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Subject[RFC] spi: add spi multiplexing functions for dt
Date
Like I2C busses SPI devices can also sit behind multiplexers.
This patch adds is based off the I2C implementation and allows
description in the devicetree.

Signed-off-by: Ben Whitten <ben.whitten@gmail.com>
---
drivers/spi/Kconfig | 10 +++
drivers/spi/Makefile | 3 +
drivers/spi/spi-mux.c | 181 ++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/spi-mux.h | 55 +++++++++++++++
4 files changed, 249 insertions(+)
create mode 100644 drivers/spi/spi-mux.c
create mode 100644 include/linux/spi-mux.h

diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index a75f2a2..58eba70 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -51,6 +51,16 @@ config SPI_MASTER

if SPI_MASTER

+config SPI_MUX
+ tristate "SPI bus multiplexing support"
+ help
+ Say Y here if you want the SPI core to support the ability to
+ handle multiplexed SPI bus topologies, by presenting each
+ multiplexed segment as an SPI controller.
+
+ This support is also available as a module. If so, the module
+ will be called spi-mux.
+
comment "SPI Master Controller Drivers"

config SPI_ALTERA
diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
index 8e0cda7..ef525fe 100644
--- a/drivers/spi/Makefile
+++ b/drivers/spi/Makefile
@@ -109,6 +109,9 @@ obj-$(CONFIG_SPI_XLP) += spi-xlp.o
obj-$(CONFIG_SPI_XTENSA_XTFPGA) += spi-xtensa-xtfpga.o
obj-$(CONFIG_SPI_ZYNQMP_GQSPI) += spi-zynqmp-gqspi.o

