i2c: add I2C Address Translator (ATR) support

An ATR is a device that looks similar to an i2c-mux: it has an I2C
slave "upstream" port and N master "downstream" ports, and forwards
transactions from upstream to the appropriate downstream port. But is
is different in that the forwarded transaction has a different slave
address. The address used on the upstream bus is called the "alias"
and is (potentially) different from the physical slave address of the
downstream chip.

Add a helper file (just like i2c-mux.c for a mux or switch) to allow
implementing ATR features in a device driver. The helper takes care or
adapter creation/destruction and translates addresses at each transaction.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>

1 files changed, 82 insertions, 0 deletions

diff --git a/include/linux/i2c-atr.h b/include/linux/i2c-atr.h
new file mode 100644
index 000000000000..e015db668f44
--- /dev/null
+++ b/include/linux/i2c-atr.h
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * drivers/i2c/i2c-atr.h -- I2C Address Translator
+ *
+ * Copyright (c) 2019 Luca Ceresoli <luca@lucaceresoli.net>
+ *
+ * Based on i2c-mux.h
+ */
+
+#ifndef _LINUX_I2C_ATR_H
+#define _LINUX_I2C_ATR_H
+
+#ifdef __KERNEL__
+
+#include <linux/i2c.h>
+#include <linux/mutex.h>
+
+struct i2c_atr;
+
+/**
+ * struct i2c_atr_ops - Callbacks from ATR to the device driver.
+ * @select:        Ask the driver to select a child bus (optional)
+ * @deselect:      Ask the driver to deselect a child bus (optional)
+ * @attach_client: Notify the driver of a new device connected on a child
+ *                 bus. The driver must choose an I2C alias, configure the
+ *                 hardware to use it and return it in `alias_id`.
+ * @detach_client: Notify the driver of a device getting disconnected. The
+ *                 driver must configure the hardware to stop using the
+ *                 alias.
+ *
+ * All these functions return 0 on success, a negative error code otherwise.
+ */
+struct i2c_atr_ops {
+	int  (*select)(struct i2c_atr *atr, u32 chan_id);
+	int  (*deselect)(struct i2c_atr *atr, u32 chan_id);
+	int  (*attach_client)(struct i2c_atr *atr, u32 chan_id,
+			      const struct i2c_board_info *info,
+			      const struct i2c_client *client,
+			      u16 *alias_id);
+	void (*detach_client)(struct i2c_atr *atr, u32 chan_id,
+			      const struct i2c_client *client);
+};
+
+/*
+ * Helper to add I2C ATR features to a device driver.
+ */
+struct i2c_atr {
+	/* private: internal use only */
+
+	struct i2c_adapter *parent;
+	struct device *dev;
+	const struct i2c_atr_ops *ops;
+
+	void *priv;
+
+	struct i2c_algorithm algo;
+	struct mutex lock;
+	int max_adapters;
+
+	struct i2c_adapter *adapter[0];
+};
+
+struct i2c_atr *i2c_atr_new(struct i2c_adapter *parent, struct device *dev,
+			    const struct i2c_atr_ops *ops, int max_adapters);
+void i2c_atr_delete(struct i2c_atr *atr);
+
+static inline void i2c_atr_set_clientdata(struct i2c_atr *atr, void *data)
+{
+	atr->priv = data;
+}
+
+static inline void *i2c_atr_get_clientdata(struct i2c_atr *atr)
+{
+	return atr->priv;
+}
+
+int i2c_atr_add_adapter(struct i2c_atr *atr, u32 chan_id);
+void i2c_atr_del_adapter(struct i2c_atr *atr, u32 chan_id);
+
+#endif /* __KERNEL__ */
+
+#endif /* _LINUX_I2C_ATR_H */