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[00/11] LIN Bus support for Linux

Message ID 20240422065114.3185505-1-christoph.fritz@hexdev.de
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Series LIN Bus support for Linux | expand

Message

Christoph Fritz April 22, 2024, 6:51 a.m. UTC
This series is introducing basic Local Interconnect Network (LIN) (ISO
17987) [0] support to the Linux kernel, along with two drivers that make
use of it: An advanced USB adapter and a lightweight serdev driver (for
UARTs equipped with a LIN transceiver).

The LIN bus is common in the automotive industry for connecting
low-level devices like side mirrors, seats, ambient lights, etc.

The LIN bus is a lower-cost bus system with a subset of features of CAN.
Its earlier specification (before ISO) is publicly accessible [1].

This series of patches follows up on a discussion initiated by an RFC
patch series [2].

The core of this series is the first patch, which implements the CAN_LIN
glue driver. It basically utilizes the CAN interface on one side and
for device drivers on the other side it creates a rx() function and
several callbacks.

This approach is non-invasive, as LIN frames (nearly identical to CAN
frames) are just treated as a special case of CAN frames. This approach
eliminates the need for a separate API for LIN, allowing the use of
existing CAN tools, including the CAN broadcast manager.

For the responder part of LIN, when a device responds to a controller
request, it can reply on up to LIN its 64 possible IDs (0...63) with a
maximum of 8 bytes payload.  The response must be sent relatively
quickly, so offloading is used (which is used by most devices anyway).
Devices that do not support offloading (like the lightweight serdev)
handle the list of responses in the driver on a best-effort basis.

The CAN broadcast manager (bcm) makes a good interface for the LIN
userland interface, bcm is therefore enhanced to handle the
configuration of these offload RX frames, so that the device can handle
the response on its own.  As a basic alternative, a sysfs file per LIN
identifier gets also introduced.

The USB device driver for the hexLIN [3] adapter uses the HID protocol
and is located in the drivers/hid directory. Which is a bit uncommon for
a CAN device, but this is a LIN device and mainly a hid driver (and all
hid drivers go into drivers/hid).

The other driver, the UART lin-serdev driver requires support for break
detection, this is addressed by two serdev patches.

The lin-serdev driver has been tested on an ARM SoC, on its uart
(uart-pl011) an adapter board (hexLIN-tty [4]) has been used.  As a
sidenote, in that tty serial driver (amba-pl011.c) it was necessary to
disable DMA_ENGINE to accurately detect breaks [5].

The functions for generating LIN-Breaks and checksums, originally from
a line discipline driver named sllin [6], have been adopted into the
lin-serdev driver.

To make use of the LIN mode configuration (commander or responder)
option, a patch for iproute2 [7] has been made.

The lin-utils [8] provide userland tools for reference, testing, and
evaluation. These utilities are currently separate but may potentially
be integrated into can-utils in the future.

[0]: https://en.wikipedia.org/wiki/Local_Interconnect_Network
[1]: https://www.lin-cia.org/fileadmin/microsites/lin-cia.org/resources/documents/LIN_2.2A.pdf
[2]: https://lwn.net/Articles/916049/
[3]: https://hexdev.de/hexlin
[4]: https://hexdev.de/hexlin#tty
[5]: https://github.com/raspberrypi/linux/issues/5985
[6]: https://github.com/lin-bus/linux-lin/blob/master/sllin/sllin.c
[7]: https://github.com/ch-f/iproute2/tree/lin-feature
[8]: https://github.com/ch-f/lin-utils

Christoph Fritz (11):
  can: Add LIN bus as CAN abstraction
  HID: hexLIN: Add support for USB LIN bus adapter
  tty: serdev: Add flag buffer aware receive_buf_fp()
  tty: serdev: Add method to enable break flags
  dt-bindings: net: can: Add serdev LIN bus dt bindings
  can: Add support for serdev LIN adapters
  can: lin: Add special frame id for rx offload config
  can: bcm: Add LIN answer offloading for responder mode
  can: lin: Handle rx offload config frames
  can: lin: Support setting LIN mode
  HID: hexLIN: Implement ability to update lin mode

 .../bindings/net/can/linux,lin-serdev.yaml    |  29 +
 drivers/hid/Kconfig                           |  19 +
 drivers/hid/Makefile                          |   1 +
 drivers/hid/hid-hexlin.c                      | 594 ++++++++++++++++++
 drivers/hid/hid-ids.h                         |   1 +
 drivers/hid/hid-quirks.c                      |   3 +
 drivers/net/can/Kconfig                       |  26 +
 drivers/net/can/Makefile                      |   2 +
 drivers/net/can/lin-serdev.c                  | 467 ++++++++++++++
 drivers/net/can/lin.c                         | 547 ++++++++++++++++
 drivers/tty/serdev/core.c                     |  11 +
 drivers/tty/serdev/serdev-ttyport.c           |  19 +-
 include/linux/serdev.h                        |  19 +-
 include/net/lin.h                             | 105 ++++
 include/uapi/linux/can/bcm.h                  |   5 +-
 include/uapi/linux/can/netlink.h              |   2 +
 net/can/bcm.c                                 |  74 ++-
 17 files changed, 1918 insertions(+), 6 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/net/can/linux,lin-serdev.yaml
 create mode 100644 drivers/hid/hid-hexlin.c
 create mode 100644 drivers/net/can/lin-serdev.c
 create mode 100644 drivers/net/can/lin.c
 create mode 100644 include/net/lin.h

Comments

Krzysztof Kozlowski April 22, 2024, 7:54 a.m. UTC | #1
On 22/04/2024 08:51, Christoph Fritz wrote:
> Add documentation of device tree bindings for serdev UART LIN-Bus
> devices equipped with LIN transceivers.

