[PATCH v4 2/6] spi: core: Add support for registering SPI slave controllers

[Geert Uytterhoeven <geert+renesas@xxxxxxxxx>]

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@xxxxxxxxx>
---
v4:
  - Add missing kerneldoc for spi_master.slave,

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 |  35 ++++++++--
 4 files changed, 201 insertions(+), 29 deletions(-)

diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index 097883362036416f..f21499b1f71ab7c3 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -785,6 +785,18 @@ 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..0a78745e5766451e 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;
 
@@ -311,6 +311,7 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
  * @min_speed_hz: Lowest supported transfer speed
  * @max_speed_hz: Highest supported transfer speed
  * @flags: other constraints relevant to this driver
+ * @slave: indicates that this is an SPI slave controller
  * @max_transfer_size: function that returns the max transfer size for
  *	a &spi_device; may be %NULL, so the default %SIZE_MAX will be used.
  * @max_message_size: function that returns the max message size for
@@ -374,6 +375,7 @@ 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 +449,9 @@ struct spi_master {
 #define SPI_MASTER_MUST_TX      BIT(4)		/* requires tx */
 #define SPI_MASTER_GPIO_SS      BIT(5)		/* GPIO CS must select slave */
 
+	/* flag indicating this is an SPI slave controller */
+	bool			slave;
+
 	/*
 	 * on some hardware transfer / message size may be constrained
 	 * the limit may depend on device transfer settings
@@ -539,6 +544,7 @@ 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 +601,11 @@ 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 +616,23 @@ 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 +938,7 @@ 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

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