Re: [PATCH RFC 0/3] reset: syscon-reboot: add "reg" property support

[Rob Herring <robh+dt@kernel.org>]

On Tue, Nov 2, 2021 at 10:22 AM Rafał Miłecki <zajec5@gmail.com> wrote:
>
> From: Rafał Miłecki <rafal@milecki.pl>
>
> During my work on MFD binding for Broadcom's TWD block I received
> comment from Rob saying that "syscon-reboot" should use "reg" property.
> I'm not sure if my understanding & implementation are correct so I'm
> sending this RFC.
>
> What bothers me is non-standard "reg" property usage. Treating it as a
> simple (unsigned) integer number means different logic when it comes to
> ranges.

It shouldn't be. The idea is that 'reg' works like normal. See below.

> Consider this example:
>
> timer@400 {
>         compatible = "simple-mfd", "syscon";
>         reg = <0x400 0x3c>;
>         ranges;

ranges = <0 0x400 0x100>; // Just guessing for size

>
>         #address-cells = <1>;
>         #size-cells = <1>;
>
>         reboot@434 {

reboot@34

Just reading 'reg' is fine, but really, Linux should be either getting
the translated address or have a function to get the offset from the
parent base. IOW, it should also work if you just changed 'reg' to
'<0x434 0x4>'.

>                 compatible = "syscon-reboot";
>                 reg = <0x34 0x4>;
>                 mask = <0x1>;
>         };
> };
>
> I've reboot@434 node with reg 0x34. Also 0x4 is ignored but must be
> present because of of MFD addressing.
>
> Please review this idea / binding / implementation.
>
> Rafał Miłecki (3):
>   dt-bindings: power: reset: syscon-reboot: use non-deprecated example
>   dt-bindings: power: reset: syscon-reboot: add "reg" property
>   power: reset: syscon-reboot: support "reg" property
>
>  .../bindings/power/reset/syscon-reboot.yaml   | 28 +++++++++++++------
>  drivers/power/reset/syscon-reboot.c           |  9 ++++--
>  2 files changed, 26 insertions(+), 11 deletions(-)
>
> --
> 2.31.1
>