Re: [PATCH v4 1/7] dt-bindings: soc: Describe the BCM6846 Power Management Bus

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Medium] dt-bindings: soc: bcm6846-pmb: child nodes split single PMB
  by Linux subsystem
--

commit 6235ca071e36f4e363a6b36688dc2c4a38089eb7
Author: Linus Walleij <linusw@kernel.org>

dt-bindings: soc: Describe the BCM6846 Power Management Bus

This commit adds Devicetree binding schemas and header constants for the
Broadcom BCM6846 Power Management Bus (PMB) and its clock, power, reset,
and PVTMON child controllers.

> diff --git a/Documentation/devicetree/bindings/soc/bcm/brcm,bcm6846-pmb.yaml b/Documentation/devicetree/bindings/soc/bcm/brcm,bcm6846-pmb.yaml
> new file mode 100644
> index 0000000000000..9782a27ff0759
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/soc/bcm/brcm,bcm6846-pmb.yaml

[ ... ]

> +  Child nodes describe independent hardware blocks accessed over the PMB.
> +  These provide global resources and even resources for each other.
> +
> +properties:
> +  compatible:
> +    const: brcm,bcm6846-pmb
> +
> +  reg:
> +    maxItems: 1
> +    description: PMB configuration, keyhole and address mapping registers
> +
> +  power-controller:
> +    type: object
> +    $ref: /schemas/power/brcm,bcm6846-pmb-power.yaml#
> +
> +  clock-controller:
> +    type: object
> +    $ref: /schemas/clock/brcm,bcm6846-pmb-clock.yaml#
> +
> +  reset-controller:
> +    type: object
> +    $ref: /schemas/reset/brcm,bcm6846-pmb-reset.yaml#
> +
> +  hwmon:
> +    type: object
> +    $ref: /schemas/hwmon/brcm,bcm6846-pmb-pvtmon.yaml#

[Severity: Medium]
As reported by Philipp Zabel on RFC [1], should #clock-cells,
#power-domain-cells, #reset-cells, #thermal-sensor-cells, and the
reference clock be placed directly on the brcm,bcm6846-pmb node instead
of requiring four address-less child nodes?

The child nodes have no hardware address space of their own and partition
the PMB keyhole interface by Linux subsystem rather than independent
hardware blocks, encoding the Linux MFD driver split into the Devicetree
ABI.  In the driver patches in this series, power-controller,
clock-controller, and reset-controller all access the same BPCM slave
devices through the parent regmap, with power-controller and
clock-controller modifying different bitfields of the same 32-bit BPCM
zone control words (offset 32 + zone * 8).  Similarly, the clocks and
resets properties on the hwmon child node (BCM6846_CLK_PVTMON and
BCM6846_RESET_PVTMON) toggle bits 12:8, 2, and 0 of PVTMON's own
PVTMON_CONFIG register (bus 1, device 6, word 17).

The Linux driver for brcm,bcm6846-pmb can still instantiate child
platform or auxiliary devices internally while exposing the provider cells
on the parent PMB node.

[1] https://lore.kernel.org/r/f1c24a603964302ec1462b1cea790a2a7079fb3d.camel@pengutronix.de

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111-xg6846b-bcmbca-xrdp-reset-v4-0-17035a5e8ad2@kernel.org?part=1