->done.done) {
+		wait_queue_t *curr, *next;
+
+		list_for_each_entry_safe(curr, next, &p->done.wait.task_list,
+					 task_list) {
+			signal_wake_up(curr->private, 1);
+			break;
+		}
+	}
+	spin_unlock_irqrestore(&p->done.wait.lock, flags);
+	return 0;
+}
+
+static int sh_msiof_wait_for_completion(struct sh_msiof_spi_priv *p)
+{
+	if (spi_controller_is_slave(p->master)) {
+		int ret = wait_for_completion_interruptible(&p->done);
+
+		if (ret) {
+			dev_dbg(&p->pdev->dev, "interrupted\n");
+			clear_thread_flag(TIF_SIGPENDING);
+			return ret;
+		}
+	} else {
+		if (!wait_for_completion_timeout(&p->done, HZ)) {
+			dev_err(&p->pdev->dev, "timeout\n");
+			return -ETIMEDOUT;
+		}
+	}
+
+	return 0;
+}
+
 static int sh_msiof_spi_txrx_once(struct sh_msiof_spi_priv *p,
 				  void (*tx_fifo)(struct sh_msiof_spi_priv *,
 						  const void *, int, int),
@@ -636,11 +683,9 @@ static int sh_msiof_spi_txrx_once(struct sh_msiof_spi_priv *p,
 	}
 
 	/* wait for tx fifo to be emptied / rx fifo to be filled */
-	if (!wait_for_completion_timeout(&p->done, HZ)) {
-		dev_err(&p->pdev->dev, "PIO timeout\n");
-		ret = -ETIMEDOUT;
+	ret = sh_msiof_wait_for_completion(p);
+	if (ret)
 		goto stop_reset;
-	}
 
 	/* read rx fifo */
 	if (rx_buf)
@@ -746,11 +791,9 @@ static int sh_msiof_dma_once(struct sh_msiof_spi_priv *p, const void *tx,
 	}
 
 	/* wait for tx fifo to be emptied / rx fifo to be filled */
-	if (!wait_for_completion_timeout(&p->done, HZ)) {
-		dev_err(&p->pdev->dev, "DMA timeout\n");
-		ret = -ETIMEDOUT;
+	ret = sh_msiof_wait_for_completion(p);
+	if (ret)
 		goto stop_reset;
-	}
 
 	/* clear status bits */
 	sh_msiof_reset_str(p);
@@ -843,7 +886,8 @@ static int sh_msiof_transfer_one(struct spi_master *master,
 	int ret;
 
 	/* setup clocks (clock already enabled in chipselect()) */
-	sh_msiof_spi_set_clk_regs(p, clk_get_rate(p->clk), t->speed_hz);
+	if (!spi_controller_is_slave(p->master))
+		sh_msiof_spi_set_clk_regs(p, clk_get_rate(p->clk), t->speed_hz);
 
 	while (master->dma_tx && len > 15) {
 		/*
@@ -998,8 +1042,12 @@ static struct sh_msiof_spi_info *sh_msiof_spi_parse_dt(struct device *dev)
 	if (!info)
 		return NULL;
 
+	info->mode = of_property_read_bool(np, "spi-slave") ? MSIOF_SPI_SLAVE
+							    : MSIOF_SPI_MASTER;
+
 	/* Parse the MSIOF properties */
-	of_property_read_u32(np, "num-cs", &num_cs);
+	if (info->mode == MSIOF_SPI_MASTER)
+		of_property_read_u32(np, "num-cs", &num_cs);
 	of_property_read_u32(np, "renesas,tx-fifo-size",
 					&info->tx_fifo_override);
 	of_property_read_u32(np, "renesas,rx-fifo-size",
@@ -1159,34 +1207,40 @@ static int sh_msiof_spi_probe(struct platform_device *pdev)
 	struct spi_master *master;
 	const struct sh_msiof_chipdata *chipdata;
 	const struct of_device_id *of_id;
+	struct sh_msiof_spi_info *info;
 	struct sh_msiof_spi_priv *p;
 	int i;
 	int ret;
 
