spi: core: Add support for registering SPI slave controllers

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>
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 31 insertions, 4 deletions

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 935bd28..0a78745 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)