[PATCH v2 1/2] mux: core: add a brief overview of the subsystem

[Peter Rosin <peda@axentia.se>]

Preparation for adding the mux subsystem to the driver-api documenation.

Signed-off-by: Peter Rosin <peda@axentia.se>
---
 drivers/mux/core.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/mux/core.c b/drivers/mux/core.c
index d1271c1ee23c..ccb5479f8a39 100644
--- a/drivers/mux/core.c
+++ b/drivers/mux/core.c
@@ -7,6 +7,43 @@
  * Author: Peter Rosin <peda@axentia.se>
  */
 
+/**
+ * DOC: overview
+ *
+ * The multiplexer subsystem uses the following naming:
+ *
+ * - Multiplexer controller: the piece of hardware that changes the
+ *   state of a hardware multiplexer (or indeed, several parallel
+ *   multiplexers).
+ *
+ * - Multiplexer chip: a collection of multiplexer controllers, in a chip.
+ *
+ * - Multiplexer driver: the device driver that interacts with and handles the
+ *   above hardware. The driver has structures representing a mux chip and mux
+ *   controllers.
+ *
+ * - Multiplexer consumer: the driver that needs to manipulate the hardware
+ *   multiplexer.
+ *
+ * The mux subsystem provides a framework for multiplexer drivers that can
+ * be used by other consumer drivers. It has two primary purposes.
+ *
+ * First, when a consumer driver can be used with one of several multiplexers,
+ * depending on hardware configuration, the actual multiplexer is abstracted
+ * away in the mux drivers. The multiplexer consumer driver can be neater
+ * this way.
+ *
+ * Second, when two consumers -- possibly from different subsystems -- compete
+ * for the same mux controller, i.e. when one mux controller muxes more than
+ * one signal, the mux framework provides locking.
+ *
+ * If the mux driver is so special that it will only ever have a single
+ * consumer, and that consumer can really only work with that one mux driver,
+ * the mux framework is not really providing much benefit. It might be a better
+ * idea to simply manipulate the mux hardware directly from the consumer
+ * driver.
+ */
+
 #define pr_fmt(fmt) "mux-core: " fmt
 
 #include <linux/device.h>
-- 
2.11.0