-	master = spi_alloc_master(&pdev->dev, sizeof(struct sh_msiof_spi_priv));
-	if (master == NULL)
-		return -ENOMEM;
-
-	p = spi_master_get_devdata(master);
-
-	platform_set_drvdata(pdev, p);
-	p->master = master;
-
 	of_id = of_match_device(sh_msiof_match, &pdev->dev);
 	if (of_id) {
 		chipdata = of_id->data;
-		p->info = sh_msiof_spi_parse_dt(&pdev->dev);
+		info = sh_msiof_spi_parse_dt(&pdev->dev);
 	} else {
 		chipdata = (const void *)pdev->id_entry->driver_data;
-		p->info = dev_get_platdata(&pdev->dev);
+		info = dev_get_platdata(&pdev->dev);
 	}
 
-	if (!p->info) {
+	if (!info) {
 		dev_err(&pdev->dev, "failed to obtain device info\n");
-		ret = -ENXIO;
-		goto err1;
+		return -ENXIO;
 	}
 
+	if (info->mode == MSIOF_SPI_SLAVE)
+		master = spi_alloc_slave(&pdev->dev,
+					 sizeof(struct sh_msiof_spi_priv));
+	else
+		master = spi_alloc_master(&pdev->dev,
+					  sizeof(struct sh_msiof_spi_priv));
+	if (master == NULL)
+		return -ENOMEM;
+
+	p = spi_master_get_devdata(master);
+
+	platform_set_drvdata(pdev, p);
+	p->master = master;
+	p->info = info;
+
 	init_completion(&p->done);
 
 	p->clk = devm_clk_get(&pdev->dev, NULL);
@@ -1237,6 +1291,7 @@ static int sh_msiof_spi_probe(struct platform_device *pdev)
 	master->num_chipselect = p->info->num_chipselect;
 	master->setup = sh_msiof_spi_setup;
 	master->prepare_message = sh_msiof_prepare_message;
+	master->slave_abort = sh_msiof_slave_abort;
 	master->bits_per_word_mask = SPI_BPW_RANGE_MASK(8, 32);
 	master->auto_runtime_pm = true;
 	master->transfer_one = sh_msiof_transfer_one;
diff --git a/include/linux/spi/sh_msiof.h b/include/linux/spi/sh_msiof.h
index b087a85f5f72a351..f74b581f242f8c43 100644
--- a/include/linux/spi/sh_msiof.h
+++ b/include/linux/spi/sh_msiof.h
@@ -1,10 +1,16 @@
 #ifndef __SPI_SH_MSIOF_H__
 #define __SPI_SH_MSIOF_H__
 
+enum {
+	MSIOF_SPI_MASTER,
+	MSIOF_SPI_SLAVE,
+};
+
 struct sh_msiof_spi_info {
 	int tx_fifo_override;
 	int rx_fifo_override;
 	u16 num_chipselect;
+	int mode;
 	unsigned int dma_tx_id;
 	unsigned int dma_rx_id;
 	u32 dtdl;
-- 
2.7.4

[PATCH v3 5/6] spi: slave: Add SPI slave handler reporting uptime at previous message

[Geert Uytterhoeven]

Add an example SPI slave handler responding with the uptime at the time
of reception of the last SPI message.

This can be used by an external microcontroller as a dead man's switch.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
v3:
  - Add #include <linux/sched/clock.h>,

v2:
  - Resolve semantic differences in patch description, file header, and
    module description,
  - Use spi_async() instead of spi_read(),
  - Submit the next transfer from the previous transfer's completion
    callback, removing the need for a thread,
  - Let .remove() call spi_slave_abort() to cancel the current ongoing
    transfer, and wait for the completion to terminate,
  - Remove FIXME about hanging kthread_stop().
---
 drivers/spi/Kconfig          |   6 ++
 drivers/spi/Makefile         |   1 +
 drivers/spi/spi-slave-time.c | 127 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 134 insertions(+)
 create mode 100644 drivers/spi/spi-slave-time.c

diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index df8ddec24b5d7e88..ade542c5bfd87e37 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -796,6 +796,12 @@ config SPI_SLAVE
 
 if SPI_SLAVE
 
+config SPI_SLAVE_TIME
+	tristate "SPI slave handler reporting boot up time"
+	help
+	  SPI slave handler responding with the time of reception of the last
+	  SPI message.
+
 endif # SPI_SLAVE
 
 endif # SPI
diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
index e50852c6fcb87d8b..fb078693dbe40da4 100644
--- a/drivers/spi/Makefile
+++ b/drivers/spi/Makefile
@@ -107,3 +107,4 @@ obj-$(CONFIG_SPI_XTENSA_XTFPGA)		+= spi-xtensa-xtfpga.o
 obj-$(CONFIG_SPI_ZYNQMP_GQSPI)		+= spi-zynqmp-gqspi.o
 
