[RFC,v2,2/8] spi: add basic support for SPI offloading

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 289feccca376..54b814cea54c 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2477,6 +2477,28 @@  static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
 	of_spi_parse_dt_cs_delay(nc, &spi->cs_hold, "spi-cs-hold-delay-ns");
 	of_spi_parse_dt_cs_delay(nc, &spi->cs_inactive, "spi-cs-inactive-delay-ns");
 
+	/* Offloads */
+	rc = of_property_count_u32_elems(nc, "spi-offloads");
+	if (rc > 0) {
+		int num_ch = rc;
+
+		if (!ctlr->offload_ops) {
+			dev_err(&ctlr->dev, "SPI controller doesn't support offloading\n");
+			return -EINVAL;
+		}
+
+		for (idx = 0; idx < num_ch; idx++) {
+			of_property_read_u32_index(nc, "spi-offloads", idx, &value);
+
+			rc = ctlr->offload_ops->map_channel(spi, idx, value);
+			if (rc) {
+				dev_err(&ctlr->dev, "Failed to map offload channel %d: %d\n",
+					value, rc);
+				return rc;
+			}
+		}
+	}
+
 	return 0;
 }
 
@@ -3231,6 +3253,11 @@  static int spi_controller_check_ops(struct spi_controller *ctlr)
 		}
 	}
 
+	if (ctlr->offload_ops && !(ctlr->offload_ops->map_channel &&
+				   ctlr->offload_ops->prepare &&
+				   ctlr->offload_ops->unprepare))
+		return -EINVAL;
+
 	return 0;
 }
 
@@ -4708,6 +4735,79 @@  int spi_write_then_read(struct spi_device *spi,
 }
 EXPORT_SYMBOL_GPL(spi_write_then_read);
 
+/**
+ * spi_offload_prepare - prepare offload hardware for a transfer
+ * @spi:	The spi device to use for the transfers.
+ * @id:		Unique identifier for SPI device with more than one offload.
+ * @msg:	The SPI message to use for the offload operation.
+ *
+ * Requests an offload instance with the specified ID and programs it with the
+ * provided message.
+ *
+ * The message must not be pre-optimized (do not call spi_optimize_message() on
+ * the message).
+ *
+ * Calls must be balanced with spi_offload_unprepare().
+ *
+ * Return: 0 on success, else a negative error code.
+ */
+int spi_offload_prepare(struct spi_device *spi, unsigned int id,
+			struct spi_message *msg)
+{
+	struct spi_controller *ctlr = spi->controller;
+	int ret;
+
+	if (!ctlr->offload_ops)
+		return -EOPNOTSUPP;
+
+	msg->offload = true;
+
+	ret = spi_optimize_message(spi, msg);
+	if (ret)
+		return ret;
+
+	mutex_lock(&ctlr->io_mutex);
+	ret = ctlr->offload_ops->prepare(spi, id, msg);
+	mutex_unlock(&ctlr->io_mutex);
+
+	if (ret) {
+		spi_unoptimize_message(msg);
+		msg->offload = false;
+		return ret;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(spi_offload_prepare);
+
+/**
+ * spi_offload_unprepare - releases any resources used by spi_offload_prepare()
+ * @spi:	The same SPI device passed to spi_offload_prepare()
+ * @id:		The same ID device passed to spi_offload_prepare()
+ * @msg:	The same SPI message passed to spi_offload_prepare()
+ *
+ * Callers must ensure that the offload is no longer in use before calling this
+ * function, e.g. no in-progress transfers.
+ */
+void spi_offload_unprepare(struct spi_device *spi, unsigned int id,
+			   struct spi_message *msg)
+{
+	struct spi_controller *ctlr = spi->controller;
+
+	if (!ctlr->offload_ops)
+		return;
+
+	mutex_lock(&ctlr->io_mutex);
+	ctlr->offload_ops->unprepare(spi, id);
+	mutex_unlock(&ctlr->io_mutex);
+
+	msg->offload = false;
+	msg->offload_state = NULL;
+
+	spi_unoptimize_message(msg);
+}
+EXPORT_SYMBOL_GPL(spi_offload_unprepare);
+
 /*-------------------------------------------------------------------------*/
 
 #if IS_ENABLED(CONFIG_OF_DYNAMIC)
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index e8e1e798924f..a8fc16c6bf37 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -31,6 +31,7 @@  struct spi_transfer;
 struct spi_controller_mem_ops;
 struct spi_controller_mem_caps;
 struct spi_message;
+struct spi_controller_offload_ops;
 