A nit, subject: drop second/last, redundant "dt bindings". The
"dt-bindings" prefix is already stating that these are bindings.
See also:
https://elixir.bootlin.com/linux/v6.7-rc8/source/Documentation/devicetree/bindings/submitting-patches.rst#L18

> 
> Signed-off-by: Christoph Fritz <christoph.fritz@hexdev.de>
> ---
>  .../bindings/net/can/linux,lin-serdev.yaml    | 29 +++++++++++++++++++
>  1 file changed, 29 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/net/can/linux,lin-serdev.yaml
> 
> diff --git a/Documentation/devicetree/bindings/net/can/linux,lin-serdev.yaml b/Documentation/devicetree/bindings/net/can/linux,lin-serdev.yaml
> new file mode 100644
> index 0000000000000..cb4e932ff249c
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/net/can/linux,lin-serdev.yaml
> @@ -0,0 +1,29 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/net/can/linux,lin-serdev.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Linux serdev LIN-Bus Support

This looks like Linux binding, but we expect here description of hardware.


> +
> +description: |
> +  LIN-Bus support for UART devices equipped with LIN transceivers,
> +  utilizing the Serial Device Bus (serdev) interface.

serdev is Linux thingy, AFAIR. Please describe the hardware.

> +
> +  For more details on an adapter, visit: https://hexdev.de/hexlin#tty
> +
> +properties:
> +  compatible:
> +    const: linux,lin-serdev

Feels confusing. Your link describes real hardware, but you wrote
bindings for software construct.

If you add this to DT, then it is hard-wired on the board, right? If so,
how this could be a software construct?


> +
> +required:
> +  - compatible
> +
> +examples:
> +  - |
> +    &uart2 {

& does not make much sense here. I think you wanted it to be serial bus,
so serial.

> +      status = "okay";

Drop, it was not disabled anywhere.


> +      linbus {
> +        compatible = "linux,lin-serdev";
> +      };
> +    };

Best regards,
Krzysztof
Rob Herring April 22, 2024, 8:26 a.m. UTC | #2
On Mon, 22 Apr 2024 08:51:08 +0200, Christoph Fritz wrote:
> Add documentation of device tree bindings for serdev UART LIN-Bus
> devices equipped with LIN transceivers.
> 
> Signed-off-by: Christoph Fritz <christoph.fritz@hexdev.de>
> ---
>  .../bindings/net/can/linux,lin-serdev.yaml    | 29 +++++++++++++++++++
>  1 file changed, 29 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/net/can/linux,lin-serdev.yaml
> 

My bot found errors running 'make dt_binding_check' on your patch:

yamllint warnings/errors:

dtschema/dtc warnings/errors:
/builds/robherring/dt-review-ci/linux/Documentation/devicetree/bindings/net/can/linux,lin-serdev.yaml: 'maintainers' is a required property
	hint: Metaschema for devicetree binding documentation
	from schema $id: http://devicetree.org/meta-schemas/base.yaml#
/builds/robherring/dt-review-ci/linux/Documentation/devicetree/bindings/net/can/linux,lin-serdev.yaml: 'oneOf' conditional failed, one must be fixed:
	'unevaluatedProperties' is a required property
	'additionalProperties' is a required property
	hint: Either unevaluatedProperties or additionalProperties must be present
	from schema $id: http://devicetree.org/meta-schemas/core.yaml#
Error: Documentation/devicetree/bindings/net/can/linux,lin-serdev.example.dts:18.9-15 syntax error
FATAL ERROR: Unable to parse input tree
make[2]: *** [scripts/Makefile.lib:427: Documentation/devicetree/bindings/net/can/linux,lin-serdev.example.dtb] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [/builds/robherring/dt-review-ci/linux/Makefile:1430: dt_binding_check] Error 2
make: *** [Makefile:240: __sub-make] Error 2

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/project/devicetree-bindings/patch/20240422065114.3185505-6-christoph.fritz@hexdev.de

The base for the series is generally the latest rc1. A different dependency
should be noted in *this* patch.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit after running the above command yourself. Note
that DT_SCHEMA_FILES can be set to your schema file to speed up checking
your schema. However, it must be unset to test all examples with your schema.
Krzysztof Kozlowski April 23, 2024, 6:55 a.m. UTC | #3
On 22/04/2024 08:51, Christoph Fritz wrote:
> Add documentation of device tree bindings for serdev UART LIN-Bus
> devices equipped with LIN transceivers.
> 
> Signed-off-by: Christoph Fritz <christoph.fritz@hexdev.de>
> ---

Please test patches before sending...

Best regards,
Krzysztof
Jiri Slaby April 24, 2024, 6:15 a.m. UTC | #4
On 23. 04. 24, 11:33, Christoph Fritz wrote:
>>> --- /dev/null
>>> +++ b/include/net/lin.h
>>> @@ -0,0 +1,97 @@
...
>>> +/* special ID descriptions for LIN */
>>> +#define LIN_ENHANCED_CKSUM_FLAG	0x00000100U
>>> +
>>> +static const unsigned char lin_id_parity_tbl[] = {
>>
>> This ends up in every translation unit you include lin.h into. Bad.
> 
> This is also being used by a serial lin driver. But I guess most of the drivers have no need for this. Mhm, ... any ideas?

If needs be, put it to a .c and keep an extern here.

thanks,