 # SPI slave protocol handlers
+obj-$(CONFIG_SPI_SLAVE_TIME)		+= spi-slave-time.o
diff --git a/drivers/spi/spi-slave-time.c b/drivers/spi/spi-slave-time.c
new file mode 100644
index 0000000000000000..c2940f3f18ecd22e
--- /dev/null
+++ b/drivers/spi/spi-slave-time.c
@@ -0,0 +1,127 @@
+/*
+ * SPI slave handler reporting uptime at reception of previous SPI message
+ *
+ * This SPI slave handler sends the time of reception of the last SPI message
+ * as two 32-bit unsigned integers in binary format and in network byte order,
+ * representing the number of seconds and fractional seconds (in microseconds)
+ * since boot up.
+ *
+ * Copyright (C) 2016 Glider bvba
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/completion.h>
+#include <linux/module.h>
+#include <linux/sched/clock.h>
+#include <linux/spi/spi.h>
+
+
+struct spi_slave_time_priv {
+	struct spi_device *spi;
+	struct completion finished;
+	struct spi_transfer xfer;
+	struct spi_message msg;
+	__be32 buf[2];
+};
+
+static int spi_slave_time_submit(struct spi_slave_time_priv *priv);
+
+static void spi_slave_time_complete(void *arg)
+{
+	struct spi_slave_time_priv *priv = arg;
+	int ret;
+
+	ret = priv->msg.status;
+	if (ret)
+		goto terminate;
+
+	ret = spi_slave_time_submit(priv);
+	if (ret)
+		goto terminate;
+
+	return;
+
+terminate:
+	pr_info("%s: Terminating\n", __func__);
+	complete(&priv->finished);
+}
+
+static int spi_slave_time_submit(struct spi_slave_time_priv *priv)
+{
+	u32 rem_ns;
+	int ret;
+	u64 ts;
+
+	ts = local_clock();
+	rem_ns = do_div(ts, 1000000000) / 1000;
+
+	priv->buf[0] = cpu_to_be32(ts);
+	priv->buf[1] = cpu_to_be32(rem_ns);
+
+	spi_message_init_with_transfers(&priv->msg, &priv->xfer, 1);
+
+	priv->msg.complete = spi_slave_time_complete;
+	priv->msg.context = priv;
+
+	ret = spi_async(priv->spi, &priv->msg);
+	if (ret)
+		pr_err("%s: spi_async() failed %d\n", __func__, ret);
+
+	return ret;
+}
+
+static int spi_slave_time_probe(struct spi_device *spi)
+{
+	struct spi_slave_time_priv *priv;
+	int ret;
+
+	/*
+	 * bits_per_word cannot be configured in platform data
+	 */
+	spi->bits_per_word = 8;
+
+	ret = spi_setup(spi);
+	if (ret < 0)
+		return ret;
+
+	priv = devm_kzalloc(&spi->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->spi = spi;
+	init_completion(&priv->finished);
+	priv->xfer.tx_buf = priv->buf;
+	priv->xfer.len = sizeof(priv->buf);
+
+	ret = spi_slave_time_submit(priv);
+	if (ret)
+		return ret;
+
+	spi_set_drvdata(spi, priv);
+	return 0;
+}
+
+static int spi_slave_time_remove(struct spi_device *spi)
+{
+	struct spi_slave_time_priv *priv = spi_get_drvdata(spi);
+
+	spi_slave_abort(spi);
+	wait_for_completion(&priv->finished);
+	return 0;
+}
+
+static struct spi_driver spi_slave_time_driver = {
+	.driver = {
+		.name	= "spi-slave-time",
+	},
+	.probe		= spi_slave_time_probe,
+	.remove		= spi_slave_time_remove,
+};
+module_spi_driver(spi_slave_time_driver);
+
+MODULE_AUTHOR("Geert Uytterhoeven <geert+renesas@glider.be>");
+MODULE_DESCRIPTION("SPI slave reporting uptime at previous SPI message");
+MODULE_LICENSE("GPL v2");
-- 
2.7.4

