[RFC,v5,0/5] can: bxcan: add support for ST bxCAN controller

The series adds support for the basic extended CAN controller (bxCAN)
found in many low- to middle-end STM32 SoCs.

The driver design (one core module and one driver module) was inspired
by other ST drivers (e. g. drivers/iio/adc/stm32-adc.c,
drivers/iio/adc/stm32-adc-core.c) where device instances share resources.
The shared resources functions are implemented in the core module, the
device driver in a separate module.

The driver has been tested on the stm32f469i-discovery board with a
kernel version 5.19.0-rc2 in loopback + silent mode:

ip link set can0 type can bitrate 125000 loopback on listen-only on
ip link set up can0
candump can0 -L &
cansend can0 300#AC.AB.AD.AE.75.49.AD.D1

For uboot and kernel compilation, as well as for rootfs creation I used
buildroot:

make stm32f469_disco_sd_defconfig
make

but I had to patch can-utils and busybox as can-utils and iproute are
not compiled for MMU-less microcotrollers. In the case of can-utils,
replacing the calls to fork() with vfork(), I was able to compile the
package with working candump and cansend applications, while in the
case of iproute, I ran into more than one problem and finally I decided
to extend busybox's ip link command for CAN-type devices. I'm still
wondering if it was really necessary, but this way I was able to test
the driver.

Changes in v5:
- Add Rob Herring's Acked-by tag.
- Add Rob Herring's Reviewed-by tag.
- Put static in front of bxcan_enable_filters() definition.

Changes in v4:
- Remove "st,stm32f4-bxcan-core" compatible. In this way the can nodes
 (compatible "st,stm32f4-bxcan") are no longer children of a parent
  node with compatible "st,stm32f4-bxcan-core".
- Add the "st,gcan" property (global can memory) to can nodes which
  references a "syscon" node containing the shared clock and memory
  addresses.
- Replace the node can@40006400 (compatible "st,stm32f4-bxcan-core")
  with the gcan@40006600 node ("sysnode" compatible). The gcan node
  contains clocks and memory addresses shared by the two can nodes
  of which it's no longer the parent.
- Add to can nodes the "st,gcan" property (global can memory) which
  references the gcan@40006600 node ("sysnode compatibble).
- Add "dt-bindings: arm: stm32: add compatible for syscon gcan node" patch.
- Drop the core driver. Thus bxcan-drv.c has been renamed to bxcan.c and
  moved to the drivers/net/can folder. The drivers/net/can/bxcan directory
  has therefore been removed.
- Use the regmap_*() functions to access the shared memory registers.
- Use spinlock to protect bxcan_rmw().
- Use 1 space, instead of tabs, in the macros definition.
- Drop clock ref-counting.
- Drop unused code.
- Drop the _SHIFT macros and use FIELD_GET()/FIELD_PREP() directly.
- Add BXCAN_ prefix to lec error codes.
- Add the macro BXCAN_RX_MB_NUM.
- Enable time triggered mode and use can_rx_offload().
- Use readx_poll_timeout() in function with timeouts.
- Loop from tail to head in bxcan_tx_isr().
- Check bits of tsr register instead of pkts variable in bxcan_tx_isr().
- Don't return from bxcan_handle_state_change() if skb/cf are NULL.
- Enable/disable the generation of the bus error interrupt depending
  on can.ctrlmode & CAN_CTRLMODE_BERR_REPORTING.
- Don't return from bxcan_handle_bus_err() if skb is NULL.
- Drop statistics updating from bxcan_handle_bus_err().
- Add an empty line in front of 'return IRQ_HANDLED;'
- Rename bxcan_start() to bxcan_chip_start().
- Rename bxcan_stop() to bxcan_chip_stop().
- Disable all IRQs in bxcan_chip_stop().
- Rename bxcan_close() to bxcan_ndo_stop().
- Use writel instead of bxcan_rmw() to update the dlc register.

Changes in v3:
- Remove 'Dario Binacchi <dariobin@libero.it>' SOB.
- Add description to the parent of the two child nodes.
- Move "patterProperties:" after "properties: in top level before "required".
- Add "clocks" to the "required:" list of the child nodes.
- Remove 'Dario Binacchi <dariobin@libero.it>' SOB.
- Add "clocks" to can@0 node.
- Remove 'Dario Binacchi <dariobin@libero.it>' SOB.
- Remove a blank line.
- Remove 'Dario Binacchi <dariobin@libero.it>' SOB.
- Fix the documentation file path in the MAINTAINERS entry.
- Do not increment the "stats->rx_bytes" if the frame is remote.
- Remove pr_debug() call from bxcan_rmw().

Changes in v2:
- Change the file name into 'st,stm32-bxcan-core.yaml'.
- Rename compatibles:
  - st,stm32-bxcan-core -> st,stm32f4-bxcan-core
  - st,stm32-bxcan -> st,stm32f4-bxcan
- Rename master property to st,can-master.
- Remove the status property from the example.
- Put the node child properties as required.
- Remove a blank line.
- Fix sparse errors.
- Create a MAINTAINERS entry.
- Remove the print of the registers address.
- Remove the volatile keyword from bxcan_rmw().
- Use tx ring algorithm to manage tx mailboxes.
- Use can_{get|put}_echo_skb().
- Update DT properties.

Dario Binacchi (5):
  dt-bindings: arm: stm32: add compatible for syscon gcan node
  dt-bindings: net: can: add STM32 bxcan DT bindings
  ARM: dts: stm32: add CAN support on stm32f429
  ARM: dts: stm32: add pin map for CAN controller on stm32f4
  can: bxcan: add support for ST bxCAN controller

 .../bindings/arm/stm32/st,stm32-syscon.yaml   |    2 +
 .../bindings/net/can/st,stm32-bxcan.yaml      |   83 ++
 MAINTAINERS                                   |    7 +
 arch/arm/boot/dts/stm32f4-pinctrl.dtsi        |   30 +
 arch/arm/boot/dts/stm32f429.dtsi              |   29 +
 drivers/net/can/Kconfig                       |   12 +
 drivers/net/can/Makefile                      |    1 +
 drivers/net/can/bxcan.c                       | 1110 +++++++++++++++++
 8 files changed, 1274 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/net/can/st,stm32-bxcan.yaml
 create mode 100644 drivers/net/can/bxcan.c