[PATCH i2c-next 1/1] i2c: mux: Add register map based mux driver

[Vadim Pasternak <vadimp@nvidia.com>]

Add 'regmap' mux driver to allow virtual bus switching by setting a
single selector register.
The 'regmap' is supposed to be passed to driver within a platform data
by parent platform driver.

Motivation is to support indirect access to register space where
selector register is located.
For example, Lattice FPGA LFD2NX-40 device, being connected through
PCIe bus provides SPI or LPC bus logic through PCIe-to-SPI or
PCIe-to-LPC bridging. Thus, FPGA operates a as host controller and
some slave devices can be connected to it. For example:
- CPU (PCIe) -> FPGA (PCIe-to-SPI bridge) -> CPLD or another FPGA.
- CPU (PCIe) -> FPGA (PCIe-to-LPC bridge) -> CPLD or another FPGA.
Where 1-st FPGA connected to PCIe is located on carrier board, while
2-nd programming logic device is located on some switch board and
cannot be connected to CPU PCIe root complex.

In case mux selector register is located within the 2-nd device, SPI or
LPC transactions are sent indirectly through pre-defined protocol.

To support such protocol reg_read()/reg_write() callbacks are provided
to 'regmap' object and these callback implements required indirect
access.

For example, flow in reg_write() will be as following:
- Verify there is no pending transactions.
- Set address in PCIe register space.
- Set data to be written in PCIe register space.
- Activate write operation in PCIe register space.
- LPC or SPI write transaction is performed.

Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
---
 drivers/i2c/muxes/Kconfig                    |  12 ++
 drivers/i2c/muxes/Makefile                   |   1 +
 drivers/i2c/muxes/i2c-mux-regmap.c           | 123 +++++++++++++++++++
 include/linux/platform_data/i2c-mux-regmap.h |  34 +++++
 4 files changed, 170 insertions(+)
 create mode 100644 drivers/i2c/muxes/i2c-mux-regmap.c
 create mode 100644 include/linux/platform_data/i2c-mux-regmap.h

diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
index ea838dbae32e..af2dbacdda57 100644
--- a/drivers/i2c/muxes/Kconfig
+++ b/drivers/i2c/muxes/Kconfig
@@ -119,4 +119,16 @@ config I2C_MUX_MLXCPLD
 	  This driver can also be built as a module.  If so, the module
 	  will be called i2c-mux-mlxcpld.
 
+config I2C_MUX_REGMAP
+	tristate "Register map based I2C multiplexer"
+	depends on REGMAP
+	help
+	  If you say yes to this option, support will be included for a
+	  register map based I2C multiplexer. This driver provides access to
+	  I2C busses connected through a MUX, which is controlled
+	  by a single register through the regmap.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called i2c-mux-regmap.
+
 endmenu
diff --git a/drivers/i2c/muxes/Makefile b/drivers/i2c/muxes/Makefile
index 6d9d865e8518..092dca428a75 100644
--- a/drivers/i2c/muxes/Makefile
+++ b/drivers/i2c/muxes/Makefile
@@ -14,5 +14,6 @@ obj-$(CONFIG_I2C_MUX_PCA9541)	+= i2c-mux-pca9541.o
 obj-$(CONFIG_I2C_MUX_PCA954x)	+= i2c-mux-pca954x.o
 obj-$(CONFIG_I2C_MUX_PINCTRL)	+= i2c-mux-pinctrl.o
 obj-$(CONFIG_I2C_MUX_REG)	+= i2c-mux-reg.o
+obj-$(CONFIG_I2C_MUX_REGMAP)	+= i2c-mux-regmap.o
 