[PATCH v3 6/6] spi: slave: Add SPI slave handler controlling system state

[Geert Uytterhoeven]

Add an example SPI slave handler to allow remote control of system
reboot, power off, halt, and suspend.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
v3:
  - No changes,

v2:
  - Use spi_async() instead of spi_read(),
  - Submit the next transfer from the previous transfer's completion
    callback, removing the need for a thread,
  - Let .remove() call spi_slave_abort() to cancel the current ongoing
    transfer, and wait for the completion to terminate,
  - Remove FIXME about hanging kthread_stop(),
  - Fix copy-and-pasted module description.
---
 drivers/spi/Kconfig                    |   6 ++
 drivers/spi/Makefile                   |   1 +
 drivers/spi/spi-slave-system-control.c | 154 +++++++++++++++++++++++++++++++++
 3 files changed, 161 insertions(+)
 create mode 100644 drivers/spi/spi-slave-system-control.c

diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index ade542c5bfd87e37..e6d9e329a3801d6d 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -802,6 +802,12 @@ config SPI_SLAVE_TIME
 	  SPI slave handler responding with the time of reception of the last
 	  SPI message.
 
+config SPI_SLAVE_SYSTEM_CONTROL
+	tristate "SPI slave handler controlling system state"
+	help
+	  SPI slave handler to allow remote control of system reboot, power
+	  off, halt, and suspend.
+
 endif # SPI_SLAVE
 
 endif # SPI
diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
index fb078693dbe40da4..1d7923e8c63bc22b 100644
--- a/drivers/spi/Makefile
+++ b/drivers/spi/Makefile
@@ -108,3 +108,4 @@ obj-$(CONFIG_SPI_ZYNQMP_GQSPI)		+= spi-zynqmp-gqspi.o
 
