can: Kconfig: add CONFIG_CAN_RX_OFFLOAD

Only a few drivers rely on the CAN rx offload framework (as of the
writing of this patch, only four: flexcan, m_can, mcp251xfd and
ti_hecc). Split it out of can-dev and add a new config symbol:
CAN_RX_OFFLOAD.

The drivers relying on CAN rx offload are in different sub
folders. Make CAN_RX_OFFLOAD an hidden option and tag all the drivers
depending on that feature with "select CAN_RX_OFFLOAD" so that the
option gets automatically enabled if and only if one of those drivers
is chosen.

Link: https://lore.kernel.org/all/20220610143009.323579-5-mailhol.vincent@wanadoo.frSuggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Acked-by: Max Staudt <max@enpas.org>
Tested-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/Kconfig

@@ -102,6 +102,9 @@ config CAN_CALC_BITTIMING
 
 	  If unsure, say Y.
 
+config CAN_RX_OFFLOAD
+	bool
+
 config CAN_AT91
 	tristate "Atmel AT91 onchip CAN controller"
 	depends on (ARCH_AT91 || COMPILE_TEST) && HAS_IOMEM
@@ -113,6 +116,7 @@ config CAN_FLEXCAN
 	tristate "Support for Freescale FLEXCAN based chips"
 	depends on OF || COLDFIRE || COMPILE_TEST
 	depends on HAS_IOMEM
+	select CAN_RX_OFFLOAD
 	help
 	  Say Y here if you want to support for Freescale FlexCAN.
 
@@ -162,6 +166,7 @@ config CAN_SUN4I
 config CAN_TI_HECC
 	depends on ARM
 	tristate "TI High End CAN Controller"
+	select CAN_RX_OFFLOAD
 	help
 	  Driver for TI HECC (High End CAN Controller) module found on many
 	  TI devices. The device specifications are available from www.ti.com

drivers/net/can/dev/Makefile

@@ -9,4 +9,4 @@ can-dev-$(CONFIG_CAN_NETLINK) += bittiming.o
 can-dev-$(CONFIG_CAN_NETLINK) += dev.o
 can-dev-$(CONFIG_CAN_NETLINK) += length.o
 can-dev-$(CONFIG_CAN_NETLINK) += netlink.o
-can-dev-$(CONFIG_CAN_NETLINK) += rx-offload.o
+can-dev-$(CONFIG_CAN_RX_OFFLOAD) += rx-offload.o

drivers/net/can/m_can/Kconfig

 # SPDX-License-Identifier: GPL-2.0-only
 menuconfig CAN_M_CAN
 	tristate "Bosch M_CAN support"
+	select CAN_RX_OFFLOAD
 	help
 	  Say Y here if you want support for Bosch M_CAN controller framework.
 	  This is common support for devices that embed the Bosch M_CAN IP.

drivers/net/can/spi/mcp251xfd/Kconfig

@@ -2,6 +2,7 @@
 
 config CAN_MCP251XFD
 	tristate "Microchip MCP251xFD SPI CAN controllers"
+	select CAN_RX_OFFLOAD
 	select REGMAP
 	select WANT_DEV_COREDUMP
 	help