 ccflags-$(CONFIG_I2C_DEBUG_BUS) := -DDEBUG
diff --git a/drivers/i2c/muxes/i2c-mux-regmap.c b/drivers/i2c/muxes/i2c-mux-regmap.c
new file mode 100644
index 000000000000..e155c039a90e
--- /dev/null
+++ b/drivers/i2c/muxes/i2c-mux-regmap.c
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
+/*
+ * Regmap i2c mux driver
+ *
+ * Copyright (C) 2023 Nvidia Technologies Ltd.
+ */
+
+#include <linux/device.h>
+#include <linux/i2c.h>
+#include <linux/i2c-mux.h>
+#include <linux/io.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/platform_data/i2c-mux-regmap.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+
+/* i2c_mux_regmap - mux control structure:
+ * @last_val - last selected register value or -1 if mux deselected;
+ * @pdata: platform data;
+ */
+struct i2c_mux_regmap {
+	int last_val;
+	struct i2c_mux_regmap_platform_data pdata;
+};
+
+static int i2c_mux_regmap_select_chan(struct i2c_mux_core *muxc, u32 chan)
+{
+	struct i2c_mux_regmap *mux = i2c_mux_priv(muxc);
+	int err = 0;
+
+	/* Only select the channel if its different from the last channel */
+	if (mux->last_val != chan) {
+		err = regmap_write(mux->pdata.regmap, mux->pdata.sel_reg_addr, chan);
+		mux->last_val = err < 0 ? -1 : chan;
+	}
+
+	return err;
+}
+
+static int i2c_mux_regmap_deselect(struct i2c_mux_core *muxc, u32 chan)
+{
+	struct i2c_mux_regmap *mux = i2c_mux_priv(muxc);
+
+	/* Deselect active channel */
+	mux->last_val = -1;
+
+	return regmap_write(mux->pdata.regmap, mux->pdata.sel_reg_addr, 0);
+}
+
+/* Probe/reomove functions */
+static int i2c_mux_regmap_probe(struct platform_device *pdev)
+{
+	struct i2c_mux_regmap_platform_data *pdata = dev_get_platdata(&pdev->dev);
+	struct i2c_mux_regmap *mux;
+	struct i2c_adapter *parent;
+	struct i2c_mux_core *muxc;
+	int num, err;
+
+	if (!pdata)
+		return -EINVAL;
+
+	mux = devm_kzalloc(&pdev->dev, sizeof(*mux), GFP_KERNEL);
+	if (!mux)
+		return -ENOMEM;
+
+	memcpy(&mux->pdata, pdata, sizeof(*pdata));
+	parent = i2c_get_adapter(mux->pdata.parent);
+	if (!parent)
+		return -EPROBE_DEFER;
+
+	muxc = i2c_mux_alloc(parent, &pdev->dev, pdata->num_adaps, sizeof(*mux), 0,
+			     i2c_mux_regmap_select_chan, i2c_mux_regmap_deselect);
+	if (!muxc)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, muxc);
+	muxc->priv = mux;
+	mux->last_val = -1; /* force the first selection */
+
+	/* Create an adapter for each channel. */
+	for (num = 0; num < pdata->num_adaps; num++) {
+		err = i2c_mux_add_adapter(muxc, 0, pdata->chan_ids[num], 0);
+		if (err)
+			goto err_i2c_mux_add_adapter;
+	}
+
+	/* Notify caller when all channels' adapters are created. */
+	if (pdata->completion_notify)
+		pdata->completion_notify(pdata->handle, muxc->parent, muxc->adapter);
+
+	return 0;
+
+err_i2c_mux_add_adapter:
+	i2c_mux_del_adapters(muxc);
+	return err;
+}
+
+static int i2c_mux_regmap_remove(struct platform_device *pdev)
+{
+	struct i2c_mux_core *muxc = platform_get_drvdata(pdev);
+
+	i2c_mux_del_adapters(muxc);
+	i2c_put_adapter(muxc->parent);
+
+	return 0;
+}
+
+static struct platform_driver i2c_mux_regmap_driver = {
+	.driver = {
+		.name = "i2c-mux-regmap",
+	},
+	.probe = i2c_mux_regmap_probe,
+	.remove = i2c_mux_regmap_remove,
+};
+
+module_platform_driver(i2c_mux_regmap_driver);
+
+MODULE_AUTHOR("Vadim Pasternak (vadimp@nvidia.com)");
+MODULE_DESCRIPTION("Regmap I2C multiplexer driver");
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_ALIAS("platform:i2c-mux-regmap");
diff --git a/include/linux/platform_data/i2c-mux-regmap.h b/include/linux/platform_data/i2c-mux-regmap.h
new file mode 100644
index 000000000000..a06614e5edd2
--- /dev/null
+++ b/include/linux/platform_data/i2c-mux-regmap.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0 */
+/*
+ * Regmap i2c mux driver
+ *
+ * Copyright (C) 2023 Nvidia Technologies Ltd.
+ */
+
+#ifndef __LINUX_PLATFORM_DATA_I2C_MUX_REGMAP_H
+#define __LINUX_PLATFORM_DATA_I2C_MUX_REGMAP_H
+
+/**
+ * struct i2c_mux_regmap_platform_data - Platform-dependent data for i2c-mux-regmap
+ * @regmap: register map of parent device;
+ * @parent: Parent I2C bus adapter number
+ * @chan_ids - channels array
+ * @num_adaps - number of adapters
+ * @sel_reg_addr - mux select register offset in CPLD space
+ * @reg_size: register size in bytes
+ * @handle: handle to be passed by callback
+ * @completion_notify: callback to notify when all the adapters are created
+ */
+struct i2c_mux_regmap_platform_data {
+	void *regmap;
+	int parent;
+	const unsigned int *chan_ids;
+	int num_adaps;
+	int sel_reg_addr;
+	u8 reg_size;
+	void *handle;
+	int (*completion_notify)(void *handle, struct i2c_adapter *parent,
+				 struct i2c_adapter *adapters[]);
+};
+
+#endif	/* __LINUX_PLATFORM_DATA_I2C_MUX_REGMAP_H */
-- 
2.20.1