 # SPI slave protocol handlers
 obj-$(CONFIG_SPI_SLAVE_TIME)		+= spi-slave-time.o
+obj-$(CONFIG_SPI_SLAVE_SYSTEM_CONTROL)	+= spi-slave-system-control.o
diff --git a/drivers/spi/spi-slave-system-control.c b/drivers/spi/spi-slave-system-control.c
new file mode 100644
index 0000000000000000..736dd59928cb3bc3
--- /dev/null
+++ b/drivers/spi/spi-slave-system-control.c
@@ -0,0 +1,154 @@
+/*
+ * SPI slave handler controlling system state
+ *
+ * This SPI slave handler allows remote control of system reboot, power off,
+ * halt, and suspend.
+ *
+ * Copyright (C) 2016 Glider bvba
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/completion.h>
+#include <linux/module.h>
+#include <linux/reboot.h>
+#include <linux/suspend.h>
+#include <linux/spi/spi.h>
+
+/*
+ * The numbers are chosen to display something human-readable on two 7-segment
+ * displays connected to two 74HC595 shift registers
+ */
+#define CMD_REBOOT	0x507c	/* rb */
+#define CMD_POWEROFF	0x3f71	/* OF */
+#define CMD_HALT	0x7638	/* HL */
+#define CMD_SUSPEND	0x1b1b	/* ZZ */
+
+struct spi_slave_system_control_priv {
+	struct spi_device *spi;
+	struct completion finished;
+	struct spi_transfer xfer;
+	struct spi_message msg;
+	__le16 cmd;
+};
+
+static
+int spi_slave_system_control_submit(struct spi_slave_system_control_priv *priv);
+
+static void spi_slave_system_control_complete(void *arg)
+{
+	struct spi_slave_system_control_priv *priv = arg;
+	u16 cmd;
+	int ret;
+
+	if (priv->msg.status)
+		goto terminate;
+
+	cmd = le16_to_cpu(priv->cmd);
+	switch (cmd) {
+	case CMD_REBOOT:
+		pr_info("Rebooting system...\n");
+		kernel_restart(NULL);
+
+	case CMD_POWEROFF:
+		pr_info("Powering off system...\n");
+		kernel_power_off();
+		break;
+
+	case CMD_HALT:
+		pr_info("Halting system...\n");
+		kernel_halt();
+		break;
+
+	case CMD_SUSPEND:
+		pr_info("Suspending system...\n");
+		pm_suspend(PM_SUSPEND_MEM);
+		break;
+
+	default:
+		pr_warn("%s: Unknown command 0x%x\n", __func__, cmd);
+		break;
+	}
+
+	ret = spi_slave_system_control_submit(priv);
+	if (ret)
+		goto terminate;
+
+	return;
+
+terminate:
+	pr_info("%s: Terminating\n", __func__);
+	complete(&priv->finished);
+}
+
+static
+int spi_slave_system_control_submit(struct spi_slave_system_control_priv *priv)
+{
+	int ret;
+
+	spi_message_init_with_transfers(&priv->msg, &priv->xfer, 1);
+
+	priv->msg.complete = spi_slave_system_control_complete;
+	priv->msg.context = priv;
+
+	ret = spi_async(priv->spi, &priv->msg);
+	if (ret)
+		pr_err("%s: spi_async() failed %d\n", __func__, ret);
+
+	return ret;
+}
+
+static int spi_slave_system_control_probe(struct spi_device *spi)
+{
+	struct spi_slave_system_control_priv *priv;
+	int ret;
+
+	/*
+	 * bits_per_word cannot be configured in platform data
+	 */
+	spi->bits_per_word = 8;
+
+	ret = spi_setup(spi);
+	if (ret < 0)
+		return ret;
+
+	priv = devm_kzalloc(&spi->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->spi = spi;
+	init_completion(&priv->finished);
+	priv->xfer.rx_buf = &priv->cmd;
+	priv->xfer.len = sizeof(priv->cmd);
+
+	ret = spi_slave_system_control_submit(priv);
+	if (ret)
+		return ret;
+
+	spi_set_drvdata(spi, priv);
+	return 0;
+}
+
+static int spi_slave_system_control_remove(struct spi_device *spi)
+{
+	struct spi_slave_system_control_priv *priv = spi_get_drvdata(spi);
+
+	spi_slave_abort(spi);
+	wait_for_completion(&priv->finished);
+	return 0;
+}
+
+static struct spi_driver spi_slave_system_control_driver = {
+	.driver = {
+		.name	= "spi-slave-system-control",
+	},
+	.probe		= spi_slave_system_control_probe,
+	.remove		= spi_slave_system_control_remove,
+};
+module_spi_driver(spi_slave_system_control_driver);
+
+MODULE_AUTHOR("Geert Uytterhoeven <geert+renesas@glider.be>");
+MODULE_DESCRIPTION("SPI slave handler controlling system state");
+MODULE_LICENSE("GPL v2");
-- 
2.7.4

Re: [PATCH v3 2/6] spi: core: Add support for registering SPI slave controllers

[Geert Uytterhoeven]

On Thu, May 4, 2017 at 7:45 PM, Geert Uytterhoeven
<geert+renesas@glider.be> wrote:
> --- a/include/linux/spi/spi.h
> +++ b/include/linux/spi/spi.h

> @@ -447,6 +448,8 @@ struct spi_master {
>  #define SPI_MASTER_MUST_TX      BIT(4)         /* requires tx */
>  #define SPI_MASTER_GPIO_SS      BIT(5)         /* GPIO CS must select slave */
>
> +       bool                    slave;          /* SPI slave controller */

0day reported I forgot to document this new field in kerneldoc, thanks!
Will fix in v4.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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

Re: [PATCH v3 4/6] spi: sh-msiof: Add slave mode support

[Geert Uytterhoeven]