 /*
  * INTERFACES between SPI master-side drivers and SPI slave protocol handlers,
@@ -500,6 +501,7 @@  extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 ch
  *	     This field is optional and should only be implemented if the
  *	     controller has native support for memory like operations.
  * @mem_caps: controller capabilities for the handling of memory operations.
+ * @offload_ops: operations for controllers with offload support.
  * @unprepare_message: undo any work done by prepare_message().
  * @slave_abort: abort the ongoing transfer request on an SPI slave controller
  * @target_abort: abort the ongoing transfer request on an SPI target controller
@@ -745,6 +747,9 @@  struct spi_controller {
 	const struct spi_controller_mem_ops *mem_ops;
 	const struct spi_controller_mem_caps *mem_caps;
 
+	/* Operations for controllers with offload support. */
+	const struct spi_controller_offload_ops *offload_ops;
+
 	/* GPIO chip select */
 	struct gpio_desc	**cs_gpiods;
 	bool			use_gpio_descriptors;
@@ -1114,6 +1119,7 @@  struct spi_transfer {
  * @pre_optimized: peripheral driver pre-optimized the message
  * @optimized: the message is in the optimized state
  * @prepared: spi_prepare_message was called for the this message
+ * @offload: message is to be used with offload hardware
  * @status: zero for success, else negative errno
  * @complete: called to report transaction completions
  * @context: the argument to complete() when it's called
@@ -1123,6 +1129,7 @@  struct spi_transfer {
  * @queue: for use by whichever driver currently owns the message
  * @state: for use by whichever driver currently owns the message
  * @opt_state: for use by whichever driver currently owns the message
+ * @offload_state: for use by whichever driver currently owns the message
  * @resources: for resource management when the SPI message is processed
  *
  * A @spi_message is used to execute an atomic sequence of data transfers,
@@ -1151,6 +1158,8 @@  struct spi_message {
 
 	/* spi_prepare_message() was called for this message */
 	bool			prepared;
+	/* spi_offload_prepare() was called on this message */
+	bool			offload;
 
 	/*
 	 * REVISIT: we might want a flag affecting the behavior of the
@@ -1183,6 +1192,11 @@  struct spi_message {
 	 * __spi_optimize_message() and __spi_unoptimize_message().
 	 */
 	void			*opt_state;
+	/*
+	 * Optional state for use by controller driver between calls to
+	 * offload_ops->prepare() and offload_ops->unprepare().
+	 */
+	void			*offload_state;
 
 	/* List of spi_res resources when the SPI message is processed */
 	struct list_head        resources;
@@ -1546,6 +1560,49 @@  static inline ssize_t spi_w8r16be(struct spi_device *spi, u8 cmd)
 
 /*---------------------------------------------------------------------------*/
 
+/*
+ * Offloading support.
+ *
+ * Some SPI controllers support offloading of SPI transfers. Essentially,
+ * this allows the SPI controller to record SPI transfers and then play them
+ * back later in one go via a single trigger.
+ */
+
+/**
+ * struct spi_controller_offload_ops - callbacks for offload support
+ *
+ * Drivers for hardware with offload support need to implement all of these
+ * callbacks.
+ */
+struct spi_controller_offload_ops {
+	/**
+	 * @map_channel: Callback to reserve an offload instance for the given
+	 * SPI device. If a SPI device requires more than one instance, then
+	 * @id is used to differentiate between them. Channels must be unmapped
+	 * in the struct spi_controller::cleanup() callback.
+	 */
+	int (*map_channel)(struct spi_device *spi, unsigned int id,
+			   unsigned int channel);
+	/**
+	 * @prepare: Callback to prepare the offload for the given SPI message.
+	 * @msg and any of its members (including any xfer->tx_buf) is not
+	 * guaranteed to be valid beyond the lifetime of this call.
+	 */
+	int (*prepare)(struct spi_device *spi, unsigned int id,
+		       struct spi_message *msg);
+	/**
+	 * @unprepare: Callback to release any resources used by prepare().
+	 */
+	void (*unprepare)(struct spi_device *spi, unsigned int id);
+};
+
+extern int spi_offload_prepare(struct spi_device *spi, unsigned int id,
+			       struct spi_message *msg);
+extern void spi_offload_unprepare(struct spi_device *spi, unsigned int id,
+				  struct spi_message *msg);
+
+/*---------------------------------------------------------------------------*/
+
 /*
  * INTERFACE between board init code and SPI infrastructure.
  *