+# SPI muxs
+obj-$(CONFIG_SPI_MUX) += spi-mux.o
+
# SPI slave protocol handlers
obj-$(CONFIG_SPI_SLAVE_TIME) += spi-slave-time.o
obj-$(CONFIG_SPI_SLAVE_SYSTEM_CONTROL) += spi-slave-system-control.o
diff --git a/drivers/spi/spi-mux.c b/drivers/spi/spi-mux.c
new file mode 100644
index 0000000..a2008c1
--- /dev/null
+++ b/drivers/spi/spi-mux.c
@@ -0,0 +1,181 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for an SPI multiplexer
+ *
+ * Copyright (c) 2018 Ben Whitten
+ */
+
+#include <linux/spi/spi.h>
+#include <linux/spi-mux.h>
+#include <linux/of.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+struct spi_mux_priv {
+ struct spi_controller *controller;
+ struct spi_mux_core *muxc;
+ u32 chan_id;
+};
+
+struct spi_mux_core *spi_mux_alloc(struct spi_controller *parent,
+ struct device *dev,
+ int max_controllers,
+ int sizeof_priv,
+ int (*select)(struct spi_mux_core *, u32),
+ int (*deselect)(struct spi_mux_core *, u32),
+ int (*transfer_one_message)
+ (struct spi_controller *controller,
+ struct spi_message *msg))
+{
+ struct spi_mux_core *muxc;
+
+ muxc = devm_kzalloc(dev, sizeof(*muxc)
+ + max_controllers * sizeof(muxc->controller[0])
+ + sizeof_priv, GFP_KERNEL);
+ if (!muxc)
+ return NULL;
+ if (sizeof_priv)
+ muxc->priv = &muxc->controller[max_controllers];
+
+ muxc->parent = parent;
+ muxc->dev = dev;
+
+ muxc->select = select;
+ muxc->deselect = deselect;
+ muxc->transfer_one_message = transfer_one_message;
+ muxc->max_controllers = max_controllers;
+
+ return muxc;
+}
+EXPORT_SYMBOL_GPL(spi_mux_alloc);
+
+u32 spi_mux_get_chan_id(struct spi_controller *controller)
+{
+ struct spi_mux_priv *priv = spi_controller_get_devdata(controller);
+
+ return priv->chan_id;
+}
+EXPORT_SYMBOL_GPL(spi_mux_get_chan_id);
+
+static int spi_mux_transfer_one_message(struct spi_controller *controller,
+ struct spi_message *msg)
+{
+ struct spi_mux_priv *priv = spi_controller_get_devdata(controller);
+ struct spi_mux_core *muxc = priv->muxc;
+ struct spi_device *spi = to_spi_device(muxc->dev);
+ int ret;
+
+ ret = muxc->select(muxc, priv->chan_id);
+ if (ret < 0)
+ return ret;
+
+ /* If we have a custom transfer, use it */
+ if (muxc->transfer_one_message)
+ ret = muxc->transfer_one_message(controller, msg);
+ else
+ ret = spi_sync(spi, msg);
+
+ if (muxc->deselect)
+ muxc->deselect(muxc, priv->chan_id);
+
+ return ret;
+}
+
+static int spi_mux_add_controller(struct spi_mux_core *muxc, u32 chan_id)
+{
+ struct spi_controller *controller;
+ struct spi_mux_priv *priv;
+ int ret;
+
+ if (muxc->num_controllers >= muxc->max_controllers) {
+ dev_err(muxc->dev, "No room for more spi-mux controllers");
+ return -EINVAL;
+ }
+
+ controller = spi_alloc_master(muxc->dev, sizeof(*priv));
+ if (!controller)
+ return -ENOMEM;
+ priv = spi_controller_get_devdata(controller);
+
+ /* Setup private controller data */
+ priv->muxc = muxc;
+ priv->controller = controller;
+ priv->chan_id = chan_id;
+
+ priv->controller->transfer_one_message = spi_mux_transfer_one_message;
+
+ /* Look for the child of this controller */
+ if (muxc->dev->of_node) {
+ struct device_node *dev_node = muxc->dev->of_node;
+ struct device_node *mux_node, *child = NULL;
+ u32 reg;
+
+ mux_node = of_get_child_by_name(dev_node, "spi-mux");
+ if (!mux_node)
+ mux_node = of_node_get(dev_node);
+
+ for_each_child_of_node(mux_node, child) {
+ ret = of_property_read_u32(child, "reg", &reg);
+ if (ret)
+ continue;
+ if (chan_id == reg)
+ break;
+ }
+
+ priv->controller->dev.of_node = child;
+ of_node_put(mux_node);
+ }
+
+ ret = devm_spi_register_controller(muxc->dev, priv->controller);
+ if (ret) {
+ spi_controller_put(priv->controller);
+ dev_err(muxc->dev, "Problem registering spi controller: %d\n",
+ ret);
+ return ret;
+ }
+
+ muxc->controller[muxc->num_controllers++] = priv->controller;
+
+ return ret;
+}
+
+static void spi_mux_del_controllers(struct spi_mux_core *muxc)
+{
+ struct spi_controller *controller =
+ muxc->controller[--muxc->num_controllers];
+ struct device_node *np = controller->dev.of_node;
+
+ muxc->controller[muxc->num_controllers] = NULL;
+ of_node_put(np);
+}
+
+static void devm_spi_mux_del_controllers(struct device *dev, void *res)
+{
+ spi_mux_del_controllers(*(struct spi_mux_core **)res);
+}
+
+int devm_spi_mux_add_controller(struct spi_mux_core *muxc, u32 chan_id)
+{
+ struct spi_mux_core **ptr;
+ int ret;
+
+ ptr = devres_alloc(devm_spi_mux_del_controllers, sizeof(*ptr),
+ GFP_KERNEL);
+ if (!ptr)
+ return -ENOMEM;
+
+ ret = spi_mux_add_controller(muxc, chan_id);
+ if (!ret) {
+ *ptr = muxc;
+ devres_add(muxc->dev, ptr);
+ } else {
+ devres_free(ptr);
+ }
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(devm_spi_mux_add_controller);
+
+MODULE_AUTHOR("Ben Whitten <ben.whitten@gmail.com>");
+MODULE_DESCRIPTION("SPI driver for multiplexed SPI busses");
+MODULE_LICENSE("GPL v2");
diff --git a/include/linux/spi-mux.h b/include/linux/spi-mux.h
new file mode 100644
index 0000000..5978f86
--- /dev/null
+++ b/include/linux/spi-mux.h
@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for an SPI multiplexer
+ *
+ * Copyright (c) 2018 Ben Whitten
+ */
+
+#ifndef _LINUX_SPI_MUX_H_
+#define _LINUX_SPI_MUX_H_
+
+#ifdef __KERNEL__
+
+struct spi_mux_core {
+ struct spi_controller *parent;
+ struct device *dev;
+
+ void *priv;
+
+ int (*select)(struct spi_mux_core *, u32 chan_id);
+ int (*deselect)(struct spi_mux_core *, u32 chan_id);
+ int (*transfer_one_message)(struct spi_controller *controller,
+ struct spi_message *msg);
+
+ int num_controllers;
+ int max_controllers;
+ struct spi_controller *controller[0];
+};
+
+struct spi_mux_core *spi_mux_alloc(struct spi_controller *parent,
+ struct device *dev,
+ int max_controllers,
+ int sizeof_priv,
+ int (*select)(struct spi_mux_core *, u32),
+ int (*deselect)(struct spi_mux_core *, u32),
+ int (*transfer_one_message)
+ (struct spi_controller *controller,
+ struct spi_message *msg));
+
+static inline void *spi_mux_priv(struct spi_mux_core *muxc)
+{
+ return muxc->priv;
+}
+
+u32 spi_mux_get_chan_id(struct spi_controller *controller);
+
+/*
+ * Called to create an spi bus on a multiplexed bus segment.
+ * The chan_id parameter is passed to the select and deselect
+ * callback functions to perform hardware-specific mux control.
+ */
+int devm_spi_mux_add_controller(struct spi_mux_core *muxc, u32 chan_id);
+
+#endif /* __KERNEL__ */
+
+#endif /* _LINUX_SPI_MUX_H_ */
--
2.7.4
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