net: wan: Add framer framework support

A framer is a component in charge of an E1/T1 line interface.
Connected usually to a TDM bus, it converts TDM frames to/from E1/T1
frames. It also provides information related to the E1/T1 line.

The framer framework provides a set of APIs for the framer drivers
(framer provider) to create/destroy a framer and APIs for the framer
users (framer consumer) to obtain a reference to the framer, and
use the framer.

This basic implementation provides a framer abstraction for:
 - power on/off the framer
 - get the framer status (line state)
 - be notified on framer status changes
 - get/set the framer configuration

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20231128132534.258459-2-herve.codina@bootlin.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/net/wan/Kconfig

@@ -95,6 +95,8 @@ config HDLC_X25
 comment "X.25/LAPB support is disabled"
 	depends on HDLC && (LAPB!=m || HDLC!=m) && LAPB!=y
 
+source "drivers/net/wan/framer/Kconfig"
+
 config PCI200SYN
 	tristate "Goramo PCI200SYN support"
 	depends on HDLC && PCI

drivers/net/wan/Makefile

@@ -14,6 +14,8 @@ obj-$(CONFIG_HDLC_FR)		+= hdlc_fr.o
 obj-$(CONFIG_HDLC_PPP)		+= hdlc_ppp.o
 obj-$(CONFIG_HDLC_X25)		+= hdlc_x25.o
 
+obj-y				+= framer/
+
 obj-$(CONFIG_FARSYNC)		+= farsync.o
 
 obj-$(CONFIG_LAPBETHER)		+= lapbether.o

drivers/net/wan/framer/Kconfig

@@ -0,0 +1,25 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# FRAMER
+#
+
+menuconfig FRAMER
+	tristate "Framer Subsystem"
+	help
+	  A framer is a component in charge of an E1/T1 line interface.
+	  Connected usually to a TDM bus, it converts TDM frames to/from E1/T1
+	  frames. It also provides information related to the E1/T1 line.
+	  Used with HDLC, the network can be reached through the E1/T1 line.
+
+	  This framework is designed to provide a generic interface for framer
+	  devices present in the kernel. This layer will have the generic
+	  API by which framer drivers can create framer using the framer
+	  framework and framer users can obtain reference to the framer.
+	  All the users of this framework should select this config.
+
+if FRAMER
+
+config GENERIC_FRAMER
+	bool
+
+endif # FRAMER

drivers/net/wan/framer/Makefile

@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for the framer drivers.
+#
+
+obj-$(CONFIG_GENERIC_FRAMER)			+= framer-core.o