On Thu, May 4, 2017 at 7:45 PM, Geert Uytterhoeven
<geert+renesas@glider.be> wrote:
> From: Hisashi Nakamura <hisashi.nakamura.ak@renesas.com>
>
> Add slave mode support to the MSIOF driver, in both PIO and DMA mode.
>
> For now this only supports the transmission of messages with a size
> that is known in advance.
>
> Signed-off-by: Hisashi Nakamura <hisashi.nakamura.ak@renesas.com>
> Signed-off-by: Hiromitsu Yamasaki <hiromitsu.yamasaki.ym@renesas.com>
> [geert: Timeout handling cleanup, spi core integration, cancellation,
>         rewording]
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

> index 2ce15ca977828668..7c4e8c4f3a9bddfd 100644
> --- a/drivers/spi/spi-sh-msiof.c
> +++ b/drivers/spi/spi-sh-msiof.c

> +static int sh_msiof_slave_abort(struct spi_master *master)
> +{
> +       struct sh_msiof_spi_priv *p = spi_master_get_devdata(master);
> +       unsigned long flags;
> +
> +       spin_lock_irqsave(&p->done.wait.lock, flags);
> +       if (!p->done.done) {
> +               wait_queue_t *curr, *next;
> +
> +               list_for_each_entry_safe(curr, next, &p->done.wait.task_list,
> +                                        task_list) {
> +                       signal_wake_up(curr->private, 1);

0day reported a build failure in the modular case (thanks!):

    ERROR: "signal_wake_up_state" [drivers/spi/spi-sh-msiof.ko] undefined!

signal_wake_up() is a static inline function calling signal_wake_up_state(),
but the latter is not exported to modules.

I'll bring it up with the scheduler people...

> +                       break;
> +               }
> +       }
> +       spin_unlock_irqrestore(&p->done.wait.lock, flags);
> +       return 0;
> +}

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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

Re: [PATCH v3 1/6] spi: Document DT bindings for SPI controllers in slave mode

[Rob Herring]

On Thu, May 04, 2017 at 07:45:46PM +0200, Geert Uytterhoeven wrote:
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
> v3:
>   - In SPI slave mode, represent the (single) slave device again as a
>     child of the controller node, which is now optional, and must be
>     named "slave" if present,
>   - Split slave node properties in master mode, slave mode, and common
>     properties,
> 
> v2:
>   - Do not create a child node in SPI slave mode. Instead, add an
>     "spi-slave" property, and put the mode properties in the controller
>     node.
> ---
>  Documentation/devicetree/bindings/spi/spi-bus.txt | 76 ++++++++++++++---------
>  1 file changed, 45 insertions(+), 31 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
> index 4b1d6e74c744fe96..1f6e86f787efd229 100644
> --- a/Documentation/devicetree/bindings/spi/spi-bus.txt
> +++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
> @@ -1,17 +1,23 @@
>  SPI (Serial Peripheral Interface) busses
>  
> -SPI busses can be described with a node for the SPI master device
> -and a set of child nodes for each SPI slave on the bus.  For this
> -discussion, it is assumed that the system's SPI controller is in
> -SPI master mode.  This binding does not describe SPI controllers
> -in slave mode.
> +SPI busses can be described with a node for the SPI controller device
> +and a set of child nodes for each SPI slave on the bus.  The system's SPI
> +controller may be described for use in SPI master mode or in SPI slave mode,
> +but not for both at the same time.
>  
> -The SPI master node requires the following properties:
> +The SPI controller node requires the following properties:
> +- compatible      - Name of SPI bus controller following generic names
> +		    recommended practice.
> +
> +In master mode, the SPI controller node requires the following additional
> +properties:
>  - #address-cells  - number of cells required to define a chip select
>  		address on the SPI bus.
>  - #size-cells     - should be zero.
> -- compatible      - name of SPI bus controller following generic names
> -		recommended practice.
> +
> +In slave mode, the SPI controller node requires one additional property:
> +- spi-slave       - Empty property.

Do we still need this if we have a child node called "slave".

