linux-kernel - Re: [PATCH 3/8] dt-bindings: mfd: Add Google GS101 TMU Syscon

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Message-ID: <200d34bf-150e-4f8a-b400-2f54863502ac@linaro.org>
Date: Thu, 15 Jan 2026 16:53:36 +0200
From: Tudor Ambarus <tudor.ambarus@...aro.org>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, Zhang Rui <rui.zhang@...el.com>,
 Lukasz Luba <lukasz.luba@....com>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Lee Jones <lee@...nel.org>,
 Alim Akhtar <alim.akhtar@...sung.com>,
 Peter Griffin <peter.griffin@...aro.org>,
 André Draszik <andre.draszik@...aro.org>,
 Bartlomiej Zolnierkiewicz <bzolnier@...il.com>, Kees Cook <kees@...nel.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>, willmcvicker@...gle.com,
 jyescas@...gle.com, shin.son@...sung.com, linux-pm@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-samsung-soc@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH 3/8] dt-bindings: mfd: Add Google GS101 TMU Syscon

On 1/15/26 3:36 PM, Krzysztof Kozlowski wrote:
> On Wed, Jan 14, 2026 at 02:16:31PM +0000, Tudor Ambarus wrote:
>> Document the bindings for the Thermal Management Unit (TMU) System
>> Controller found on Google GS101 SoCs.
>>
>> This memory-mapped block exposes the registers required for reading
>> thermal interrupt status bits. It functions as a syscon provider,
> 
> I don't think this is syscon, but the actual TMU. Syscon is various,
> unrelated system configuration registers.
> 
>> allowing the main thermal driver to access these registers while
>> the firmware manages the core thermal logic.
>>
>> Signed-off-by: Tudor Ambarus <tudor.ambarus@...aro.org>
>> ---
>>  .../bindings/mfd/google,gs101-tmu-syscon.yaml      | 37 ++++++++++++++++++++++
>>  1 file changed, 37 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/mfd/google,gs101-tmu-syscon.yaml b/Documentation/devicetree/bindings/mfd/google,gs101-tmu-syscon.yaml
>> new file mode 100644
>> index 0000000000000000000000000000000000000000..6a11e43abeaa23ee473be2153478436856277714
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/mfd/google,gs101-tmu-syscon.yaml
> 
> Not MFD either, but soc.

You are right, it's not a syscon, it's just a normal thermal IP block
from which I need to access the interrupt pending registers.

Then I guess I shall describe the new binding in bindings/thermal/,
please correct me if I'm wrong.

> 
>> @@ -0,0 +1,37 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/mfd/google,gs101-tmu-syscon.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Google GS101 TMU System Controller
>> +
>> +maintainers:
>> +  - Tudor Ambarus <tudor.ambarus@...aro.org>
>> +
>> +description: |
> 
> Drop |
> 
>> +  The TMU System Controller provides a memory-mapped interface for
>> +  accessing the interrupt status registers of the Thermal Management
>> +  Unit. It is used as a syscon provider for the main TMU driver.
> 
> No, it is not a syscon provider. Entire last sentence is incorrect. You
> must describe here hardware and this hardware does not provide any sort
> of syscon to any sort of driver.
> 

Indeed.

I'm going to link the ACPM TMU child node with the TMU node via a
"samsung,tmu-regs" property.

Some concern that I have is that I describe the clocks and interrupts in
the ACPM TMU child node. Usually the clocks and interrupts belong to the
node that contains the reg property. But I guess that's alright because
the interrupts property is expected to be in the node that the driver
binds to. For the clocks, by placing it in the ACPM child node, I allow
runtime PM to manage it.

Do you think the below description is accurate?

soc: soc@0 {
    tmu_top: thermal-sensor@...a0000 {
        compatible = "google,gs101-tmu-top";
        reg = <0x100a0000 0x800>;
    };
};

firmware {
    acpm_ipc: power-management {
        compatible = "google,gs101-acpm-ipc";
        /* ... */

        thermal-sensor {
            compatible = "google,gs101-acpm-tmu-top";
            clocks = <&cmu_misc CLK_GOUT_MISC_TMU_TOP_PCLK>;
            interrupts = <GIC_SPI 769 IRQ_TYPE_LEVEL_HIGH 0>;
            samsung,tmu-regs = <&tmu_top>; 
            #thermal-sensor-cells = <1>;
        };
    };
};

Thanks!
ta