linux-kernel - Re: [PATCH v2 2/4] soc: qcom: rpmh: Add support to read back resource settings

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Message-ID: <ef247fe6-6d9c-4a74-b3f8-a56857332758@oss.qualcomm.com>
Date: Thu, 23 Oct 2025 11:09:07 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: "Maulik Shah (mkshah)" <maulik.shah@....qualcomm.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Kamal Wadhwa <kamal.wadhwa@....qualcomm.com>
Cc: Konrad Dybcio <konradybcio@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] soc: qcom: rpmh: Add support to read back resource
 settings

On 10/23/25 10:57 AM, Maulik Shah (mkshah) wrote:
> 
> 
> On 10/23/2025 1:47 PM, Konrad Dybcio wrote:
>> On 10/23/25 6:46 AM, Maulik Shah (mkshah) wrote:
>>>
>>>
>>> On 10/23/2025 2:51 AM, Bjorn Andersson wrote:
>>>> On Wed, Oct 22, 2025 at 02:38:54AM +0530, Kamal Wadhwa wrote:
>>>>> From: Maulik Shah <maulik.shah@....qualcomm.com>
>>>>>
>>>>> All rpmh_*() APIs so far have supported placing votes for various
>>>>> resource settings but the H/W also have option to read resource
>>>>> settings.
>>>>>
>>>>> This change adds a new rpmh_read() API to allow clients
>>>>> to read back resource setting from H/W. This will be useful for
>>>>> clients like regulators, which currently don't have a way to know
>>>>> the settings applied during bootloader stage.
>>>>>
>>>>
>>>> Allow me to express my disappointment over the fact that you sat on this
>>>> for 7 years!
>>>
>>> This was a dead API (even in downstream) with no user since SDM845/ 7 years.
>>> Read support was eventually removed from downstream driver too for the same reason.
>>> There were early discussions to remove read support from RSC H/W, due to lack of users.
>>> Its not realized yet and all SoCs still supports read.
>>
>> Can we read BCM states from HLOS this way too?
> 
> Yes, Any of ARC/BCM/VRM can be read to get HLOS/DRV2 votes.

Wow this is amazing..

Do you have code for this already, or should I hack on it?

Konrad