Otherwise,

Reviewed-by: Rob Herring <robh@kernel.org>

Re: [PATCH v3 1/6] spi: Document DT bindings for SPI controllers in slave mode

[Geert Uytterhoeven]

Hi Rob,

On Mon, May 8, 2017 at 6:55 PM, Rob Herring <robh@kernel.org> wrote:
> On Thu, May 04, 2017 at 07:45:46PM +0200, Geert Uytterhoeven wrote:
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
>> ---
>> v3:
>>   - In SPI slave mode, represent the (single) slave device again as a
>>     child of the controller node, which is now optional, and must be
>>     named "slave" if present,
>>   - Split slave node properties in master mode, slave mode, and common
>>     properties,
>>
>> v2:
>>   - Do not create a child node in SPI slave mode. Instead, add an
>>     "spi-slave" property, and put the mode properties in the controller
>>     node.

>> --- a/Documentation/devicetree/bindings/spi/spi-bus.txt
>> +++ b/Documentation/devicetree/bindings/spi/spi-bus.txt

>> +In slave mode, the SPI controller node requires one additional property:
>> +- spi-slave       - Empty property.
>
> Do we still need this if we have a child node called "slave".

Yes, as the child node called "slave" is optional.
In that case, configuration of the slave protocol is done through sysfs, but
that is Linux-specific and thus doesn't belong in the DT bindings.

> Otherwise,
>
> Reviewed-by: Rob Herring <robh@kernel.org>

Thank you!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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

Re: [PATCH v3 4/6] spi: sh-msiof: Add slave mode support

[Rob Herring]

On Thu, May 04, 2017 at 07:45:49PM +0200, Geert Uytterhoeven wrote:
> From: Hisashi Nakamura <hisashi.nakamura.ak@renesas.com>
> 
> Add slave mode support to the MSIOF driver, in both PIO and DMA mode.
> 
> For now this only supports the transmission of messages with a size
> that is known in advance.
> 
> Signed-off-by: Hisashi Nakamura <hisashi.nakamura.ak@renesas.com>
> Signed-off-by: Hiromitsu Yamasaki <hiromitsu.yamasaki.ym@renesas.com>
> [geert: Timeout handling cleanup, spi core integration, cancellation,
> 	rewording]
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
> v3:
>   - Clear TIF_SIGPENDING when interrupted to fix cancellation,
>   - Extract sh_msiof_wait_for_completion(),
>   - Add #include <linux/sched/signal.h>,
>   - Convert to use spi_alloc_slave(),
> 
> v2:
>   - Document "spi-slave" property in DT bindings,
>   - Use spi_controller_is_slave() helper,
>   - Check for "spi-slave" property instead of "slave" child node,
>   - Replace SPI_MASTER_IS_SLAVE by SPI_CONTROLLER_IS_SLAVE,
>   - Implement cancellation.
> ---
>  Documentation/devicetree/bindings/spi/sh-msiof.txt |   2 +

Acked-by: Rob Herring <robh@kernel.org>

>  drivers/spi/spi-sh-msiof.c                         | 121 +++++++++++++++------
>  include/linux/spi/sh_msiof.h                       |   6 +
>  3 files changed, 96 insertions(+), 33 deletions(-)

Applied "spi: Document DT bindings for SPI controllers in slave mode" to the spi tree

[Mark Brown]

The patch

   spi: Document DT bindings for SPI controllers in slave mode

has been applied to the spi tree at

   git://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From a8830cb19cfea04edb0381b52fd90eec44986eb9 Mon Sep 17 00:00:00 2001
From: Geert Uytterhoeven <geert+renesas@glider.be>
Date: Mon, 22 May 2017 15:11:40 +0200
Subject: [PATCH] spi: Document DT bindings for SPI controllers in slave mode

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 Documentation/devicetree/bindings/spi/spi-bus.txt | 76 ++++++++++++++---------
 1 file changed, 45 insertions(+), 31 deletions(-)

diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
index 4b1d6e74c744..1f6e86f787ef 100644
--- a/Documentation/devicetree/bindings/spi/spi-bus.txt
+++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
@@ -1,17 +1,23 @@
 SPI (Serial Peripheral Interface) busses
 
-SPI busses can be described with a node for the SPI master device
-and a set of child nodes for each SPI slave on the bus.  For this
-discussion, it is assumed that the system's SPI controller is in
-SPI master mode.  This binding does not describe SPI controllers
-in slave mode.
+SPI busses can be described with a node for the SPI controller device
+and a set of child nodes for each SPI slave on the bus.  The system's SPI
+controller may be described for use in SPI master mode or in SPI slave mode,
+but not for both at the same time.
 
