mfd: Add support for Diolan DLN-2 devices

This patch implements the USB part of the Diolan USB-I2C/SPI/GPIO
Master Adapter DLN-2. Details about the device can be found here:

https://www.diolan.com/i2c/i2c_interface.html.

Information about the USB protocol can be found in the Programmer's
Reference Manual [1], see section 1.7.

Because the hardware has a single transmit endpoint and a single
receive endpoint the communication between the various DLN2 drivers
and the hardware will be muxed/demuxed by this driver.

Each DLN2 module will be identified by the handle field within the DLN2
message header. If a DLN2 module issues multiple commands in parallel
they will be identified by the echo counter field in the message header.

The DLN2 modules can use the dln2_transfer() function to issue a
command and wait for its response. They can also register a callback
that is going to be called when a specific event id is generated by
the device (e.g. GPIO interrupts). The device uses handle 0 for
sending events.

[1] https://www.diolan.com/downloads/dln-api-manual.pdf

Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/Kconfig

@@ -183,6 +183,16 @@ config MFD_DA9063
 	  Additional drivers must be enabled in order to use the functionality
 	  of the device.
 
+config MFD_DLN2
+	tristate "Diolan DLN2 support"
+	select MFD_CORE
+	depends on USB
+	help
+	  This adds support for Diolan USB-I2C/SPI/GPIO Master Adapter
+	  DLN-2. Additional drivers such as I2C_DLN2, GPIO_DLN2,
+	  etc. must be enabled in order to use the functionality of
+	  the device.
+
 config MFD_MC13XXX
 	tristate
 	depends on (SPI_MASTER || I2C)

drivers/mfd/Makefile

@@ -174,6 +174,7 @@ obj-$(CONFIG_MFD_STW481X)	+= stw481x.o
 obj-$(CONFIG_MFD_IPAQ_MICRO)	+= ipaq-micro.o
 obj-$(CONFIG_MFD_MENF21BMC)	+= menf21bmc.o
 obj-$(CONFIG_MFD_HI6421_PMIC)	+= hi6421-pmic-core.o
+obj-$(CONFIG_MFD_DLN2)		+= dln2.o
 
 intel-soc-pmic-objs		:= intel_soc_pmic_core.o intel_soc_pmic_crc.o
 obj-$(CONFIG_INTEL_SOC_PMIC)	+= intel-soc-pmic.o

include/linux/mfd/dln2.h

@@ -0,0 +1,103 @@
+#ifndef __LINUX_USB_DLN2_H
+#define __LINUX_USB_DLN2_H
+
+#define DLN2_CMD(cmd, id)		((cmd) | ((id) << 8))
+
+struct dln2_platform_data {
+	u16 handle;		/* sub-driver handle (internally used only) */
+	u8 port;		/* I2C/SPI port */
+};
+
+/**
+ * dln2_event_cb_t - event callback function signature
+ *
+ * @pdev - the sub-device that registered this callback
+ * @echo - the echo header field received in the message
+ * @data - the data payload
+ * @len  - the data payload length
+ *
+ * The callback function is called in interrupt context and the data payload is
+ * only valid during the call. If the user needs later access of the data, it
+ * must copy it.
+ */
+
+typedef void (*dln2_event_cb_t)(struct platform_device *pdev, u16 echo,
+				const void *data, int len);
+
+/**
+ * dl2n_register_event_cb - register a callback function for an event
+ *
+ * @pdev - the sub-device that registers the callback
+ * @event - the event for which to register a callback
+ * @event_cb - the callback function
+ *
+ * @return 0 in case of success, negative value in case of error
+ */
+int dln2_register_event_cb(struct platform_device *pdev, u16 event,
+			   dln2_event_cb_t event_cb);
+
+/**
+ * dln2_unregister_event_cb - unregister the callback function for an event
+ *
+ * @pdev - the sub-device that registered the callback
+ * @event - the event for which to register a callback
+ */
+void dln2_unregister_event_cb(struct platform_device *pdev, u16 event);
+
+/**
+ * dln2_transfer - issue a DLN2 command and wait for a response and the
+ * associated data
+ *
+ * @pdev - the sub-device which is issuing this transfer
+ * @cmd - the command to be sent to the device
+ * @obuf - the buffer to be sent to the device; it can be NULL if the user
+ *	doesn't need to transmit data with this command
+ * @obuf_len - the size of the buffer to be sent to the device
+ * @ibuf - any data associated with the response will be copied here; it can be
+ *	NULL if the user doesn't need the response data
+ * @ibuf_len - must be initialized to the input buffer size; it will be modified
+ *	to indicate the actual data transferred;
+ *
+ * @return 0 for success, negative value for errors
+ */
+int dln2_transfer(struct platform_device *pdev, u16 cmd,
+		  const void *obuf, unsigned obuf_len,
+		  void *ibuf, unsigned *ibuf_len);
+
+/**
+ * dln2_transfer_rx - variant of @dln2_transfer() where TX buffer is not needed
+ *
+ * @pdev - the sub-device which is issuing this transfer
+ * @cmd - the command to be sent to the device
+ * @ibuf - any data associated with the response will be copied here; it can be
+ *	NULL if the user doesn't need the response data
+ * @ibuf_len - must be initialized to the input buffer size; it will be modified
+ *	to indicate the actual data transferred;
+ *
+ * @return 0 for success, negative value for errors
+ */
+
+static inline int dln2_transfer_rx(struct platform_device *pdev, u16 cmd,
+				   void *ibuf, unsigned *ibuf_len)
+{
+	return dln2_transfer(pdev, cmd, NULL, 0, ibuf, ibuf_len);
+}
+
+/**
+ * dln2_transfer_tx - variant of @dln2_transfer() where RX buffer is not needed
+ *
+ * @pdev - the sub-device which is issuing this transfer
+ * @cmd - the command to be sent to the device
+ * @obuf - the buffer to be sent to the device; it can be NULL if the
+ *	user doesn't need to transmit data with this command
+ * @obuf_len - the size of the buffer to be sent to the device
+ *
+ * @return 0 for success, negative value for errors
+ */
+static inline int dln2_transfer_tx(struct platform_device *pdev, u16 cmd,
+				   const void *obuf, unsigned obuf_len)
+{
+	return dln2_transfer(pdev, cmd, obuf, obuf_len, NULL, NULL);
+}
+
+#endif