-The SPI master node requires the following properties:
+The SPI controller node requires the following properties:
+- compatible      - Name of SPI bus controller following generic names
+		    recommended practice.
+
+In master mode, the SPI controller node requires the following additional
+properties:
 - #address-cells  - number of cells required to define a chip select
 		address on the SPI bus.
 - #size-cells     - should be zero.
-- compatible      - name of SPI bus controller following generic names
-		recommended practice.
+
+In slave mode, the SPI controller node requires one additional property:
+- spi-slave       - Empty property.
+
 No other properties are required in the SPI bus node.  It is assumed
 that a driver for an SPI bus device will understand that it is an SPI bus.
 However, the binding does not attempt to define the specific method for
@@ -21,7 +27,7 @@ assumption that board specific platform code will be used to manage
 chip selects.  Individual drivers can define additional properties to
 support describing the chip select layout.
 
-Optional properties:
+Optional properties (master mode only):
 - cs-gpios	  - gpios chip select.
 - num-cs	  - total number of chipselects.
 
@@ -41,28 +47,36 @@ cs1 : native
 cs2 : &gpio1 1 0
 cs3 : &gpio1 2 0
 
-SPI slave nodes must be children of the SPI master node and can
-contain the following properties.
-- reg             - (required) chip select address of device.
-- compatible      - (required) name of SPI device following generic names
-		recommended practice.
-- spi-max-frequency - (required) Maximum SPI clocking speed of device in Hz.
-- spi-cpol        - (optional) Empty property indicating device requires
-		inverse clock polarity (CPOL) mode.
-- spi-cpha        - (optional) Empty property indicating device requires
-		shifted clock phase (CPHA) mode.
-- spi-cs-high     - (optional) Empty property indicating device requires
-		chip select active high.
-- spi-3wire       - (optional) Empty property indicating device requires
-		3-wire mode.
-- spi-lsb-first   - (optional) Empty property indicating device requires
-		LSB first mode.
-- spi-tx-bus-width - (optional) The bus width (number of data wires) that is
-                      used for MOSI. Defaults to 1 if not present.
-- spi-rx-bus-width - (optional) The bus width (number of data wires) that is
-                      used for MISO. Defaults to 1 if not present.
-- spi-rx-delay-us  - (optional) Microsecond delay after a read transfer.
-- spi-tx-delay-us  - (optional) Microsecond delay after a write transfer.
+
+SPI slave nodes must be children of the SPI controller node.
+
+In master mode, one or more slave nodes (up to the number of chip selects) can
+be present.  Required properties are:
+- compatible      - Name of SPI device following generic names recommended
+		    practice.
+- reg             - Chip select address of device.
+- spi-max-frequency - Maximum SPI clocking speed of device in Hz.
+
+In slave mode, the (single) slave node is optional.
+If present, it must be called "slave".  Required properties are:
+- compatible      - Name of SPI device following generic names recommended
+		    practice.
+
+All slave nodes can contain the following optional properties:
+- spi-cpol        - Empty property indicating device requires inverse clock
+		    polarity (CPOL) mode.
+- spi-cpha        - Empty property indicating device requires shifted clock
+		    phase (CPHA) mode.
+- spi-cs-high     - Empty property indicating device requires chip select
+		    active high.
+- spi-3wire       - Empty property indicating device requires 3-wire mode.
+- spi-lsb-first   - Empty property indicating device requires LSB first mode.
+- spi-tx-bus-width - The bus width (number of data wires) that is used for MOSI.
+		    Defaults to 1 if not present.
+- spi-rx-bus-width - The bus width (number of data wires) that is used for MISO.
+		    Defaults to 1 if not present.
+- spi-rx-delay-us - Microsecond delay after a read transfer.
+- spi-tx-delay-us - Microsecond delay after a write transfer.
 
 Some SPI controllers and devices support Dual and Quad SPI transfer mode.
 It allows data in the SPI system to be transferred using 2 wires (DUAL) or 4
-- 
2.11.0